predict.c

/***************************************************************************\
*          PREDICT: A satellite tracking/orbital prediction program         *
*          Project started 26-May-1991 by John A. Magliacane, KD2BD         *
*                        Last update: 14-May-2006                           *
*****************************************************************************
*                                                                           *
* This program is free software; you can redistribute it and/or modify it   *
* under the terms of the GNU General Public License as published by the     *
* Free Software Foundation; either version 2 of the License or any later    *
* version.                                                                  *
*                                                                           *
* This program is distributed in the hope that it will be useful,           *
* but WITHOUT ANY WARRANTY; without even the implied warranty of            *
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU         *
* General Public License for more details.                                  *
*                                                                           *
*****************************************************************************
*          See the "CREDITS" file for the names of those who have           *
*   generously contributed their time, talent, and effort to this project.  *
\***************************************************************************/

#include <Python.h>
#include <stdio.h>
#include <math.h>
#include <time.h>
#include <sys/time.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <unistd.h>
#include <fcntl.h>
#include <termios.h>

#define VERSION "2.2.3"

/* Constants used by SGP4/SDP4 code */

#define	km2mi		0.621371		/* km to miles */
#define deg2rad		1.745329251994330E-2	/* Degrees to radians */
#define pi		3.14159265358979323846	/* Pi */
#define pio2		1.57079632679489656	/* Pi/2 */
#define x3pio2		4.71238898038468967	/* 3*Pi/2 */
#define twopi		6.28318530717958623	/* 2*Pi  */
#define e6a		1.0E-6
#define tothrd		6.6666666666666666E-1	/* 2/3 */
#define xj2		1.0826158E-3		/* J2 Harmonic (WGS '72) */
#define xj3		-2.53881E-6		/* J3 Harmonic (WGS '72) */
#define xj4		-1.65597E-6		/* J4 Harmonic (WGS '72) */
#define xke		7.43669161E-2
#define xkmper		6.378137E3		/* WGS 84 Earth radius km */
#define xmnpda		1.44E3			/* Minutes per day */
#define ae		1.0
#define ck2		5.413079E-4
#define ck4		6.209887E-7
#define f		3.35281066474748E-3	/* Flattening factor */
#define ge		3.986008E5 	/* Earth gravitational constant (WGS '72) */
#define s		1.012229
#define qoms2t		1.880279E-09
#define secday		8.6400E4	/* Seconds per day */
#define omega_E		1.00273790934	/* Earth rotations/siderial day */
#define omega_ER	6.3003879	/* Earth rotations, rads/siderial day */
#define zns		1.19459E-5
#define c1ss		2.9864797E-6
#define zes		1.675E-2
#define znl		1.5835218E-4
#define c1l		4.7968065E-7
#define zel		5.490E-2
#define zcosis		9.1744867E-1
#define zsinis		3.9785416E-1
#define zsings		-9.8088458E-1
#define zcosgs		1.945905E-1
#define zcoshs		1
#define zsinhs		0
#define q22		1.7891679E-6
#define q31		2.1460748E-6
#define q33		2.2123015E-7
#define g22		5.7686396
#define g32		9.5240898E-1
#define g44		1.8014998
#define g52		1.0508330
#define g54		4.4108898
#define root22		1.7891679E-6
#define root32		3.7393792E-7
#define root44		7.3636953E-9
#define root52		1.1428639E-7
#define root54		2.1765803E-9
#define thdt		4.3752691E-3
#define rho		1.5696615E-1
#define mfactor		7.292115E-5
#define sr		6.96000E5	/* Solar radius - km (IAU 76) */
#define AU		1.49597870691E8	/* Astronomical unit - km (IAU 76) */

/* Entry points of Deep() */

#define dpinit   1 /* Deep-space initialization code */
#define dpsec    2 /* Deep-space secular code        */
#define dpper    3 /* Deep-space periodic code       */

/* Flow control flag definitions */

#define ALL_FLAGS              -1
#define SGP_INITIALIZED_FLAG   0x000001	/* not used */
#define SGP4_INITIALIZED_FLAG  0x000002
#define SDP4_INITIALIZED_FLAG  0x000004
#define SGP8_INITIALIZED_FLAG  0x000008	/* not used */
#define SDP8_INITIALIZED_FLAG  0x000010	/* not used */
#define SIMPLE_FLAG            0x000020
#define DEEP_SPACE_EPHEM_FLAG  0x000040
#define LUNAR_TERMS_DONE_FLAG  0x000080
#define NEW_EPHEMERIS_FLAG     0x000100	/* not used */
#define DO_LOOP_FLAG           0x000200
#define RESONANCE_FLAG         0x000400
#define SYNCHRONOUS_FLAG       0x000800
#define EPOCH_RESTART_FLAG     0x001000
#define VISIBLE_FLAG           0x002000
#define SAT_ECLIPSED_FLAG      0x004000

// Python Extension Globals
static PyObject *PredictException;
static PyObject *NoTransitException;

// This struct represents an observation of a particular satellite
// from a particular reference point (on earth) at a particular time
// and is used primarily in the PyPredict code.
typedef struct observation {
	double epoch;
	char orbital_model[5];
	long norad_id;
	char name[25];
	double latitude;
	double longitude;
	double altitude;
	double orbital_velocity;
	double footprint;
	double eclipse_depth;
	double orbital_phase;
	char sunlit;
	long orbit;
	char geostationary;
	double azimuth;
	double elevation;
	double slant_range;
	char visibility;
	char has_aos;
	char decayed;
	double doppler;
	double eci_x;
	double eci_y;
	double eci_z;
	double eci_vx;
	double eci_vy;
	double eci_vz;
	double eci_sun_x;
	double eci_sun_y;
	double eci_sun_z;
	double eci_obs_x;
	double eci_obs_y;
	double eci_obs_z;
	double beta_angle;

} observation;

struct	{
	   char line1[70];       // First line of TLE
	   char line2[70];       // Second line of TLE
	   char name[25];        // Spacecraft Name
 	   long catnum;          // Catalog Number (a.k.a NORAD id)
	   long setnum;          // Element Set No.
	   char designator[10];  // Designator
	   int year;             // Reference Epoch from TLE (2-digit year)
	   double refepoch;      // Reference Epoch from TLE (day of the year and fractional portion of the day)
	   double incl;          // Inclination
	   double raan;          // RAAN
	   double eccn;          // Eccentricity
	   double argper;        // Arg of Perigee
	   double meanan;        // Mean Anomaly
	   double meanmo;        // Mean Motion
	   double drag;          // Decay Rate
	   double nddot6;        // Nddot/6
  	   double bstar;         // Bstar Drag Term
	   long orbitnum;        // Orbit Number
	}  sat;

struct	{
       char callsign[17];    // Observation Position Call Sign
	   double stnlat;        // Observation Position Latitude
	   double stnlong;       // Observation Position Longitude
	   int stnalt;           // Observation Position Altitude
	}  qth;

// TODO: sat_db doesn't seem to be used much.  Verify it functions and annotate.
struct	{  char name[25];
	   long catnum;
	   char squintflag;
	   double alat;
	   double alon;
	   unsigned char transponders;
	   char transponder_name[10][80];
	   double uplink_start[10];
	   double uplink_end[10];
	   double downlink_start[10];
	   double downlink_end[10];
	   unsigned char dayofweek[10];
	   int phase_start[10];
	   int phase_end[10];
	}  sat_db;

/* Global variables for sharing data among functions... */

double	tsince, jul_epoch, jul_utc, eclipse_depth=0,
	sat_azi, sat_ele, sat_range, sat_range_rate,
	sat_lat, sat_lon, sat_alt, sat_vel, phase,
	sun_azi, sun_ele, daynum, fm, fk, age, aostime,
	lostime, ax, ay, az, rx, ry, rz, squint, alat, alon,
	eci_x, eci_y, eci_z, eci_vx, eci_vy, eci_vz, beta_angle,
	eci_sun_x, eci_sun_y, eci_sun_z, eci_obs_x, eci_obs_y, eci_obs_z,
	sun_ra, sun_dec, sun_lat, sun_lon, sun_range, sun_range_rate,
	moon_az, moon_el, moon_dx, moon_ra, moon_dec, moon_gha, moon_dv;

char	qthfile[50], tlefile[50], dbfile[50], temp[80], output[25],
	ephem[5], sat_sun_status, findsun, calc_squint;

int	indx, iaz, iel, ma256, isplat, isplong, Flags=0;

long	rv, irk;

unsigned char val[256];

/** Type definitions **/

/* Two-line-element satellite orbital data
   structure used directly by the SGP4/SDP4 code. */

typedef struct	{
		   double  epoch, xndt2o, xndd6o, bstar, xincl,
			   xnodeo, eo, omegao, xmo, xno;
 		   int	   catnr, elset, revnum;
 		   char	   sat_name[25], idesg[9];
		}  tle_t;

/* Geodetic position structure used by SGP4/SDP4 code. */

typedef struct	{
		   double lat, lon, alt, theta;
		}  geodetic_t;

/* General three-dimensional vector structure used by SGP4/SDP4 code. */

typedef struct	{
		   double x, y, z, w;
		}  vector_t;

/* Common arguments between deep-space functions used by SGP4/SDP4 code. */

typedef struct	{
		   	   /* Used by dpinit part of Deep() */
		   double  eosq, sinio, cosio, betao, aodp, theta2,
			   sing, cosg, betao2, xmdot, omgdot, xnodot, xnodp;

			   /* Used by dpsec and dpper parts of Deep() */
		   double  xll, omgadf, xnode, em, xinc, xn, t;

		 	   /* Used by thetg and Deep() */
		   double  ds50;
		}  deep_arg_t;

/* Global structure used by SGP4/SDP4 code. */

geodetic_t obs_geodetic;

/* Two-line Orbital Elements for the satellite used by SGP4/SDP4 code. */

tle_t tle;

/* Functions for testing and setting/clearing flags used in SGP4/SDP4 code */

int isFlagSet(int flag)
{
	return (Flags&flag);
}

int isFlagClear(int flag)
{
	return (~Flags&flag);
}

void SetFlag(int flag)
{
	Flags|=flag;
}

void ClearFlag(int flag)
{
	Flags&=~flag;
}

/* Remaining SGP4/SDP4 code follows... */

int Sign(double arg)
{
	/* Returns sign of a double */

	if (arg>0)
	{
		return 1;
	}

	else if (arg<0)
	{
		return -1;
	}

	else
	{
		return 0;
	}
}

double Sqr(double arg)
{
	/* Returns square of a double */
	return (arg*arg);
}

double Cube(double arg)
{
	/* Returns cube of a double */
	return (arg*arg*arg);
}

double Radians(double arg)
{
	/* Returns angle in radians from argument in degrees */
	return (arg*deg2rad);
}

double Degrees(double arg)
{
	/* Returns angle in degrees from argument in radians */
	return (arg/deg2rad);
}

double ArcSin(double arg)
{
	/* Returns the arcsine of the argument */

	if (fabs(arg)>=1.0)
	{
		return(Sign(arg)*pio2);
	}
	else
	{
	return(atan(arg/sqrt(1.0-arg*arg)));
	}
}

double ArcCos(double arg)
{
	/* Returns arccosine of argument */
	return(pio2-ArcSin(arg));
}

void Magnitude(vector_t *v)
{
	/* Calculates scalar magnitude of a vector_t argument */
	v->w=sqrt(Sqr(v->x)+Sqr(v->y)+Sqr(v->z));
}

void Vec_Add(vector_t *v1, vector_t *v2, vector_t *v3)
{
	/* Adds vectors v1 and v2 together to produce v3 */
	v3->x=v1->x+v2->x;
	v3->y=v1->y+v2->y;
	v3->z=v1->z+v2->z;
	Magnitude(v3);
}

void Vec_Sub(vector_t *v1, vector_t *v2, vector_t *v3)
{
	/* Subtracts vector v2 from v1 to produce v3 */
	v3->x=v1->x-v2->x;
	v3->y=v1->y-v2->y;
	v3->z=v1->z-v2->z;
	Magnitude(v3);
}

void Scalar_Multiply(double k, vector_t *v1, vector_t *v2)
{
	/* Multiplies the vector v1 by the scalar k to produce the vector v2 */
	v2->x=k*v1->x;
	v2->y=k*v1->y;
	v2->z=k*v1->z;
	v2->w=fabs(k)*v1->w;
}

void Scale_Vector(double k, vector_t *v)
{
	/* Multiplies the vector v1 by the scalar k */
	v->x*=k;
	v->y*=k;
	v->z*=k;
	Magnitude(v);
}

double Dot(vector_t *v1, vector_t *v2)
{
	/* Returns the dot product of two vectors */
	return (v1->x*v2->x+v1->y*v2->y+v1->z*v2->z);
}

double Angle(vector_t *v1, vector_t *v2)
{
	/* Calculates the angle between vectors v1 and v2 */
	Magnitude(v1);
	Magnitude(v2);
	return(ArcCos(Dot(v1,v2)/(v1->w*v2->w)));
}

void Cross(vector_t *v1, vector_t *v2 ,vector_t *v3)
{
	/* Produces cross product of v1 and v2, and returns in v3 */
	v3->x=v1->y*v2->z-v1->z*v2->y;
	v3->y=v1->z*v2->x-v1->x*v2->z;
	v3->z=v1->x*v2->y-v1->y*v2->x;
	Magnitude(v3);
}

void Normalize(vector_t *v)
{
	/* Normalizes a vector */
	v->x/=v->w;
	v->y/=v->w;
	v->z/=v->w;
}

double AcTan(double sinx, double cosx)
{
	/* Four-quadrant arctan function */

	if (cosx==0.0)
	{
		if (sinx>0.0)
		{
			return (pio2);
		}
		else
		{
			return (x3pio2);
		}
	}

	else
	{
		if (cosx>0.0)
		{
			if (sinx>0.0)
			{
				return (atan(sinx/cosx));
			}
			else
			{
				return (twopi+atan(sinx/cosx));
			}
		}

		else
		{
			return (pi+atan(sinx/cosx));
		}
	}
}

double FMod2p(double x)
{
	/* Returns mod 2PI of argument */

	int i;
	double ret_val;

	ret_val=x;
	i=ret_val/twopi;
	ret_val-=i*twopi;

	if (ret_val<0.0)
	{
		ret_val+=twopi;
	}

	return ret_val;
}

double Modulus(double arg1, double arg2)
{
	/* Returns arg1 mod arg2 */

	int i;
	double ret_val;

	ret_val=arg1;
	i=ret_val/arg2;
	ret_val-=i*arg2;

	if (ret_val<0.0)
	{
		ret_val+=arg2;
	}

	return ret_val;
}

double Frac(double arg)
{
	/* Returns fractional part of double argument */
	return(arg-floor(arg));
}

int Round(double arg)
{
	/* Returns argument rounded up to nearest integer */
	return((int)floor(arg+0.5));
}

double Int(double arg)
{
	/* Returns the floor integer of a double arguement, as double */
	return(floor(arg));
}

void Convert_Sat_State(vector_t *pos, vector_t *vel)
{
	/* Converts the satellite's position and velocity  */
	/* vectors from normalized values to km and km/sec */
	Scale_Vector(xkmper, pos);
	Scale_Vector(xkmper*xmnpda/secday, vel);
}

double Julian_Date_of_Year(double year)
{
	/* The function Julian_Date_of_Year calculates the Julian Date  */
	/* of Day 0.0 of {year}. This function is used to calculate the */
	/* Julian Date of any date by using Julian_Date_of_Year, DOY,   */
	/* and Fraction_of_Day. */

	/* Astronomical Formulae for Calculators, Jean Meeus, */
	/* pages 23-25. Calculate Julian Date of 0.0 Jan year */

	long A, B, i;
	double jdoy;

	year=year-1;
	i=year/100;
	A=i;
	i=A/4;
	B=2-A+i;
	i=365.25*year;
	i+=30.6001*14;
	jdoy=i+1720994.5+B;

	return jdoy;
}

double Julian_Date_of_Epoch(double epoch)
{
	/* The function Julian_Date_of_Epoch returns the Julian Date of     */
	/* an epoch specified in the format used in the NORAD two-line      */
	/* element sets. It has been modified to support dates beyond       */
	/* the year 1999 assuming that two-digit years in the range 00-56   */
	/* correspond to 2000-2056. Until the two-line element set format   */
	/* is changed, it is only valid for dates through 2056 December 31. */

	double year, day;

	/* Modification to support Y2K */
	/* Valid 1957 through 2056     */

	day=modf(epoch*1E-3, &year)*1E3;

	if (year<57)
	{
		year=year+2000;
	}
	else
	{
		year=year+1900;
	}

	return (Julian_Date_of_Year(year)+day);
}

int DOY (int yr, int mo, int dy)
{
	/* The function DOY calculates the day of the year for the specified */
	/* date. The calculation uses the rules for the Gregorian calendar   */
	/* and is valid from the inception of that calendar system.          */

	const int days[] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
	int i, day;

	day=0;

	for (i=0; i<mo-1; i++ )
	{
	    day+=days[i];
	}

	day=day+dy;

	/* Leap year correction */

	if ((yr%4==0) && ((yr%100!=0) || (yr%400==0)) && (mo>2))
	{
		day++;
	}

	return day;
}

double Fraction_of_Day(int hr, int mi, double se)
{
	/* Fraction_of_Day calculates the fraction of */
	/* a day passed at the specified input time.  */

	double dhr, dmi;

	dhr=(double)hr;
	dmi=(double)mi;

	return ((dhr+(dmi+se/60.0)/60.0)/24.0);
}

double Julian_Date(struct tm *cdate)
{
	/* The function Julian_Date converts a standard calendar   */
	/* date and time to a Julian Date. The procedure Date_Time */
	/* performs the inverse of this function. */

	double julian_date;

	julian_date=Julian_Date_of_Year(cdate->tm_year)+DOY(cdate->tm_year,cdate->tm_mon,cdate->tm_mday)+Fraction_of_Day(cdate->tm_hour,cdate->tm_min,cdate->tm_sec)+5.787037e-06; /* Round up to nearest 1 sec */

	return julian_date;
}

void Date_Time(double julian_date, struct tm *cdate)
{
	/* The function Date_Time() converts a Julian Date to
	standard calendar date and time. The function
	Julian_Date() performs the inverse of this function. */

	time_t jtime;

	jtime=(julian_date-2440587.5)*86400.0;
	*cdate=*gmtime(&jtime);
}

double Delta_ET(double year)
{
	/* The function Delta_ET has been added to allow calculations on   */
	/* the position of the sun.  It provides the difference between UT */
	/* (approximately the same as UTC) and ET (now referred to as TDT).*/
	/* This function is based on a least squares fit of data from 1950 */
	/* to 1991 and will need to be updated periodically. */

	/* Values determined using data from 1950-1991 in the 1990
	Astronomical Almanac.  See DELTA_ET.WQ1 for details. */

	double delta_et;

	delta_et=26.465+0.747622*(year-1950)+1.886913*sin(twopi*(year-1975)/33);

	return delta_et;
}

double ThetaG(double epoch, deep_arg_t *deep_arg)
{
	/* The function ThetaG calculates the Greenwich Mean Sidereal Time */
	/* for an epoch specified in the format used in the NORAD two-line */
	/* element sets. It has now been adapted for dates beyond the year */
	/* 1999, as described above. The function ThetaG_JD provides the   */
	/* same calculation except that it is based on an input in the     */
	/* form of a Julian Date. */

	/* Reference:  The 1992 Astronomical Almanac, page B6. */

	double year, day, UT, jd, TU, GMST, ThetaG;

	/* Modification to support Y2K */
	/* Valid 1957 through 2056     */

	day=modf(epoch*1E-3,&year)*1E3;

	if (year<57)
	{
		year+=2000;
	}
	else
	{
		year+=1900;
	}

	UT=modf(day,&day);
	jd=Julian_Date_of_Year(year)+day;
	TU=(jd-2451545.0)/36525;
	GMST=24110.54841+TU*(8640184.812866+TU*(0.093104-TU*6.2E-6));
	GMST=Modulus(GMST+secday*omega_E*UT,secday);
	ThetaG=twopi*GMST/secday;
	deep_arg->ds50=jd-2433281.5+UT;
	ThetaG=FMod2p(6.3003880987*deep_arg->ds50+1.72944494);

	return ThetaG;
}

double ThetaG_JD(double jd)
{
	/* Reference:  The 1992 Astronomical Almanac, page B6. */

	double UT, TU, GMST;

	UT=Frac(jd+0.5);
	jd=jd-UT;
	TU=(jd-2451545.0)/36525;
	GMST=24110.54841+TU*(8640184.812866+TU*(0.093104-TU*6.2E-6));
	GMST=Modulus(GMST+secday*omega_E*UT,secday);

	return (twopi*GMST/secday);
}

void Calculate_Solar_Position(double time, vector_t *solar_vector)
{
	/* Calculates solar position vector */

	double mjd, year, T, M, L, e, C, O, Lsa, nu, R, eps;

	mjd=time-2415020.0;
	year=1900+mjd/365.25;
	T=(mjd+Delta_ET(year)/secday)/36525.0;
	M=Radians(Modulus(358.47583+Modulus(35999.04975*T,360.0)-(0.000150+0.0000033*T)*Sqr(T),360.0));
	L=Radians(Modulus(279.69668+Modulus(36000.76892*T,360.0)+0.0003025*Sqr(T),360.0));
	e=0.01675104-(0.0000418+0.000000126*T)*T;
	C=Radians((1.919460-(0.004789+0.000014*T)*T)*sin(M)+(0.020094-0.000100*T)*sin(2*M)+0.000293*sin(3*M));
	O=Radians(Modulus(259.18-1934.142*T,360.0));
	Lsa=Modulus(L+C-Radians(0.00569-0.00479*sin(O)),twopi);
	nu=Modulus(M+C,twopi);
	R=1.0000002*(1.0-Sqr(e))/(1.0+e*cos(nu));
	eps=Radians(23.452294-(0.0130125+(0.00000164-0.000000503*T)*T)*T+0.00256*cos(O));
	R=AU*R;
	solar_vector->x=R*cos(Lsa);
	solar_vector->y=R*sin(Lsa)*cos(eps);
	solar_vector->z=R*sin(Lsa)*sin(eps);
	solar_vector->w=R;
}

int Sat_Eclipsed(vector_t *pos, vector_t *sol, double *depth)
{
	/* Calculates satellite's eclipse status and depth */

	double sd_sun, sd_earth, delta;
	vector_t Rho, earth;

	/* Determine partial eclipse */

	sd_earth=ArcSin(xkmper/pos->w);
	Vec_Sub(sol,pos,&Rho);
	sd_sun=ArcSin(sr/Rho.w);
	Scalar_Multiply(-1,pos,&earth);
	delta=Angle(sol,&earth);
	*depth=sd_earth-sd_sun-delta;

	if (sd_earth<sd_sun)
	{
		return 0;
	}
	else if (*depth>=0)
	{
		return 1;
	}
	else
	{
		return 0;
	}
}

void select_ephemeris(tle_t *tle)
{
	/* Selects the apropriate ephemeris type to be used */
	/* for predictions according to the data in the TLE */
	/* It also processes values in the tle set so that  */
	/* they are apropriate for the sgp4/sdp4 routines   */

	double ao, xnodp, dd1, dd2, delo, temp, a1, del1, r1;

	/* Preprocess tle set */
	tle->xnodeo*=deg2rad;
	tle->omegao*=deg2rad;
	tle->xmo*=deg2rad;
	tle->xincl*=deg2rad;
	temp=twopi/xmnpda/xmnpda;
	tle->xno=tle->xno*temp*xmnpda;
	tle->xndt2o*=temp;
	tle->xndd6o=tle->xndd6o*temp/xmnpda;
	tle->bstar/=ae;

	/* Period > 225 minutes is deep space */
	dd1=(xke/tle->xno);
	dd2=tothrd;
	a1=pow(dd1,dd2);
	r1=cos(tle->xincl);
	dd1=(1.0-tle->eo*tle->eo);
	temp=ck2*1.5f*(r1*r1*3.0-1.0)/pow(dd1,1.5);
	del1=temp/(a1*a1);
	ao=a1*(1.0-del1*(tothrd*.5+del1*(del1*1.654320987654321+1.0)));
	delo=temp/(ao*ao);
	xnodp=tle->xno/(delo+1.0);

	/* Select a deep-space/near-earth ephemeris */

	if (twopi/xnodp/xmnpda>=0.15625)
	{
		SetFlag(DEEP_SPACE_EPHEM_FLAG);
	}
	else
	{
		ClearFlag(DEEP_SPACE_EPHEM_FLAG);
	}
}

void SGP4(double tsince, tle_t * tle, vector_t * pos, vector_t * vel)
{
	/* This function is used to calculate the position and velocity */
	/* of near-earth (period < 225 minutes) satellites. tsince is   */
	/* time since epoch in minutes, tle is a pointer to a tle_t     */
	/* structure with Keplerian orbital elements and pos and vel    */
	/* are vector_t structures returning ECI satellite position and */
	/* velocity. Use Convert_Sat_State() to convert to km and km/s. */

	static double aodp, aycof, c1, c4, c5, cosio, d2, d3, d4, delmo,
	omgcof, eta, omgdot, sinio, xnodp, sinmo, t2cof, t3cof, t4cof,
	t5cof, x1mth2, x3thm1, x7thm1, xmcof, xmdot, xnodcf, xnodot, xlcof;

	double cosuk, sinuk, rfdotk, vx, vy, vz, ux, uy, uz, xmy, xmx, cosnok,
	sinnok, cosik, sinik, rdotk, xinck, xnodek, uk, rk, cos2u, sin2u,
	u, sinu, cosu, betal, rfdot, rdot, r, pl, elsq, esine, ecose, epw,
	cosepw, x1m5th, xhdot1, tfour, sinepw, capu, ayn, xlt, aynl, xll,
	axn, xn, beta, xl, e, a, tcube, delm, delomg, templ, tempe, tempa,
	xnode, tsq, xmp, omega, xnoddf, omgadf, xmdf, a1, a3ovk2, ao,
	betao, betao2, c1sq, c2, c3, coef, coef1, del1, delo, eeta, eosq,
	etasq, perigee, pinvsq, psisq, qoms24, s4, temp, temp1, temp2,
	temp3, temp4, temp5, temp6, theta2, theta4, tsi;

	int i;

	/* Initialization */

	if (isFlagClear(SGP4_INITIALIZED_FLAG))
	{
		SetFlag(SGP4_INITIALIZED_FLAG);

		/* Recover original mean motion (xnodp) and   */
		/* semimajor axis (aodp) from input elements. */

		a1=pow(xke/tle->xno,tothrd);
		cosio=cos(tle->xincl);
		theta2=cosio*cosio;
		x3thm1=3*theta2-1.0;
		eosq=tle->eo*tle->eo;
		betao2=1.0-eosq;
		betao=sqrt(betao2);
		del1=1.5*ck2*x3thm1/(a1*a1*betao*betao2);
		ao=a1*(1.0-del1*(0.5*tothrd+del1*(1.0+134.0/81.0*del1)));
		delo=1.5*ck2*x3thm1/(ao*ao*betao*betao2);
		xnodp=tle->xno/(1.0+delo);
		aodp=ao/(1.0-delo);

		/* For perigee less than 220 kilometers, the "simple"     */
		/* flag is set and the equations are truncated to linear  */
		/* variation in sqrt a and quadratic variation in mean    */
		/* anomaly.  Also, the c3 term, the delta omega term, and */
		/* the delta m term are dropped.                          */

		if ((aodp*(1-tle->eo)/ae)<(220/xkmper+ae))
		{
		    SetFlag(SIMPLE_FLAG);
		}

		else
		{
		    ClearFlag(SIMPLE_FLAG);
		}

		/* For perigees below 156 km, the      */
		/* values of s and qoms2t are altered. */

		s4=s;
		qoms24=qoms2t;
		perigee=(aodp*(1-tle->eo)-ae)*xkmper;

		if (perigee<156.0)
		{
			if (perigee<=98.0)
			{
			    s4=20;
			}
			else
			{
		   	 s4=perigee-78.0;
			}

			qoms24=pow((120-s4)*ae/xkmper,4);
			s4=s4/xkmper+ae;
		}

		pinvsq=1/(aodp*aodp*betao2*betao2);
		tsi=1/(aodp-s4);
		eta=aodp*tle->eo*tsi;
		etasq=eta*eta;
		eeta=tle->eo*eta;
		psisq=fabs(1-etasq);
		coef=qoms24*pow(tsi,4);
		coef1=coef/pow(psisq,3.5);
		c2=coef1*xnodp*(aodp*(1+1.5*etasq+eeta*(4+etasq))+0.75*ck2*tsi/psisq*x3thm1*(8+3*etasq*(8+etasq)));
		c1=tle->bstar*c2;
		sinio=sin(tle->xincl);
		a3ovk2=-xj3/ck2*pow(ae,3);
		c3=coef*tsi*a3ovk2*xnodp*ae*sinio/tle->eo;
		x1mth2=1-theta2;

		c4=2*xnodp*coef1*aodp*betao2*(eta*(2+0.5*etasq)+tle->eo*(0.5+2*etasq)-2*ck2*tsi/(aodp*psisq)*(-3*x3thm1*(1-2*eeta+etasq*(1.5-0.5*eeta))+0.75*x1mth2*(2*etasq-eeta*(1+etasq))*cos(2*tle->omegao)));
		c5=2*coef1*aodp*betao2*(1+2.75*(etasq+eeta)+eeta*etasq);

		theta4=theta2*theta2;
		temp1=3*ck2*pinvsq*xnodp;
		temp2=temp1*ck2*pinvsq;
		temp3=1.25*ck4*pinvsq*pinvsq*xnodp;
		xmdot=xnodp+0.5*temp1*betao*x3thm1+0.0625*temp2*betao*(13-78*theta2+137*theta4);
		x1m5th=1-5*theta2;
		omgdot=-0.5*temp1*x1m5th+0.0625*temp2*(7-114*theta2+395*theta4)+temp3*(3-36*theta2+49*theta4);
		xhdot1=-temp1*cosio;
		xnodot=xhdot1+(0.5*temp2*(4-19*theta2)+2*temp3*(3-7*theta2))*cosio;
		omgcof=tle->bstar*c3*cos(tle->omegao);
		xmcof=-tothrd*coef*tle->bstar*ae/eeta;
		xnodcf=3.5*betao2*xhdot1*c1;
		t2cof=1.5*c1;
		xlcof=0.125*a3ovk2*sinio*(3+5*cosio)/(1+cosio);
		aycof=0.25*a3ovk2*sinio;
		delmo=pow(1+eta*cos(tle->xmo),3);
		sinmo=sin(tle->xmo);
		x7thm1=7*theta2-1;

		if (isFlagClear(SIMPLE_FLAG))
		{
			c1sq=c1*c1;
			d2=4*aodp*tsi*c1sq;
			temp=d2*tsi*c1/3;
			d3=(17*aodp+s4)*temp;
			d4=0.5*temp*aodp*tsi*(221*aodp+31*s4)*c1;
			t3cof=d2+2*c1sq;
			t4cof=0.25*(3*d3+c1*(12*d2+10*c1sq));
			t5cof=0.2*(3*d4+12*c1*d3+6*d2*d2+15*c1sq*(2*d2+c1sq));
		}
	}

	/* Update for secular gravity and atmospheric drag. */
	xmdf=tle->xmo+xmdot*tsince;
	omgadf=tle->omegao+omgdot*tsince;
	xnoddf=tle->xnodeo+xnodot*tsince;
	omega=omgadf;
	xmp=xmdf;
	tsq=tsince*tsince;
	xnode=xnoddf+xnodcf*tsq;
	tempa=1-c1*tsince;
	tempe=tle->bstar*c4*tsince;
	templ=t2cof*tsq;

	if (isFlagClear(SIMPLE_FLAG))
	{
		delomg=omgcof*tsince;
		delm=xmcof*(pow(1+eta*cos(xmdf),3)-delmo);
		temp=delomg+delm;
		xmp=xmdf+temp;
		omega=omgadf-temp;
		tcube=tsq*tsince;
		tfour=tsince*tcube;
		tempa=tempa-d2*tsq-d3*tcube-d4*tfour;
		tempe=tempe+tle->bstar*c5*(sin(xmp)-sinmo);
		templ=templ+t3cof*tcube+tfour*(t4cof+tsince*t5cof);
	}

	a=aodp*pow(tempa,2);
	e=tle->eo-tempe;
	xl=xmp+omega+xnode+xnodp*templ;
	beta=sqrt(1-e*e);
	xn=xke/pow(a,1.5);

	/* Long period periodics */
	axn=e*cos(omega);
	temp=1/(a*beta*beta);
	xll=temp*xlcof*axn;
	aynl=temp*aycof;
	xlt=xl+xll;
	ayn=e*sin(omega)+aynl;

	/* Solve Kepler's Equation */
	capu=FMod2p(xlt-xnode);
	temp2=capu;
	i=0;

	do
	{
		sinepw=sin(temp2);
		cosepw=cos(temp2);
		temp3=axn*sinepw;
		temp4=ayn*cosepw;
		temp5=axn*cosepw;
		temp6=ayn*sinepw;
		epw=(capu-temp4+temp3-temp2)/(1-temp5-temp6)+temp2;

		if (fabs(epw-temp2)<= e6a)
		{
			break;
		}

		temp2=epw;

	} while (i++<10);

	/* Short period preliminary quantities */
	ecose=temp5+temp6;
	esine=temp3-temp4;
	elsq=axn*axn+ayn*ayn;
	temp=1-elsq;
	pl=a*temp;
	r=a*(1-ecose);
	temp1=1/r;
	rdot=xke*sqrt(a)*esine*temp1;
	rfdot=xke*sqrt(pl)*temp1;
	temp2=a*temp1;
	betal=sqrt(temp);
	temp3=1/(1+betal);
	cosu=temp2*(cosepw-axn+ayn*esine*temp3);
	sinu=temp2*(sinepw-ayn-axn*esine*temp3);
	u=AcTan(sinu,cosu);
	sin2u=2*sinu*cosu;
	cos2u=2*cosu*cosu-1;
	temp=1/pl;
	temp1=ck2*temp;
	temp2=temp1*temp;

	/* Update for short periodics */
	rk=r*(1-1.5*temp2*betal*x3thm1)+0.5*temp1*x1mth2*cos2u;
	uk=u-0.25*temp2*x7thm1*sin2u;
	xnodek=xnode+1.5*temp2*cosio*sin2u;
	xinck=tle->xincl+1.5*temp2*cosio*sinio*cos2u;
	rdotk=rdot-xn*temp1*x1mth2*sin2u;
	rfdotk=rfdot+xn*temp1*(x1mth2*cos2u+1.5*x3thm1);

	/* Orientation vectors */
	sinuk=sin(uk);
	cosuk=cos(uk);
	sinik=sin(xinck);
	cosik=cos(xinck);
	sinnok=sin(xnodek);
	cosnok=cos(xnodek);
	xmx=-sinnok*cosik;
	xmy=cosnok*cosik;
	ux=xmx*sinuk+cosnok*cosuk;
	uy=xmy*sinuk+sinnok*cosuk;
	uz=sinik*sinuk;
	vx=xmx*cosuk-cosnok*sinuk;
	vy=xmy*cosuk-sinnok*sinuk;
	vz=sinik*cosuk;

	/* Position and velocity */
	pos->x=rk*ux;
	pos->y=rk*uy;
	pos->z=rk*uz;
	vel->x=rdotk*ux+rfdotk*vx;
	vel->y=rdotk*uy+rfdotk*vy;
	vel->z=rdotk*uz+rfdotk*vz;

	/* Phase in radians */
	phase=xlt-xnode-omgadf+twopi;

	if (phase<0.0)
	{
		phase+=twopi;
	}

	phase=FMod2p(phase);
}

void Deep(int ientry, tle_t * tle, deep_arg_t * deep_arg)
{
	/* This function is used by SDP4 to add lunar and solar */
	/* perturbation effects to deep-space orbit objects.    */

	static double thgr, xnq, xqncl, omegaq, zmol, zmos, savtsn, ee2, e3,
	xi2, xl2, xl3, xl4, xgh2, xgh3, xgh4, xh2, xh3, sse, ssi, ssg, xi3,
	se2, si2, sl2, sgh2, sh2, se3, si3, sl3, sgh3, sh3, sl4, sgh4, ssl,
	ssh, d3210, d3222, d4410, d4422, d5220, d5232, d5421, d5433, del1,
	del2, del3, fasx2, fasx4, fasx6, xlamo, xfact, xni, atime, stepp,
	stepn, step2, preep, pl, sghs, xli, d2201, d2211, sghl, sh1, pinc,
	pe, shs, zsingl, zcosgl, zsinhl, zcoshl, zsinil, zcosil;

	double a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, ainv2, alfdp, aqnv,
	sgh, sini2, sinis, sinok, sh, si, sil, day, betdp, dalf, bfact, c,
	cc, cosis, cosok, cosq, ctem, f322, zx, zy, dbet, dls, eoc, eq, f2,
	f220, f221, f3, f311, f321, xnoh, f330, f441, f442, f522, f523,
	f542, f543, g200, g201, g211, pgh, ph, s1, s2, s3, s4, s5, s6, s7,
	se, sel, ses, xls, g300, g310, g322, g410, g422, g520, g521, g532,
	g533, gam, sinq, sinzf, sis, sl, sll, sls, stem, temp, temp1, x1,
	x2, x2li, x2omi, x3, x4, x5, x6, x7, x8, xl, xldot, xmao, xnddt,
	xndot, xno2, xnodce, xnoi, xomi, xpidot, z1, z11, z12, z13, z2,
	z21, z22, z23, z3, z31, z32, z33, ze, zf, zm, zmo, zn, zsing,
	zsinh, zsini, zcosg, zcosh, zcosi, delt=0, ft=0;

	switch (ientry)
	{
		case dpinit:  /* Entrance for deep space initialization */
		thgr=ThetaG(tle->epoch,deep_arg);
		eq=tle->eo;
		xnq=deep_arg->xnodp;
		aqnv=1/deep_arg->aodp;
		xqncl=tle->xincl;
		xmao=tle->xmo;
		xpidot=deep_arg->omgdot+deep_arg->xnodot;
		sinq=sin(tle->xnodeo);
		cosq=cos(tle->xnodeo);
		omegaq=tle->omegao;

		/* Initialize lunar solar terms */
		day=deep_arg->ds50+18261.5;  /* Days since 1900 Jan 0.5 */

		if (day!=preep)
		{
			preep=day;
			xnodce=4.5236020-9.2422029E-4*day;
			stem=sin(xnodce);
			ctem=cos(xnodce);
			zcosil=0.91375164-0.03568096*ctem;
			zsinil=sqrt(1-zcosil*zcosil);
			zsinhl=0.089683511*stem/zsinil;
			zcoshl=sqrt(1-zsinhl*zsinhl);
			c=4.7199672+0.22997150*day;
			gam=5.8351514+0.0019443680*day;
			zmol=FMod2p(c-gam);
			zx=0.39785416*stem/zsinil;
			zy=zcoshl*ctem+0.91744867*zsinhl*stem;
			zx=AcTan(zx,zy);
			zx=gam+zx-xnodce;
			zcosgl=cos(zx);
			zsingl=sin(zx);
			zmos=6.2565837+0.017201977*day;
			zmos=FMod2p(zmos);
		    }

		  /* Do solar terms */
		  savtsn=1E20;
		  zcosg=zcosgs;
		  zsing=zsings;
		  zcosi=zcosis;
		  zsini=zsinis;
		  zcosh=cosq;
		  zsinh= sinq;
		  cc=c1ss;
		  zn=zns;
		  ze=zes;
		  zmo=zmos;
		  xnoi=1/xnq;

		  /* Loop breaks when Solar terms are done a second */
		  /* time, after Lunar terms are initialized        */

		for (;;)
		{
			/* Solar terms done again after Lunar terms are done */
			a1=zcosg*zcosh+zsing*zcosi*zsinh;
			a3=-zsing*zcosh+zcosg*zcosi*zsinh;
			a7=-zcosg*zsinh+zsing*zcosi*zcosh;
			a8=zsing*zsini;
			a9=zsing*zsinh+zcosg*zcosi*zcosh;
			a10=zcosg*zsini;
			a2=deep_arg->cosio*a7+deep_arg->sinio*a8;
			a4=deep_arg->cosio*a9+deep_arg->sinio*a10;
			a5=-deep_arg->sinio*a7+deep_arg->cosio*a8;
			a6=-deep_arg->sinio*a9+deep_arg->cosio*a10;
			x1=a1*deep_arg->cosg+a2*deep_arg->sing;
			x2=a3*deep_arg->cosg+a4*deep_arg->sing;
			x3=-a1*deep_arg->sing+a2*deep_arg->cosg;
			x4=-a3*deep_arg->sing+a4*deep_arg->cosg;
			x5=a5*deep_arg->sing;
			x6=a6*deep_arg->sing;
			x7=a5*deep_arg->cosg;
			x8=a6*deep_arg->cosg;
			z31=12*x1*x1-3*x3*x3;
			z32=24*x1*x2-6*x3*x4;
			z33=12*x2*x2-3*x4*x4;
			z1=3*(a1*a1+a2*a2)+z31*deep_arg->eosq;
			z2=6*(a1*a3+a2*a4)+z32*deep_arg->eosq;
			z3=3*(a3*a3+a4*a4)+z33*deep_arg->eosq;
			z11=-6*a1*a5+deep_arg->eosq*(-24*x1*x7-6*x3*x5);
			z12=-6*(a1*a6+a3*a5)+deep_arg->eosq*(-24*(x2*x7+x1*x8)-6*(x3*x6+x4*x5));
			z13=-6*a3*a6+deep_arg->eosq*(-24*x2*x8-6*x4*x6);
			z21=6*a2*a5+deep_arg->eosq*(24*x1*x5-6*x3*x7);
			z22=6*(a4*a5+a2*a6)+deep_arg->eosq*(24*(x2*x5+x1*x6)-6*(x4*x7+x3*x8));
			z23=6*a4*a6+deep_arg->eosq*(24*x2*x6-6*x4*x8);
			z1=z1+z1+deep_arg->betao2*z31;
			z2=z2+z2+deep_arg->betao2*z32;
			z3=z3+z3+deep_arg->betao2*z33;
			s3=cc*xnoi;
			s2=-0.5*s3/deep_arg->betao;
			s4=s3*deep_arg->betao;
			s1=-15*eq*s4;
			s5=x1*x3+x2*x4;
			s6=x2*x3+x1*x4;
			s7=x2*x4-x1*x3;
			se=s1*zn*s5;
			si=s2*zn*(z11+z13);
			sl=-zn*s3*(z1+z3-14-6*deep_arg->eosq);
			sgh=s4*zn*(z31+z33-6);
			sh=-zn*s2*(z21+z23);

			if (xqncl<5.2359877E-2)
			{
				sh=0;
			}

			ee2=2*s1*s6;
			e3=2*s1*s7;
			xi2=2*s2*z12;
			xi3=2*s2*(z13-z11);
			xl2=-2*s3*z2;
			xl3=-2*s3*(z3-z1);
			xl4=-2*s3*(-21-9*deep_arg->eosq)*ze;
			xgh2=2*s4*z32;
			xgh3=2*s4*(z33-z31);
			xgh4=-18*s4*ze;
			xh2=-2*s2*z22;
			xh3=-2*s2*(z23-z21);

			if (isFlagSet(LUNAR_TERMS_DONE_FLAG))
			{
				break;
			}

			/* Do lunar terms */
			sse=se;
			ssi=si;
			ssl=sl;
			ssh=sh/deep_arg->sinio;
			ssg=sgh-deep_arg->cosio*ssh;
			se2=ee2;
			si2=xi2;
			sl2=xl2;
			sgh2=xgh2;
			sh2=xh2;
			se3=e3;
			si3=xi3;
			sl3=xl3;
			sgh3=xgh3;
			sh3=xh3;
			sl4=xl4;
			sgh4=xgh4;
			zcosg=zcosgl;
			zsing=zsingl;
			zcosi=zcosil;
			zsini=zsinil;
			zcosh=zcoshl*cosq+zsinhl*sinq;
			zsinh=sinq*zcoshl-cosq*zsinhl;
			zn=znl;
			cc=c1l;
			ze=zel;
			zmo=zmol;
			SetFlag(LUNAR_TERMS_DONE_FLAG);
		}

		sse=sse+se;
		ssi=ssi+si;
		ssl=ssl+sl;
		ssg=ssg+sgh-deep_arg->cosio/deep_arg->sinio*sh;
		ssh=ssh+sh/deep_arg->sinio;

		/* Geopotential resonance initialization for 12 hour orbits */
		ClearFlag(RESONANCE_FLAG);
		ClearFlag(SYNCHRONOUS_FLAG);

		if (!((xnq<0.0052359877) && (xnq>0.0034906585)))
		{
			if ((xnq<0.00826) || (xnq>0.00924))
			{
			    return;
			}

			if (eq<0.5)
			{
			    return;
			}

			SetFlag(RESONANCE_FLAG);
			eoc=eq*deep_arg->eosq;
			g201=-0.306-(eq-0.64)*0.440;

			if (eq<=0.65)
			{
				g211=3.616-13.247*eq+16.290*deep_arg->eosq;
				g310=-19.302+117.390*eq-228.419*deep_arg->eosq+156.591*eoc;
				g322=-18.9068+109.7927*eq-214.6334*deep_arg->eosq+146.5816*eoc;
				g410=-41.122+242.694*eq-471.094*deep_arg->eosq+313.953*eoc;
				g422=-146.407+841.880*eq-1629.014*deep_arg->eosq+1083.435 * eoc;
				g520=-532.114+3017.977*eq-5740*deep_arg->eosq+3708.276*eoc;
			}

			else
			{
				g211=-72.099+331.819*eq-508.738*deep_arg->eosq+266.724*eoc;
				g310=-346.844+1582.851*eq-2415.925*deep_arg->eosq+1246.113*eoc;
				g322=-342.585+1554.908*eq-2366.899*deep_arg->eosq+1215.972*eoc;
				g410=-1052.797+4758.686*eq-7193.992*deep_arg->eosq+3651.957*eoc;
				g422=-3581.69+16178.11*eq-24462.77*deep_arg->eosq+12422.52*eoc;

				if (eq<=0.715)
				{
					g520=1464.74-4664.75*eq+3763.64*deep_arg->eosq;
				}

				else
				{
					g520=-5149.66+29936.92*eq-54087.36*deep_arg->eosq+31324.56*eoc;
				}
			}

			if (eq<0.7)
			{
				g533=-919.2277+4988.61*eq-9064.77*deep_arg->eosq+5542.21*eoc;
				g521=-822.71072+4568.6173*eq-8491.4146*deep_arg->eosq+5337.524*eoc;
				g532=-853.666+4690.25*eq-8624.77*deep_arg->eosq+5341.4*eoc;
			}

			else
			{
				g533=-37995.78+161616.52*eq-229838.2*deep_arg->eosq+109377.94*eoc;
				g521 =-51752.104+218913.95*eq-309468.16*deep_arg->eosq+146349.42*eoc;
				g532 =-40023.88+170470.89*eq-242699.48*deep_arg->eosq+115605.82*eoc;
			}

			sini2=deep_arg->sinio*deep_arg->sinio;
			f220=0.75*(1+2*deep_arg->cosio+deep_arg->theta2);
			f221=1.5*sini2;
			f321=1.875*deep_arg->sinio*(1-2*deep_arg->cosio-3*deep_arg->theta2);
			f322=-1.875*deep_arg->sinio*(1+2*deep_arg->cosio-3*deep_arg->theta2);
			f441=35*sini2*f220;
			f442=39.3750*sini2*sini2;
			f522=9.84375*deep_arg->sinio*(sini2*(1-2*deep_arg->cosio-5*deep_arg->theta2)+0.33333333*(-2+4*deep_arg->cosio+6*deep_arg->theta2));
			f523=deep_arg->sinio*(4.92187512*sini2*(-2-4*deep_arg->cosio+10*deep_arg->theta2)+6.56250012*(1+2*deep_arg->cosio-3*deep_arg->theta2));
			f542=29.53125*deep_arg->sinio*(2-8*deep_arg->cosio+deep_arg->theta2*(-12+8*deep_arg->cosio+10*deep_arg->theta2));
			f543=29.53125*deep_arg->sinio*(-2-8*deep_arg->cosio+deep_arg->theta2*(12+8*deep_arg->cosio-10*deep_arg->theta2));
			xno2=xnq*xnq;
			ainv2=aqnv*aqnv;
			temp1=3*xno2*ainv2;
			temp=temp1*root22;
			d2201=temp*f220*g201;
			d2211=temp*f221*g211;
			temp1=temp1*aqnv;
			temp=temp1*root32;
			d3210=temp*f321*g310;
			d3222=temp*f322*g322;
			temp1=temp1*aqnv;
			temp=2*temp1*root44;
			d4410=temp*f441*g410;
			d4422=temp*f442*g422;
			temp1=temp1*aqnv;
			temp=temp1*root52;
			d5220=temp*f522*g520;
			d5232=temp*f523*g532;
			temp=2*temp1*root54;
			d5421=temp*f542*g521;
			d5433=temp*f543*g533;
			xlamo=xmao+tle->xnodeo+tle->xnodeo-thgr-thgr;
			bfact=deep_arg->xmdot+deep_arg->xnodot+deep_arg->xnodot-thdt-thdt;
			bfact=bfact+ssl+ssh+ssh;
		}

		else
		{
			SetFlag(RESONANCE_FLAG);
			SetFlag(SYNCHRONOUS_FLAG);

			/* Synchronous resonance terms initialization */
			g200=1+deep_arg->eosq*(-2.5+0.8125*deep_arg->eosq);
			g310=1+2*deep_arg->eosq;
			g300=1+deep_arg->eosq*(-6+6.60937*deep_arg->eosq);
			f220=0.75*(1+deep_arg->cosio)*(1+deep_arg->cosio);
			f311=0.9375*deep_arg->sinio*deep_arg->sinio*(1+3*deep_arg->cosio)-0.75*(1+deep_arg->cosio);
			f330=1+deep_arg->cosio;
			f330=1.875*f330*f330*f330;
			del1=3*xnq*xnq*aqnv*aqnv;
			del2=2*del1*f220*g200*q22;
			del3=3*del1*f330*g300*q33*aqnv;
			del1=del1*f311*g310*q31*aqnv;
			fasx2=0.13130908;
			fasx4=2.8843198;
			fasx6=0.37448087;
			xlamo=xmao+tle->xnodeo+tle->omegao-thgr;
			bfact=deep_arg->xmdot+xpidot-thdt;
			bfact=bfact+ssl+ssg+ssh;
		}

		xfact=bfact-xnq;

		/* Initialize integrator */
		xli=xlamo;
		xni=xnq;
		atime=0;
		stepp=720;
		stepn=-720;
		step2=259200;

		return;

		case dpsec:  /* Entrance for deep space secular effects */
		deep_arg->xll=deep_arg->xll+ssl*deep_arg->t;
		deep_arg->omgadf=deep_arg->omgadf+ssg*deep_arg->t;
		deep_arg->xnode=deep_arg->xnode+ssh*deep_arg->t;
		deep_arg->em=tle->eo+sse*deep_arg->t;
		deep_arg->xinc=tle->xincl+ssi*deep_arg->t;

		if (deep_arg->xinc<0)
		{
			deep_arg->xinc=-deep_arg->xinc;
			deep_arg->xnode=deep_arg->xnode+pi;
			deep_arg->omgadf=deep_arg->omgadf-pi;
		}

		if (isFlagClear(RESONANCE_FLAG))
		{
		      return;
		}

		do
		{
			if ((atime==0) || ((deep_arg->t>=0) && (atime<0)) || ((deep_arg->t<0) && (atime>=0)))
			{
				/* Epoch restart */

				if (deep_arg->t>=0)
				{
					delt=stepp;
				}
				else
				{
					delt=stepn;
				}

				atime=0;
				xni=xnq;
				xli=xlamo;
			}

			else
			{
				if (fabs(deep_arg->t)>=fabs(atime))
				{
					if (deep_arg->t>0)
					{
						delt=stepp;
					}
					else
					{
						delt=stepn;
					}
				}
			}

			do
			{
				if (fabs(deep_arg->t-atime)>=stepp)
				{
					SetFlag(DO_LOOP_FLAG);
					ClearFlag(EPOCH_RESTART_FLAG);
				}

				else
				{
					ft=deep_arg->t-atime;
					ClearFlag(DO_LOOP_FLAG);
				}

				if (fabs(deep_arg->t)<fabs(atime))
				{
					if (deep_arg->t>=0)
					{
						delt=stepn;
					}
					else
					{
						delt=stepp;
					}

					SetFlag(DO_LOOP_FLAG | EPOCH_RESTART_FLAG);
				}

				/* Dot terms calculated */
				if (isFlagSet(SYNCHRONOUS_FLAG))
				{
					xndot=del1*sin(xli-fasx2)+del2*sin(2*(xli-fasx4))+del3*sin(3*(xli-fasx6));
					xnddt=del1*cos(xli-fasx2)+2*del2*cos(2*(xli-fasx4))+3*del3*cos(3*(xli-fasx6));
				}

				else
				{
					xomi=omegaq+deep_arg->omgdot*atime;
					x2omi=xomi+xomi;
					x2li=xli+xli;
					xndot=d2201*sin(x2omi+xli-g22)+d2211*sin(xli-g22)+d3210*sin(xomi+xli-g32)+d3222*sin(-xomi+xli-g32)+d4410*sin(x2omi+x2li-g44)+d4422*sin(x2li-g44)+d5220*sin(xomi+xli-g52)+d5232*sin(-xomi+xli-g52)+d5421*sin(xomi+x2li-g54)+d5433*sin(-xomi+x2li-g54);
					xnddt=d2201*cos(x2omi+xli-g22)+d2211*cos(xli-g22)+d3210*cos(xomi+xli-g32)+d3222*cos(-xomi+xli-g32)+d5220*cos(xomi+xli-g52)+d5232*cos(-xomi+xli-g52)+2*(d4410*cos(x2omi+x2li-g44)+d4422*cos(x2li-g44)+d5421*cos(xomi+x2li-g54)+d5433*cos(-xomi+x2li-g54));
				}

				xldot=xni+xfact;
				xnddt=xnddt*xldot;

				if (isFlagSet(DO_LOOP_FLAG))
				{
					xli=xli+xldot*delt+xndot*step2;
					xni=xni+xndot*delt+xnddt*step2;
					atime=atime+delt;
				}
			} while (isFlagSet(DO_LOOP_FLAG) && isFlagClear(EPOCH_RESTART_FLAG));
		} while (isFlagSet(DO_LOOP_FLAG) && isFlagSet(EPOCH_RESTART_FLAG));

		deep_arg->xn=xni+xndot*ft+xnddt*ft*ft*0.5;
		xl=xli+xldot*ft+xndot*ft*ft*0.5;
		temp=-deep_arg->xnode+thgr+deep_arg->t*thdt;

		if (isFlagClear(SYNCHRONOUS_FLAG))
		{
			deep_arg->xll=xl+temp+temp;
		}
   		else
		{
			deep_arg->xll=xl-deep_arg->omgadf+temp;
		}

		return;

		case dpper:	 /* Entrance for lunar-solar periodics */
		sinis=sin(deep_arg->xinc);
		cosis=cos(deep_arg->xinc);

		if (fabs(savtsn-deep_arg->t)>=30)
		{
			savtsn=deep_arg->t;
			zm=zmos+zns*deep_arg->t;
			zf=zm+2*zes*sin(zm);
			sinzf=sin(zf);
			f2=0.5*sinzf*sinzf-0.25;
			f3=-0.5*sinzf*cos(zf);
			ses=se2*f2+se3*f3;
			sis=si2*f2+si3*f3;
			sls=sl2*f2+sl3*f3+sl4*sinzf;
			sghs=sgh2*f2+sgh3*f3+sgh4*sinzf;
			shs=sh2*f2+sh3*f3;
			zm=zmol+znl*deep_arg->t;
			zf=zm+2*zel*sin(zm);
			sinzf=sin(zf);
			f2=0.5*sinzf*sinzf-0.25;
			f3=-0.5*sinzf*cos(zf);
			sel=ee2*f2+e3*f3;
			sil=xi2*f2+xi3*f3;
			sll=xl2*f2+xl3*f3+xl4*sinzf;
			sghl=xgh2*f2+xgh3*f3+xgh4*sinzf;
			sh1=xh2*f2+xh3*f3;
			pe=ses+sel;
			pinc=sis+sil;
			pl=sls+sll;
		}

		pgh=sghs+sghl;
		ph=shs+sh1;
		deep_arg->xinc=deep_arg->xinc+pinc;
		deep_arg->em=deep_arg->em+pe;

		if (xqncl>=0.2)
		{
			/* Apply periodics directly */
			ph=ph/deep_arg->sinio;
			pgh=pgh-deep_arg->cosio*ph;
			deep_arg->omgadf=deep_arg->omgadf+pgh;
			deep_arg->xnode=deep_arg->xnode+ph;
			deep_arg->xll=deep_arg->xll+pl;
		}

		else
		{
			/* Apply periodics with Lyddane modification */
			sinok=sin(deep_arg->xnode);
			cosok=cos(deep_arg->xnode);
			alfdp=sinis*sinok;
			betdp=sinis*cosok;
			dalf=ph*cosok+pinc*cosis*sinok;
			dbet=-ph*sinok+pinc*cosis*cosok;
			alfdp=alfdp+dalf;
			betdp=betdp+dbet;
			deep_arg->xnode=FMod2p(deep_arg->xnode);
			xls=deep_arg->xll+deep_arg->omgadf+cosis*deep_arg->xnode;
			dls=pl+pgh-pinc*deep_arg->xnode*sinis;
			xls=xls+dls;
			xnoh=deep_arg->xnode;
			deep_arg->xnode=AcTan(alfdp,betdp);

			/* This is a patch to Lyddane modification */
			/* suggested by Rob Matson. */

			if (fabs(xnoh-deep_arg->xnode)>pi)
			{
				if (deep_arg->xnode<xnoh)
				{
					deep_arg->xnode+=twopi;
				}
				else
				{
					deep_arg->xnode-=twopi;
				}
			}

			deep_arg->xll=deep_arg->xll+pl;
			deep_arg->omgadf=xls-deep_arg->xll-cos(deep_arg->xinc)*deep_arg->xnode;
		}
		return;
	}
}

void SDP4(double tsince, tle_t * tle, vector_t * pos, vector_t * vel)
{
	/* This function is used to calculate the position and velocity */
	/* of deep-space (period > 225 minutes) satellites. tsince is   */
	/* time since epoch in minutes, tle is a pointer to a tle_t     */
	/* structure with Keplerian orbital elements and pos and vel    */
	/* are vector_t structures returning ECI satellite position and */
	/* velocity. Use Convert_Sat_State() to convert to km and km/s. */

	int i;

	static double x3thm1, c1, x1mth2, c4, xnodcf, t2cof, xlcof,
	aycof, x7thm1;

	double a, axn, ayn, aynl, beta, betal, capu, cos2u, cosepw, cosik,
	cosnok, cosu, cosuk, ecose, elsq, epw, esine, pl, theta4, rdot,
	rdotk, rfdot, rfdotk, rk, sin2u, sinepw, sinik, sinnok, sinu,
	sinuk, tempe, templ, tsq, u, uk, ux, uy, uz, vx, vy, vz, xinck, xl,
	xlt, xmam, xmdf, xmx, xmy, xnoddf, xnodek, xll, a1, a3ovk2, ao, c2,
	coef, coef1, x1m5th, xhdot1, del1, r, delo, eeta, eta, etasq,
	perigee, psisq, tsi, qoms24, s4, pinvsq, temp, tempa, temp1,
	temp2, temp3, temp4, temp5, temp6, bx, by, bz, cx, cy, cz;

	static deep_arg_t deep_arg;

	/* Initialization */

	if (isFlagClear(SDP4_INITIALIZED_FLAG))
	{
		SetFlag(SDP4_INITIALIZED_FLAG);

		/* Recover original mean motion (xnodp) and   */
		/* semimajor axis (aodp) from input elements. */

		a1=pow(xke/tle->xno,tothrd);
		deep_arg.cosio=cos(tle->xincl);
		deep_arg.theta2=deep_arg.cosio*deep_arg.cosio;
		x3thm1=3*deep_arg.theta2-1;
		deep_arg.eosq=tle->eo*tle->eo;
		deep_arg.betao2=1-deep_arg.eosq;
		deep_arg.betao=sqrt(deep_arg.betao2);
		del1=1.5*ck2*x3thm1/(a1*a1*deep_arg.betao*deep_arg.betao2);
		ao=a1*(1-del1*(0.5*tothrd+del1*(1+134/81*del1)));
		delo=1.5*ck2*x3thm1/(ao*ao*deep_arg.betao*deep_arg.betao2);
		deep_arg.xnodp=tle->xno/(1+delo);
		deep_arg.aodp=ao/(1-delo);

		/* For perigee below 156 km, the values */
		/* of s and qoms2t are altered.         */

		s4=s;
		qoms24=qoms2t;
		perigee=(deep_arg.aodp*(1-tle->eo)-ae)*xkmper;

		if (perigee<156.0)
		{
			if (perigee<=98.0)
			{
				s4=20.0;
			}
			else
			{
				s4=perigee-78.0;
			}

			qoms24=pow((120-s4)*ae/xkmper,4);
			s4=s4/xkmper+ae;
		}

		pinvsq=1/(deep_arg.aodp*deep_arg.aodp*deep_arg.betao2*deep_arg.betao2);
		deep_arg.sing=sin(tle->omegao);
		deep_arg.cosg=cos(tle->omegao);
		tsi=1/(deep_arg.aodp-s4);
		eta=deep_arg.aodp*tle->eo*tsi;
		etasq=eta*eta;
		eeta=tle->eo*eta;
		psisq=fabs(1-etasq);
		coef=qoms24*pow(tsi,4);
		coef1=coef/pow(psisq,3.5);
		c2=coef1*deep_arg.xnodp*(deep_arg.aodp*(1+1.5*etasq+eeta*(4+etasq))+0.75*ck2*tsi/psisq*x3thm1*(8+3*etasq*(8+etasq)));
		c1=tle->bstar*c2;
		deep_arg.sinio=sin(tle->xincl);
		a3ovk2=-xj3/ck2*pow(ae,3);
		x1mth2=1-deep_arg.theta2;
		c4=2*deep_arg.xnodp*coef1*deep_arg.aodp*deep_arg.betao2*(eta*(2+0.5*etasq)+tle->eo*(0.5+2*etasq)-2*ck2*tsi/(deep_arg.aodp*psisq)*(-3*x3thm1*(1-2*eeta+etasq*(1.5-0.5*eeta))+0.75*x1mth2*(2*etasq-eeta*(1+etasq))*cos(2*tle->omegao)));
		theta4=deep_arg.theta2*deep_arg.theta2;
		temp1=3*ck2*pinvsq*deep_arg.xnodp;
		temp2=temp1*ck2*pinvsq;
		temp3=1.25*ck4*pinvsq*pinvsq*deep_arg.xnodp;
		deep_arg.xmdot=deep_arg.xnodp+0.5*temp1*deep_arg.betao*x3thm1+0.0625*temp2*deep_arg.betao*(13-78*deep_arg.theta2+137*theta4);
		x1m5th=1-5*deep_arg.theta2;
		deep_arg.omgdot=-0.5*temp1*x1m5th+0.0625*temp2*(7-114*deep_arg.theta2+395*theta4)+temp3*(3-36*deep_arg.theta2+49*theta4);
		xhdot1=-temp1*deep_arg.cosio;
		deep_arg.xnodot=xhdot1+(0.5*temp2*(4-19*deep_arg.theta2)+2*temp3*(3-7*deep_arg.theta2))*deep_arg.cosio;
		xnodcf=3.5*deep_arg.betao2*xhdot1*c1;
		t2cof=1.5*c1;
		xlcof=0.125*a3ovk2*deep_arg.sinio*(3+5*deep_arg.cosio)/(1+deep_arg.cosio);
		aycof=0.25*a3ovk2*deep_arg.sinio;
		x7thm1=7*deep_arg.theta2-1;

		/* initialize Deep() */

		Deep(dpinit,tle,&deep_arg);
	}

	/* Update for secular gravity and atmospheric drag */
	xmdf=tle->xmo+deep_arg.xmdot*tsince;
	deep_arg.omgadf=tle->omegao+deep_arg.omgdot*tsince;
	xnoddf=tle->xnodeo+deep_arg.xnodot*tsince;
	tsq=tsince*tsince;
	deep_arg.xnode=xnoddf+xnodcf*tsq;
	tempa=1-c1*tsince;
	tempe=tle->bstar*c4*tsince;
	templ=t2cof*tsq;
	deep_arg.xn=deep_arg.xnodp;

	/* Update for deep-space secular effects */
	deep_arg.xll=xmdf;
	deep_arg.t=tsince;

	Deep(dpsec, tle, &deep_arg);

	xmdf=deep_arg.xll;
	a=pow(xke/deep_arg.xn,tothrd)*tempa*tempa;
	deep_arg.em=deep_arg.em-tempe;
	xmam=xmdf+deep_arg.xnodp*templ;

	/* Update for deep-space periodic effects */
	deep_arg.xll=xmam;

	Deep(dpper,tle,&deep_arg);

	xmam=deep_arg.xll;
	xl=xmam+deep_arg.omgadf+deep_arg.xnode;
	beta=sqrt(1-deep_arg.em*deep_arg.em);
	deep_arg.xn=xke/pow(a,1.5);

	/* Long period periodics */
	axn=deep_arg.em*cos(deep_arg.omgadf);
	temp=1/(a*beta*beta);
	xll=temp*xlcof*axn;
	aynl=temp*aycof;
	xlt=xl+xll;
	ayn=deep_arg.em*sin(deep_arg.omgadf)+aynl;

	/* Solve Kepler's Equation */
	capu=FMod2p(xlt-deep_arg.xnode);
	temp2=capu;
	i=0;

	do
	{
		sinepw=sin(temp2);
		cosepw=cos(temp2);
		temp3=axn*sinepw;
		temp4=ayn*cosepw;
		temp5=axn*cosepw;
		temp6=ayn*sinepw;
		epw=(capu-temp4+temp3-temp2)/(1-temp5-temp6)+temp2;

		if (fabs(epw-temp2)<=e6a)
		{
			break;
		}

		temp2=epw;

	} while (i++<10);

	/* Short period preliminary quantities */
	ecose=temp5+temp6;
	esine=temp3-temp4;
	elsq=axn*axn+ayn*ayn;
	temp=1-elsq;
	pl=a*temp;
	r=a*(1-ecose);
	temp1=1/r;
	rdot=xke*sqrt(a)*esine*temp1;
	rfdot=xke*sqrt(pl)*temp1;
	temp2=a*temp1;
	betal=sqrt(temp);
	temp3=1/(1+betal);
	cosu=temp2*(cosepw-axn+ayn*esine*temp3);
	sinu=temp2*(sinepw-ayn-axn*esine*temp3);
	u=AcTan(sinu,cosu);
	sin2u=2*sinu*cosu;
	cos2u=2*cosu*cosu-1;
	temp=1/pl;
	temp1=ck2*temp;
	temp2=temp1*temp;

	/* Update for short periodics */
	rk=r*(1-1.5*temp2*betal*x3thm1)+0.5*temp1*x1mth2*cos2u;
	uk=u-0.25*temp2*x7thm1*sin2u;
	xnodek=deep_arg.xnode+1.5*temp2*deep_arg.cosio*sin2u;
	xinck=deep_arg.xinc+1.5*temp2*deep_arg.cosio*deep_arg.sinio*cos2u;
	rdotk=rdot-deep_arg.xn*temp1*x1mth2*sin2u;
	rfdotk=rfdot+deep_arg.xn*temp1*(x1mth2*cos2u+1.5*x3thm1);

	/* Orientation vectors */
	sinuk=sin(uk);
	cosuk=cos(uk);
	sinik=sin(xinck);
	cosik=cos(xinck);
	sinnok=sin(xnodek);
	cosnok=cos(xnodek);
	xmx=-sinnok*cosik;
	xmy=cosnok*cosik;
	ux=xmx*sinuk+cosnok*cosuk;
	uy=xmy*sinuk+sinnok*cosuk;
	uz=sinik*sinuk;
	vx=xmx*cosuk-cosnok*sinuk;
	vy=xmy*cosuk-sinnok*sinuk;
	vz=sinik*cosuk;

	/* Position and velocity */
	pos->x=rk*ux;
	pos->y=rk*uy;
	pos->z=rk*uz;
	vel->x=rdotk*ux+rfdotk*vx;
	vel->y=rdotk*uy+rfdotk*vy;
	vel->z=rdotk*uz+rfdotk*vz;

	/* Calculations for squint angle begin here... */

	if (calc_squint)
	{
		bx=cos(alat)*cos(alon+deep_arg.omgadf);
		by=cos(alat)*sin(alon+deep_arg.omgadf);
		bz=sin(alat);
		cx=bx;
		cy=by*cos(xinck)-bz*sin(xinck);
		cz=by*sin(xinck)+bz*cos(xinck);
		ax=cx*cos(xnodek)-cy*sin(xnodek);
		ay=cx*sin(xnodek)+cy*cos(xnodek);
		az=cz;
	}

	/* Phase in radians */
	phase=xlt-deep_arg.xnode-deep_arg.omgadf+twopi;

	if (phase<0.0)
	{
		phase+=twopi;
	}

	phase=FMod2p(phase);
}

void Calculate_User_PosVel(double time, geodetic_t *geodetic, vector_t *obs_pos, vector_t *obs_vel)
{
	/* Calculate_User_PosVel() passes the user's geodetic position
	   and the time of interest and returns the ECI position and
	   velocity of the observer.  The velocity calculation assumes
	   the geodetic position is stationary relative to the earth's
	   surface. */

	/* Reference:  The 1992 Astronomical Almanac, page K11. */

	double c, sq, achcp;

	geodetic->theta=FMod2p(ThetaG_JD(time)+geodetic->lon); /* LMST */
	c=1/sqrt(1+f*(f-2)*Sqr(sin(geodetic->lat)));
	sq=Sqr(1-f)*c;
	achcp=(xkmper*c+geodetic->alt)*cos(geodetic->lat);
	obs_pos->x=achcp*cos(geodetic->theta); /* kilometers */
	obs_pos->y=achcp*sin(geodetic->theta);
	obs_pos->z=(xkmper*sq+geodetic->alt)*sin(geodetic->lat);
	obs_vel->x=-mfactor*obs_pos->y; /* kilometers/second */
	obs_vel->y=mfactor*obs_pos->x;
	obs_vel->z=0;
	Magnitude(obs_pos);
	Magnitude(obs_vel);
}

void Calculate_LatLonAlt(double time, vector_t *pos,  geodetic_t *geodetic)
{
	/* Procedure Calculate_LatLonAlt will calculate the geodetic  */
	/* position of an object given its ECI position pos and time. */
	/* It is intended to be used to determine the ground track of */
	/* a satellite.  The calculations  assume the earth to be an  */
	/* oblate spheroid as defined in WGS '72.                     */

	/* Reference:  The 1992 Astronomical Almanac, page K12. */

	double r, e2, phi, c;

	geodetic->theta=AcTan(pos->y,pos->x); /* radians */
	geodetic->lon=FMod2p(geodetic->theta-ThetaG_JD(time)); /* radians */
	r=sqrt(Sqr(pos->x)+Sqr(pos->y));
	e2=f*(2-f);
	geodetic->lat=AcTan(pos->z,r); /* radians */

	do
	{
		phi=geodetic->lat;
		c=1/sqrt(1-e2*Sqr(sin(phi)));
		geodetic->lat=AcTan(pos->z+xkmper*c*e2*sin(phi),r);

	} while (fabs(geodetic->lat-phi)>=1E-10);

	geodetic->alt=r/cos(geodetic->lat)-xkmper*c; /* kilometers */

	if (geodetic->lat>pio2)
	{
		geodetic->lat-=twopi;
	}
}

void Calculate_Obs(double time, vector_t *pos, vector_t *vel, geodetic_t *geodetic, vector_t *obs_set)
{
	/* The procedures Calculate_Obs and Calculate_RADec calculate         */
	/* the *topocentric* coordinates of the object with ECI position,     */
	/* {pos}, and velocity, {vel}, from location {geodetic} at {time}.    */
	/* The {obs_set} returned for Calculate_Obs consists of azimuth,      */
	/* elevation, range, and range rate (in that order) with units of     */
	/* radians, radians, kilometers, and kilometers/second, respectively. */
	/* The WGS '72 geoid is used and the effect of atmospheric refraction */
	/* (under standard temperature and pressure) is incorporated into the */
	/* elevation calculation; the effect of atmospheric refraction on     */
	/* range and range rate has not yet been quantified.                  */

	/* The {obs_set} for Calculate_RADec consists of right ascension and  */
	/* declination (in that order) in radians.  Again, calculations are   */
	/* based on *topocentric* position using the WGS '72 geoid and        */
	/* incorporating atmospheric refraction.                              */

	double sin_lat, cos_lat, sin_theta, cos_theta, el, azim, top_s, top_e, top_z;

	vector_t obs_pos, obs_vel, range, rgvel;

	Calculate_User_PosVel(time, geodetic, &obs_pos, &obs_vel);

	range.x=pos->x-obs_pos.x;
	range.y=pos->y-obs_pos.y;
	range.z=pos->z-obs_pos.z;

	/* Save these values globally for calculating squint angles later... */

	rx=range.x;
	ry=range.y;
	rz=range.z;

	rgvel.x=vel->x-obs_vel.x;
	rgvel.y=vel->y-obs_vel.y;
	rgvel.z=vel->z-obs_vel.z;

	Magnitude(&range);

	sin_lat=sin(geodetic->lat);
	cos_lat=cos(geodetic->lat);
	sin_theta=sin(geodetic->theta);
	cos_theta=cos(geodetic->theta);
	top_s=sin_lat*cos_theta*range.x+sin_lat*sin_theta*range.y-cos_lat*range.z;
	top_e=-sin_theta*range.x+cos_theta*range.y;
	top_z=cos_lat*cos_theta*range.x+cos_lat*sin_theta*range.y+sin_lat*range.z;
	azim=atan(-top_e/top_s); /* Azimuth */

	if (top_s>0.0)
	{
		azim=azim+pi;
	}

	if (azim<0.0)
	{
		azim=azim+twopi;
	}

	el=ArcSin(top_z/range.w);
	obs_set->x=azim;	/* Azimuth (radians)   */
	obs_set->y=el;		/* Elevation (radians) */
	obs_set->z=range.w;	/* Range (kilometers)  */

	/* Range Rate (kilometers/second) */

	obs_set->w=Dot(&range,&rgvel)/range.w;

	/* Corrections for atmospheric refraction */
	/* Reference:  Astronomical Algorithms by Jean Meeus, pp. 101-104    */
	/* Correction is meaningless when apparent elevation is below horizon */

	/*** The following adjustment for
		 atmospheric refraction is bypassed ***/

	/* obs_set->y=obs_set->y+Radians((1.02/tan(Radians(Degrees(el)+10.3/(Degrees(el)+5.11))))/60); */

	obs_set->y=el;

	/**** End bypass ****/

	if (obs_set->y>=0.0)
	{
		SetFlag(VISIBLE_FLAG);
	}
	else
	{
		obs_set->y=el;  /* Reset to true elevation */
		ClearFlag(VISIBLE_FLAG);
	}
}

void Calculate_RADec(double time, vector_t *pos, vector_t *vel, geodetic_t *geodetic, vector_t *obs_set)
{
	/* Reference:  Methods of Orbit Determination by  */
	/*             Pedro Ramon Escobal, pp. 401-402   */

	double	phi, theta, sin_theta, cos_theta, sin_phi, cos_phi, az, el,
		Lxh, Lyh, Lzh, Sx, Ex, Zx, Sy, Ey, Zy, Sz, Ez, Zz, Lx, Ly,
		Lz, cos_delta, sin_alpha, cos_alpha;

	Calculate_Obs(time,pos,vel,geodetic,obs_set);

	az=obs_set->x;
	el=obs_set->y;
	phi=geodetic->lat;
	theta=FMod2p(ThetaG_JD(time)+geodetic->lon);
	sin_theta=sin(theta);
	cos_theta=cos(theta);
	sin_phi=sin(phi);
	cos_phi=cos(phi);
	Lxh=-cos(az)*cos(el);
	Lyh=sin(az)*cos(el);
	Lzh=sin(el);
	Sx=sin_phi*cos_theta;
	Ex=-sin_theta;
	Zx=cos_theta*cos_phi;
	Sy=sin_phi*sin_theta;
	Ey=cos_theta;
	Zy=sin_theta*cos_phi;
	Sz=-cos_phi;
	Ez=0.0;
	Zz=sin_phi;
	Lx=Sx*Lxh+Ex*Lyh+Zx*Lzh;
	Ly=Sy*Lxh+Ey*Lyh+Zy*Lzh;
	Lz=Sz*Lxh+Ez*Lyh+Zz*Lzh;
	obs_set->y=ArcSin(Lz);  /* Declination (radians) */
	cos_delta=sqrt(1.0-Sqr(Lz));
	sin_alpha=Ly/cos_delta;
	cos_alpha=Lx/cos_delta;
	obs_set->x=AcTan(sin_alpha,cos_alpha); /* Right Ascension (radians) */
	obs_set->x=FMod2p(obs_set->x);
}

/* .... SGP4/SDP4 functions end .... */

time_t CurrentTime()
{
	return time(NULL);
}

double FixAngle(double x)
{
	/* This function reduces angles greater than
	   two pi by subtracting two pi from the angle */

	while (x>twopi)
	{
		x-=twopi;
	}

	return x;
}

double PrimeAngle(double x)
{
	/* This function is used in the FindMoon() function. */

	x=x-360.0*floor(x/360.0);
	return x;
}

char *SubString(char *string, char start, char end)
{
	/* This function returns a substring based on the starting
	   and ending positions provided.  It is used heavily in
	   the AutoUpdate function when parsing 2-line element data. */

	unsigned x, y;

	if (end>=start)
	{
		for (x=start, y=0; x<=end && string[x]!=0; x++)
		{
			if (string[x]!=' ')
			{
				temp[y]=string[x];
				y++;
			}
		}

		temp[y]=0;
		return temp;
	}
	else
	{
		return NULL;
	}
}

void CopyString(char *source, char *destination, char start, char end)
{
	/* This function copies elements of the string "source"
	   bounded by "start" and "end" into the string "destination". */

	unsigned j, k=0;

	for (j=start; j<=end; j++)
	{
		if (source[k]!=0)
		{
			destination[j]=source[k];
			k++;
		}
	}
}

char *Abbreviate(char *string, int n)
{
	/* This function returns an abbreviated substring of the original,
	   including a '~' character if a non-blank character is chopped
	   out of the generated substring.  n is the length of the desired
	   substring.  It is used for abbreviating satellite names. */

	strncpy(temp,string,79);

	if (temp[n]!=0 && temp[n]!=32)
	{
		temp[n-2]='~';
		temp[n-1]=temp[strlen(temp)-1];
	}

	temp[n]=0;

	return temp;
}

char KepCheck(char *line1, char *line2)
{
	/* This function scans line 1 and line 2 of a NASA 2-Line element
	   set and returns a 1 if the element set appears to be valid or
	   a 0 if it does not.  If the data survives this torture test,
	   it's a pretty safe bet we're looking at a valid 2-line
	   element set and not just some random text that might pass
	   as orbital data based on a simple checksum calculation alone. */

	int x;
	unsigned sum1, sum2;

	/* Compute checksum for each line */

	for (x=0, sum1=0, sum2=0; x<=67; sum1+=val[(int)line1[x]], sum2+=val[(int)line2[x]], x++);

	/* Perform a "torture test" on the data */

	x=(val[(int)line1[68]]^(sum1%10)) | (val[(int)line2[68]]^(sum2%10)) |
	  (line1[0]^'1')  | (line1[1]^' ')  | (line1[7]^'U')  |
	  (line1[8]^' ')  | (line1[17]^' ') | (line1[23]^'.') |
	  (line1[32]^' ') | (line1[34]^'.') | (line1[43]^' ') |
	  (line1[52]^' ') | (line1[61]^' ') | (line1[62]^'0') |
	  (line1[63]^' ') | (line2[0]^'2')  | (line2[1]^' ')  |
	  (line2[7]^' ')  | (line2[11]^'.') | (line2[16]^' ') |
	  (line2[20]^'.') | (line2[25]^' ') | (line2[33]^' ') |
	  (line2[37]^'.') | (line2[42]^' ') | (line2[46]^'.') |
	  (line2[51]^' ') | (line2[54]^'.') | (line1[2]^line2[2]) |
	  (line1[3]^line2[3]) | (line1[4]^line2[4]) |
	  (line1[5]^line2[5]) | (line1[6]^line2[6]) |
	  (isdigit(line1[68]) ? 0 : 1) | (isdigit(line2[68]) ? 0 : 1) |
	  (isdigit(line1[18]) ? 0 : 1) | (isdigit(line1[19]) ? 0 : 1) |
	  (isdigit(line2[31]) ? 0 : 1) | (isdigit(line2[32]) ? 0 : 1);

	return (x ? 0 : 1);
}

void InternalUpdate(int x)
{
	/* Updates data in TLE structure based on
	   line1 and line2 stored in structure. */

	double tempnum;

	strncpy(sat.designator,SubString(sat.line1,9,16),8);
	sat.designator[9]=0;
	sat.catnum=atol(SubString(sat.line1,2,6));
	sat.year=atoi(SubString(sat.line1,18,19));
	sat.refepoch=atof(SubString(sat.line1,20,31));
	tempnum=1.0e-5*atof(SubString(sat.line1,44,49));
	sat.nddot6=tempnum/pow(10.0,(sat.line1[51]-'0'));
	tempnum=1.0e-5*atof(SubString(sat.line1,53,58));
	sat.bstar=tempnum/pow(10.0,(sat.line1[60]-'0'));
	sat.setnum=atol(SubString(sat.line1,64,67));
	sat.incl=atof(SubString(sat.line2,8,15));
	sat.raan=atof(SubString(sat.line2,17,24));
	sat.eccn=1.0e-07*atof(SubString(sat.line2,26,32));
	sat.argper=atof(SubString(sat.line2,34,41));
	sat.meanan=atof(SubString(sat.line2,43,50));
	sat.meanmo=atof(SubString(sat.line2,52,62));
	sat.drag=atof(SubString(sat.line1,33,42));
	sat.orbitnum=atof(SubString(sat.line2,63,67));
}

char *noradEvalue(double value)
{
	/* Converts numeric values to E notation used in NORAD TLEs */

	char string[15];

	sprintf(string,"%11.4e",value*10.0);

	output[0]=string[0];
	output[1]=string[1];
	output[2]=string[3];
	output[3]=string[4];
	output[4]=string[5];
	output[5]=string[6];
	output[6]='-';
	output[7]=string[10];
	output[8]=0;

	return output;
}

void Data2TLE(int x)
{
	/* This function converts orbital data held in the numeric
	   portion of the sat tle structure to ASCII TLE format,
	   and places the result in ASCII portion of the structure. */

	int i;
	char string[15], line1[70], line2[70];
	unsigned sum;

	/* Fill lines with blanks */

	for (i=0; i<70; line1[i]=32, line2[i]=32, i++);

	line1[69]=0;
	line2[69]=0;

	/* Insert static characters */

	line1[0]='1';
	line1[7]='U'; /* Unclassified */
	line2[0]='2';

	line1[62]='0'; /* For publically released TLEs */

	/* Insert orbital data */

	sprintf(string,"%05ld",sat.catnum);
	CopyString(string,line1,2,6);
	CopyString(string,line2,2,6);

	CopyString(sat.designator,line1,9,16);

	sprintf(string,"%02d",sat.year);
	CopyString(string,line1,18,19);

	sprintf(string,"%12.8f",sat.refepoch);
	CopyString(string,line1,20,32);

	sprintf(string,"%.9f",fabs(sat.drag));

	CopyString(string,line1,33,42);

	if (sat.drag<0.0)
	{
		line1[33]='-';
	}
	else
	{
		line1[33]=32;
	}

	CopyString(noradEvalue(sat.nddot6),line1,44,51);
	CopyString(noradEvalue(sat.bstar),line1,53,60);

	sprintf(string,"%4lu",sat.setnum);
	CopyString(string,line1,64,67);

	sprintf(string,"%9.4f",sat.incl);
	CopyString(string,line2,7,15);

	sprintf(string,"%9.4f",sat.raan);
	CopyString(string,line2,16,24);

	sprintf(string,"%13.12f",sat.eccn);

	/* Erase eccentricity's decimal point */

	for (i=2; i<=9; string[i-2]=string[i], i++);

	CopyString(string,line2,26,32);

	sprintf(string,"%9.4f",sat.argper);
	CopyString(string,line2,33,41);

	sprintf(string,"%9.5f",sat.meanan);
	CopyString(string,line2,43,50);

	sprintf(string,"%12.9f",sat.meanmo);
	CopyString(string,line2,52,62);

	sprintf(string,"%5lu",sat.orbitnum);
	CopyString(string,line2,63,67);

	/* Compute and insert checksum for line 1 and line 2 */

	for (i=0, sum=0; i<=67; sum+=val[(int)line1[i]], i++);

	line1[68]=(sum%10)+'0';

	for (i=0, sum=0; i<=67; sum+=val[(int)line2[i]], i++);

	line2[68]=(sum%10)+'0';

	line1[69]=0;
	line2[69]=0;

	strcpy(sat.line1,line1);
	strcpy(sat.line2,line2);
}

double ReadBearing(char *input)
{
	/* This function takes numeric input in the form of a character
	   string, and returns an equivalent bearing in degrees as a
	   decimal number (double).  The input may either be expressed
	   in decimal format (74.2467) or degree, minute, second
	   format (74 14 48).  This function also safely handles
	   extra spaces found either leading, trailing, or
	   embedded within the numbers expressed in the
	   input string.  Decimal seconds are permitted. */

	char string[20];
	double bearing=0.0, seconds;
	int a, b, length, degrees, minutes;

	/* Copy "input" to "string", and ignore any extra
	   spaces that might be present in the process. */

	string[0]=0;
	length=strlen(input);

	for (a=0, b=0; a<length && a<18; a++)
	{
		if ((input[a]!=32 && input[a]!='\n') || (input[a]==32 && input[a+1]!=32 && b!=0))
		{
			string[b]=input[a];
			b++;
		}
	}

	string[b]=0;

	/* Count number of spaces in the clean string. */

	length=strlen(string);

	for (a=0, b=0; a<length; a++)
	{
		if (string[a]==32)
		{
			b++;
		}
	}

	if (b==0)  /* Decimal Format (74.2467) */
	{
		sscanf(string,"%lf",&bearing);
	}

	if (b==2)  /* Degree, Minute, Second Format (74 14 48) */
	{
		sscanf(string,"%d %d %lf",&degrees, &minutes, &seconds);

		if (degrees<0.0)
		{
			minutes=-minutes;
			seconds=-seconds;
		}

		bearing=(double)degrees+((double)minutes/60)+(seconds/3600);
	}

	/* Bizarre results return a 0.0 */

	if (bearing>360.0 || bearing<-360.0)
	{
		bearing=0.0;
	}

	return bearing;
}

char ReadTLE(char *line0, char *line1, char *line2)
{
	int la, lb, lc;
	char error_flags,a,b,c,d;

	la = strnlen(line0,sizeof(sat.name));
	lb = strnlen(line1,sizeof(sat.line1));
	lc = strnlen(line2,sizeof(sat.line2));
	a = ((la == 0) || (la >= sizeof(sat.name)));
	b = ((lb == 0) || (lb >= sizeof(sat.line1)));
	c = ((lc == 0) || (lc >= sizeof(sat.line2)));
	d = !KepCheck(line1, line2);
	error_flags = (a << 3) | (b << 2) | (c << 1) | (d << 0);

	if (error_flags == 0)
	{
		strncpy(sat.name,line0,sizeof(sat.name)-1);
		strncpy(sat.line1,line1,sizeof(sat.line1)-1);
		strncpy(sat.line2,line2,sizeof(sat.line2)-1);
		InternalUpdate(0);
	}

	return error_flags;
}

char ReadQTH(double lat, double lon, long alt)
{
	//TODO: add sanity checks
	qth.stnlat = lat;
	qth.stnlong = lon;
	qth.stnalt = alt;

	obs_geodetic.lat=qth.stnlat*deg2rad;
	obs_geodetic.lon=-qth.stnlong*deg2rad;
	obs_geodetic.alt=((double)qth.stnalt)/1000.0;
	obs_geodetic.theta=0.0;

	return 0;
}


char ReadQTHFile()
{
	FILE *fd;

	fd=fopen(qthfile,"r");
	if (fd!=NULL)
	{
		fgets(qth.callsign,16,fd);
		qth.callsign[strlen(qth.callsign)-1]=0;
		fscanf(fd,"%lf", &qth.stnlat);
		fscanf(fd,"%lf", &qth.stnlong);
		fscanf(fd,"%d", &qth.stnalt);
		fclose(fd);

		obs_geodetic.lat=qth.stnlat*deg2rad;
		obs_geodetic.lon=-qth.stnlong*deg2rad;
		obs_geodetic.alt=((double)qth.stnalt)/1000.0;
		obs_geodetic.theta=0.0;
		return 0;
	}
	return -1;
}

char CopyFile(char *source, char *destination)
{
	/* This function copies file "source" to file "destination"
	   in 64k chunks.  The permissions on the destination file
	   are set to rw-r--r--  (0644).  A 0 is returned if no
	   errors are encountered.  A 1 indicates a problem writing
	   to the destination file.  A 2 indicates a problem reading
	   the source file.  */

	int x, sd, dd;
	char error=0, buffer[65536];

	sd=open(source,O_RDONLY);

	if (sd!=-1)
	{
		dd=open(destination,O_WRONLY | O_CREAT| O_TRUNC, 0644);

		if (dd!=-1)
		{
			x=read(sd,&buffer,65536);

			while (x)
			{
				write(dd,&buffer,x);
				x=read(sd,&buffer,65536);
			}

			close(dd);
		}
		else
		{
			error=1;
		}

		close(sd);
	}
	else
	{
		error+=2;
	}

	return error;
}

void SaveQTH()
{
	/* This function saves QTH data to the QTH data file. */

	FILE *fd;

	fd=fopen(qthfile,"w");

	fprintf(fd,"%s\n",qth.callsign);
	fprintf(fd," %g\n",qth.stnlat);
	fprintf(fd," %g\n",qth.stnlong);
	fprintf(fd," %d\n",qth.stnalt);

	fclose(fd);
}

void SaveTLE()
{
	FILE *fd;

 	/* Save orbital data to tlefile */

	fd=fopen(tlefile,"w");

	Data2TLE(0);

	/* Write name, line1, line2 to predict.tle */

	fprintf(fd,"%s\n", sat.name);
	fprintf(fd,"%s\n", sat.line1);
	fprintf(fd,"%s\n", sat.line2);

	fclose(fd);
}

long DayNum(int m, int d, int y)
{
	/* This function calculates the day number from m/d/y. */

	long dn;
	double mm, yy;

	if (m<3)
	{
		y--;
		m+=12;
	}

	if (y<57)
	{
		y+=100;
	}

	yy=(double)y;
	mm=(double)m;
	dn=(long)(floor(365.25*(yy-80.0))-floor(19.0+yy/100.0)+floor(4.75+yy/400.0)-16.0);
	dn+=d+30*m+(long)floor(0.6*mm-0.3);
	return dn;
}

double CurrentDaynum()
{
	/* Read the system clock and return the number
	   of days since 31Dec79 00:00:00 UTC (daynum 0) */
	int x;
	struct timeval tptr;
	double usecs, seconds;

	x=gettimeofday(&tptr,NULL);

	usecs=0.000001*(double)tptr.tv_usec;
	seconds=usecs+(double)tptr.tv_sec;

	return ((seconds/86400.0)-3651.0);
}

void FindMoon(double daynum)
{
	/* This function determines the position of the moon, including
	   the azimuth and elevation headings, relative to the latitude
	   and longitude of the tracking station.  This code was derived
	   from a Javascript implementation of the Meeus method for
	   determining the exact position of the Moon found at:
	   http://www.geocities.com/s_perona/ingles/poslun.htm. */

	double	jd, ss, t, t1, t2, t3, d, ff, l1, m, m1, ex, om, l,
		b, w1, w2, bt, p, lm, h, ra, dec, z, ob, n, e, el,
		az, teg, th, mm, dv;

	jd=daynum+2444238.5;

	t=(jd-2415020.0)/36525.0;
	t2=t*t;
	t3=t2*t;
	l1=270.434164+481267.8831*t-0.001133*t2+0.0000019*t3;
	m=358.475833+35999.0498*t-0.00015*t2-0.0000033*t3;
	m1=296.104608+477198.8491*t+0.009192*t2+0.0000144*t3;
	d=350.737486+445267.1142*t-0.001436*t2+0.0000019*t3;
	ff=11.250889+483202.0251*t-0.003211*t2-0.0000003*t3;
	om=259.183275-1934.142*t+0.002078*t2+0.0000022*t3;
	om=om*deg2rad;

	/* Additive terms */

	l1=l1+0.000233*sin((51.2+20.2*t)*deg2rad);
	ss=0.003964*sin((346.56+132.87*t-0.0091731*t2)*deg2rad);
	l1=l1+ss+0.001964*sin(om);
	m=m-0.001778*sin((51.2+20.2*t)*deg2rad);
	m1=m1+0.000817*sin((51.2+20.2*t)*deg2rad);
	m1=m1+ss+0.002541*sin(om);
	d=d+0.002011*sin((51.2+20.2*t)*deg2rad);
	d=d+ss+0.001964*sin(om);
	ff=ff+ss-0.024691*sin(om);
	ff=ff-0.004328*sin(om+(275.05-2.3*t)*deg2rad);
	ex=1.0-0.002495*t-0.00000752*t2;
	om=om*deg2rad;

	l1=PrimeAngle(l1);
	m=PrimeAngle(m);
	m1=PrimeAngle(m1);
	d=PrimeAngle(d);
	ff=PrimeAngle(ff);
	om=PrimeAngle(om);

	m=m*deg2rad;
	m1=m1*deg2rad;
	d=d*deg2rad;
	ff=ff*deg2rad;

	/* Ecliptic Longitude */

	l=l1+6.28875*sin(m1)+1.274018*sin(2.0*d-m1)+0.658309*sin(2.0*d);
	l=l+0.213616*sin(2.0*m1)-ex*0.185596*sin(m)-0.114336*sin(2.0*ff);
	l=l+0.058793*sin(2.0*d-2.0*m1)+ex*0.057212*sin(2.0*d-m-m1)+0.05332*sin(2.0*d+m1);
	l=l+ex*0.045874*sin(2.0*d-m)+ex*0.041024*sin(m1-m)-0.034718*sin(d);
	l=l-ex*0.030465*sin(m+m1)+0.015326*sin(2.0*d-2.0*ff)-0.012528*sin(2.0*ff+m1);

	l=l-0.01098*sin(2.0*ff-m1)+0.010674*sin(4.0*d-m1)+0.010034*sin(3.0*m1);
	l=l+0.008548*sin(4.0*d-2.0*m1)-ex*0.00791*sin(m-m1+2.0*d)-ex*0.006783*sin(2.0*d+m);

	l=l+0.005162*sin(m1-d)+ex*0.005*sin(m+d)+ex*0.004049*sin(m1-m+2.0*d);
	l=l+0.003996*sin(2.0*m1+2.0*d)+0.003862*sin(4.0*d)+0.003665*sin(2.0*d-3.0*m1);

	l=l+ex*0.002695*sin(2.0*m1-m)+0.002602*sin(m1-2.0*ff-2.0*d)+ex*0.002396*sin(2.0*d-m-2.0*m1);

	l=l-0.002349*sin(m1+d)+ex*ex*0.002249*sin(2.0*d-2.0*m)-ex*0.002125*sin(2.0*m1+m);

	l=l-ex*ex*0.002079*sin(2.0*m)+ex*ex*0.002059*sin(2.0*d-m1-2.0*m)-0.001773*sin(m1+2.0*d-2.0*ff);

	l=l+ex*0.00122*sin(4.0*d-m-m1)-0.00111*sin(2.0*m1+2.0*ff)+0.000892*sin(m1-3.0*d);

	l=l-ex*0.000811*sin(m+m1+2.0*d)+ex*0.000761*sin(4.0*d-m-2.0*m1)+ex*ex*.000717*sin(m1-2.0*m);

	l=l+ex*ex*0.000704*sin(m1-2.0*m-2.0*d)+ex*0.000693*sin(m-2.0*m1+2.0*d)+ex*0.000598*sin(2.0*d-m-2.0*ff)+0.00055*sin(m1+4.0*d);

	l=l+0.000538*sin(4.0*m1)+ex*0.000521*sin(4.0*d-m)+0.000486*sin(2.0*m1-d);

	l=l-0.001595*sin(2.0*ff+2.0*d);

	/* Ecliptic latitude */

	b=5.128189*sin(ff)+0.280606*sin(m1+ff)+0.277693*sin(m1-ff)+0.173238*sin(2.0*d-ff);
	b=b+0.055413*sin(2.0*d+ff-m1)+0.046272*sin(2.0*d-ff-m1)+0.032573*sin(2.0*d+ff);

	b=b+0.017198*sin(2.0*m1+ff)+9.266999e-03*sin(2.0*d+m1-ff)+0.008823*sin(2.0*m1-ff);
	b=b+ex*0.008247*sin(2.0*d-m-ff)+0.004323*sin(2.0*d-ff-2.0*m1)+0.0042*sin(2.0*d+ff+m1);

	b=b+ex*0.003372*sin(ff-m-2.0*d)+ex*0.002472*sin(2.0*d+ff-m-m1)+ex*0.002222*sin(2.0*d+ff-m);

	b=b+0.002072*sin(2.0*d-ff-m-m1)+ex*0.001877*sin(ff-m+m1)+0.001828*sin(4.0*d-ff-m1);

	b=b-ex*0.001803*sin(ff+m)-0.00175*sin(3.0*ff)+ex*0.00157*sin(m1-m-ff)-0.001487*sin(ff+d)-ex*0.001481*sin(ff+m+m1)+ex*0.001417*sin(ff-m-m1)+ex*0.00135*sin(ff-m)+0.00133*sin(ff-d);

	b=b+0.001106*sin(ff+3.0*m1)+0.00102*sin(4.0*d-ff)+0.000833*sin(ff+4.0*d-m1);

	b=b+0.000781*sin(m1-3.0*ff)+0.00067*sin(ff+4.0*d-2.0*m1)+0.000606*sin(2.0*d-3.0*ff);

	b=b+0.000597*sin(2.0*d+2.0*m1-ff)+ex*0.000492*sin(2.0*d+m1-m-ff)+0.00045*sin(2.0*m1-ff-2.0*d);

	b=b+0.000439*sin(3.0*m1-ff)+0.000423*sin(ff+2.0*d+2.0*m1)+0.000422*sin(2.0*d-ff-3.0*m1);

	b=b-ex*0.000367*sin(m+ff+2.0*d-m1)-ex*0.000353*sin(m+ff+2.0*d)+0.000331*sin(ff+4.0*d);

	b=b+ex*0.000317*sin(2.0*d+ff-m+m1)+ex*ex*0.000306*sin(2.0*d-2.0*m-ff)-0.000283*sin(m1+3.0*ff);

	w1=0.0004664*cos(om*deg2rad);
	w2=0.0000754*cos((om+275.05-2.3*t)*deg2rad);
	bt=b*(1.0-w1-w2);

	/* Parallax calculations */

	p=0.950724+0.051818*cos(m1)+0.009531*cos(2.0*d-m1)+0.007843*cos(2.0*d)+0.002824*cos(2.0*m1)+0.000857*cos(2.0*d+m1)+ex*0.000533*cos(2.0*d-m)+ex*0.000401*cos(2.0*d-m-m1);

	p=p+0.000173*cos(3.0*m1)+0.000167*cos(4.0*d-m1)-ex*0.000111*cos(m)+0.000103*cos(4.0*d-2.0*m1)-0.000084*cos(2.0*m1-2.0*d)-ex*0.000083*cos(2.0*d+m)+0.000079*cos(2.0*d+2.0*m1);

	p=p+0.000072*cos(4.0*d)+ex*0.000064*cos(2.0*d-m+m1)-ex*0.000063*cos(2.0*d+m-m1);

	p=p+ex*0.000041*cos(m+d)+ex*0.000035*cos(2.0*m1-m)-0.000033*cos(3.0*m1-2.0*d);

	p=p-0.00003*cos(m1+d)-0.000029*cos(2.0*ff-2.0*d)-ex*0.000029*cos(2.0*m1+m);

	p=p+ex*ex*0.000026*cos(2.0*d-2.0*m)-0.000023*cos(2.0*ff-2.0*d+m1)+ex*0.000019*cos(4.0*d-m-m1);

	b=bt*deg2rad;
	lm=l*deg2rad;
	moon_dx=3.0/(pi*p);

	/* Semi-diameter calculation */
	/* sem=10800.0*asin(0.272488*p*deg2rad)/pi; */

	/* Convert ecliptic coordinates to equatorial coordinates */

	z=(jd-2415020.5)/365.2422;
	ob=23.452294-(0.46845*z+5.9e-07*z*z)/3600.0;
	ob=ob*deg2rad;
	dec=asin(sin(b)*cos(ob)+cos(b)*sin(ob)*sin(lm));
	ra=acos(cos(b)*cos(lm)/cos(dec));

	if (lm>pi)
	{
		ra=twopi-ra;
	}

	/* ra = right ascension */
	/* dec = declination */

	n=qth.stnlat*deg2rad;    /* North latitude of tracking station */
	e=-qth.stnlong*deg2rad;  /* East longitude of tracking station */

	/* Find siderial time in radians */

	t=(jd-2451545.0)/36525.0;
	teg=280.46061837+360.98564736629*(jd-2451545.0)+(0.000387933*t-t*t/38710000.0)*t;

	while (teg>360.0)
	{
		teg-=360.0;
	}

	th=FixAngle((teg-qth.stnlong)*deg2rad);
	h=th-ra;

	az=atan2(sin(h),cos(h)*sin(n)-tan(dec)*cos(n))+pi;
	el=asin(sin(n)*sin(dec)+cos(n)*cos(dec)*cos(h));

	moon_az=az/deg2rad;
	moon_el=el/deg2rad;

	/* Radial velocity approximation.  This code was derived
	   from "Amateur Radio Software", by John Morris, GM4ANB,
	   published by the RSGB in 1985. */

	mm=FixAngle(1.319238+daynum*0.228027135);  /* mean moon position */
	t2=0.10976;
	t1=mm+t2*sin(mm);
	dv=0.01255*moon_dx*moon_dx*sin(t1)*(1.0+t2*cos(mm));
	dv=dv*4449.0;
	t1=6378.0;
	t2=384401.0;
	t3=t1*t2*(cos(dec)*cos(n)*sin(h));
	t3=t3/sqrt(t2*t2-t2*t1*sin(el));
	moon_dv=dv+t3*0.0753125;

	moon_dec=dec/deg2rad;
	moon_ra=ra/deg2rad;
	moon_gha=teg-moon_ra;

	if (moon_gha<0.0)
	{
		moon_gha+=360.0;
	}
}

void FindSun(double daynum)
{
	/* This function finds the position of the Sun */

	/* Zero vector for initializations */
	vector_t zero_vector={0,0,0,0};

	/* Solar ECI position vector  */
	vector_t solar_vector=zero_vector;

	/* Solar observed azi and ele vector  */
	vector_t solar_set=zero_vector;

	/* Solar right ascension and declination vector */
	vector_t solar_rad=zero_vector;

	/* Solar lat, long, alt vector */
	geodetic_t solar_latlonalt;

	jul_utc=daynum+2444238.5;

	Calculate_Solar_Position(jul_utc, &solar_vector);
	Calculate_Obs(jul_utc, &solar_vector, &zero_vector, &obs_geodetic, &solar_set);
	sun_azi=Degrees(solar_set.x);
	sun_ele=Degrees(solar_set.y);
	sun_range=1.0+((solar_set.z-AU)/AU);
	sun_range_rate=1000.0*solar_set.w;

	Calculate_LatLonAlt(jul_utc, &solar_vector, &solar_latlonalt);

	sun_lat=Degrees(solar_latlonalt.lat);
	sun_lon=360.0-Degrees(solar_latlonalt.lon);

	Calculate_RADec(jul_utc, &solar_vector, &zero_vector, &obs_geodetic, &solar_rad);

	sun_ra=Degrees(solar_rad.x);
	sun_dec=Degrees(solar_rad.y);
}

void PreCalc(int x)
{
	/* This function copies TLE data from PREDICT's sat structure
	   to the SGP4/SDP4's single dimensioned tle structure, and
	   prepares the tracking code for the update. */

	strcpy(tle.sat_name,sat.name);
	strcpy(tle.idesg,sat.designator);
	tle.catnr=sat.catnum;
	tle.epoch=(1000.0*(double)sat.year)+sat.refepoch;
	tle.xndt2o=sat.drag;
	tle.xndd6o=sat.nddot6;
	tle.bstar=sat.bstar;
	tle.xincl=sat.incl;
	tle.xnodeo=sat.raan;
	tle.eo=sat.eccn;
	tle.omegao=sat.argper;
	tle.xmo=sat.meanan;
	tle.xno=sat.meanmo;
	tle.revnum=sat.orbitnum;

	if (sat_db.squintflag)
	{
		calc_squint=1;
		alat=deg2rad*sat_db.alat;
		alon=deg2rad*sat_db.alon;
	}
	else
	{
		calc_squint=0;
	}

	/* Clear all flags */

	ClearFlag(ALL_FLAGS);

	/* Select ephemeris type.  This function will set or clear the
	   DEEP_SPACE_EPHEM_FLAG depending on the TLE parameters of the
	   satellite.  It will also pre-process tle members for the
	   ephemeris functions SGP4 or SDP4, so this function must
	   be called each time a new tle set is used. */

	select_ephemeris(&tle);
}

void Calc()
{
	/* This is the stuff we need to do repetitively while tracking. */

	/* Zero vector for initializations */
	vector_t zero_vector={0,0,0,0};

	/* Satellite position and velocity vectors in ECI */
	vector_t vel=zero_vector;
	vector_t pos=zero_vector;

	/* Observer position and velocity vectors in ECI */
	vector_t obs_pos=zero_vector;
	vector_t obs_vel=zero_vector;

	/* Satellite Az, El, Range, Range rate */
	vector_t obs_set;

	/* Solar ECI position vector  */
	vector_t solar_vector=zero_vector;

	/* Solar observed azi and ele vector  */
	vector_t solar_set;

	/* Orbit normal vector used for calculating beta angle */
	vector_t orbit_n_vector=zero_vector;

	/* Satellite's predicted geodetic position */
	geodetic_t sat_geodetic;

	jul_utc=daynum+2444238.5;

	/* Convert satellite's epoch time to Julian  */
	/* and calculate time since epoch in minutes */

	jul_epoch=Julian_Date_of_Epoch(tle.epoch);
	tsince=(jul_utc-jul_epoch)*xmnpda;
	age=jul_utc-jul_epoch;

	/* Copy the ephemeris type in use to ephem string. */

		if (isFlagSet(DEEP_SPACE_EPHEM_FLAG))
		{
			strcpy(ephem,"SDP4");
		}
		else
		{
			strcpy(ephem,"SGP4");
		}

	/* Call NORAD routines according to deep-space flag. */

	if (isFlagSet(DEEP_SPACE_EPHEM_FLAG))
	{
		SDP4(tsince, &tle, &pos, &vel);
	}
	else
	{
		SGP4(tsince, &tle, &pos, &vel);
	}

	/* Scale position and velocity vectors to km and km/sec */

	Convert_Sat_State(&pos, &vel);

	/* Calculate velocity of satellite */

	Magnitude(&vel);
	sat_vel=vel.w;
	eci_x = pos.x;
	eci_y = pos.y;
	eci_z = pos.z;
	eci_vx = vel.x;
	eci_vy = vel.y;
	eci_vz = vel.z;

	/** All angles in rads. Distance in km. Velocity in km/s **/
	/* Calculate satellite Azi, Ele, Range and Range-rate */

	Calculate_Obs(jul_utc, &pos, &vel, &obs_geodetic, &obs_set);

	Calculate_User_PosVel(jul_utc, &obs_geodetic, &obs_pos, &obs_vel);

	eci_obs_x = obs_pos.x;
	eci_obs_y = obs_pos.y;
	eci_obs_z = obs_pos.z;

	/* Calculate satellite Lat North, Lon East and Alt. */

	Calculate_LatLonAlt(jul_utc, &pos, &sat_geodetic);

	/* Calculate squint angle */

	if (calc_squint)
	{
		squint=(acos(-(ax*rx+ay*ry+az*rz)/obs_set.z))/deg2rad;
	}

	/* Calculate solar position and satellite eclipse depth. */
	/* Also set or clear the satellite eclipsed flag accordingly. */

	Calculate_Solar_Position(jul_utc, &solar_vector);

	eci_sun_x = solar_vector.x;
	eci_sun_y = solar_vector.y;
	eci_sun_z = solar_vector.z;

	Cross(&pos,&vel,&orbit_n_vector);

	beta_angle = (pio2-Angle(&orbit_n_vector,&solar_vector))/deg2rad;

	Calculate_Obs(jul_utc, &solar_vector, &zero_vector, &obs_geodetic, &solar_set);

	if (Sat_Eclipsed(&pos, &solar_vector, &eclipse_depth))
	{
		SetFlag(SAT_ECLIPSED_FLAG);
	}
	else
	{
		ClearFlag(SAT_ECLIPSED_FLAG);
	}

	if (isFlagSet(SAT_ECLIPSED_FLAG))
	{
		sat_sun_status=0;  /* Eclipse */
	}
	else
	{
		sat_sun_status=1; /* In sunlight */
	}

	/* Convert satellite and solar data */
	sat_azi=Degrees(obs_set.x);
	sat_ele=Degrees(obs_set.y);
	sat_range=obs_set.z;
	sat_range_rate=obs_set.w;
	sat_lat=Degrees(sat_geodetic.lat);
	sat_lon=Degrees(sat_geodetic.lon);
	sat_alt=sat_geodetic.alt;

	fk=12756.33*acos(xkmper/(xkmper+sat_alt));
	fm=fk/1.609344;

	rv=(long)floor((tle.xno*xmnpda/twopi+age*tle.bstar*ae)*age+tle.xmo/twopi)+tle.revnum;

	sun_azi=Degrees(solar_set.x);
	sun_ele=Degrees(solar_set.y);

	irk=(long)rint(sat_range);
	isplat=(int)rint(sat_lat);
	isplong=(int)rint(360.0-sat_lon);
	iaz=(int)rint(sat_azi);
	iel=(int)rint(sat_ele);
	ma256=(int)rint(256.0*(phase/twopi));

	if (sat_sun_status)
	{
		if (sun_ele<=-12.0 && rint(sat_ele)>=0.0)
		{
			findsun='+';
		}
		else
		{
			findsun='*';
		}
	}
	else
	{
		findsun=' ';
	}
}

char AosHappens(int x)
{
	/* This function returns a 1 if the satellite pointed to by
	   "x" can ever rise above the horizon of the ground station. */

	double lin, sma, apogee;

	if (sat.meanmo==0.0)
	{
		return 0;
	}
	else
	{
		lin=sat.incl;

		if (lin>=90.0)
		{
			lin=180.0-lin;
		}

		sma=331.25*exp(log(1440.0/sat.meanmo)*(2.0/3.0));
		apogee=sma*(1.0+sat.eccn)-xkmper;

		if ((acos(xkmper/(apogee+xkmper))+(lin*deg2rad)) > fabs(qth.stnlat*deg2rad))
		{
			return 1;
		}
		else
		{
			return 0;
		}
	}
}

char Decayed(int x, double time)
{
	/* This function returns a 1 if it appears that the
	   satellite pointed to by 'x' has decayed at the
	   time of 'time'.  If 'time' is 0.0, then the
	   current date/time is used. */

	double satepoch;

	if (time==0.0)
	{
		time=CurrentDaynum();
	}

	satepoch=DayNum(1,0,sat.year)+sat.refepoch;

	if (satepoch+((16.666666-sat.meanmo)/(10.0*fabs(sat.drag))) < time)
	{
		return 1;
	}
	else
	{
		return 0;
	}
}

char Geostationary(int x)
{
	/* This function returns a 1 if the satellite pointed
	   to by "x" appears to be in a geostationary orbit */

	if (fabs(sat.meanmo-1.0027)<0.0002)
	{
		return 1;
	}
	else
	{
		return 0;
	}
}

double FindAOS()
{
	/* This function finds and returns the time of AOS (aostime). */

	int iterations = 0;
	aostime=0.0;

	if (AosHappens(indx) && Geostationary(indx)==0 && Decayed(indx,daynum)==0)
	{
		Calc();

		/* Get the satellite in range */

		while (sat_ele<-1.0)
		{
			daynum-=0.00035*(sat_ele*((sat_alt/8400.0)+0.46)-2.0);
			Calc();
		}

		/* Find AOS */

		// TODO: FIX: We use a max on iterations here to avoid getting stuck when we no longer have an aos
		while (aostime==0.0 && iterations < 100000)
		{
			if (fabs(sat_ele)<0.03)
			{
				aostime=daynum;
			}
			else
			{
				daynum-=sat_ele*sqrt(sat_alt)/530000.0;
				Calc();
			}
			iterations += 1;
		}
	}

	return aostime;
}

double FindLOS()
{
	lostime=0.0;

	if (Geostationary(indx)==0 && AosHappens(indx)==1 && Decayed(indx,daynum)==0)
	{
		Calc();

		do
		{
			daynum+=sat_ele*sqrt(sat_alt)/502500.0;
			Calc();

			if (fabs(sat_ele) < 0.03)
			{
				lostime=daynum;
			}

		} while (lostime==0.0);
	}

	return lostime;
}

double FindLOS2()
{
	/* This function steps through the pass to find LOS.
	   FindLOS() is called to "fine tune" and return the result. */

	do
	{
		daynum+=cos((sat_ele-1.0)*deg2rad)*sqrt(sat_alt)/25000.0;
		Calc();

	} while (sat_ele>=0.0);

	return(FindLOS());
}

double NextAOS()
{
	/* This function finds and returns the time of the next
	   AOS for a satellite that is currently in range. */

	aostime=0.0;

	if (AosHappens(indx) && Geostationary(indx)==0 && Decayed(indx,daynum)==0)
	{
		daynum=FindLOS2()+0.014;  /* Move to LOS + 20 minutes */
	}

	return (FindAOS());
}

// This function was extracted from SingleTrack and shows a number of derived parameters related
// to a satellite observed from a particular point on earth.
//
// NOTE: We don't support uplink, downlink, squint and related parameters.  The related code
//       is convoluted and it's never come up in our usage.  FYI, the 'Edit Transponder Database'
//       menu option is still marked "coming soon" :).  We'll add it back if there's demand.
//
int MakeObservation(double obs_time, struct observation * obs) {
    char geostationary=0, aoshappens=0, decayed=0, visibility=0, sunlit;
    double doppler100=0.0, delay;

    PreCalc(0);
    indx=0;

    if (sat_db.transponders>0)
    {
        PyErr_SetString(PredictException, "pypredict does not support transponder definition.");
        return -1;
    }

    daynum=obs_time;
    aoshappens=AosHappens(indx);
    geostationary=Geostationary(indx);
    decayed=Decayed(indx,0.0);

    //Calcs
    Calc();
    fk=12756.33*acos(xkmper/(xkmper+sat_alt));

    if (sat_sun_status)
    {
        if (sun_ele<=-12.0 && sat_ele>=0.0) {
            visibility='V';
        } else {
            visibility='D';
        }
    } else {
        visibility='N';
    }
    // gathering power seems much more useful than naked-eye visibility
    sunlit = sat_sun_status;

    doppler100=-100.0e06*((sat_range_rate*1000.0)/299792458.0);
    delay=1000.0*((1000.0*sat_range)/299792458.0);

    //TODO: Seems like FindSun(daynum) should go in here
    FindMoon(daynum);

    //printw(5+tshift,1,"Satellite     Direction     Velocity     Footprint    Altitude     Slant Range");
    //printw(6+tshift,1,"---------     ---------     --------     ---------    --------     -----------");
    //printw(7+tshift,1,"        .            Az           mi            mi          mi              mi");
    //printw(8+tshift,1,"        .            El           km            km          km              km");
    //printw(16+bshift,1,"Eclipse Depth   Orbital Phase   Orbital Model   Squint Angle      AutoTracking");
    //printw(17+bshift,1,"-------------   -------------   -------------   ------------      ------------");

    obs->norad_id = sat.catnum;
    strncpy(&(obs->name), &(sat.name), sizeof(obs->name));
    obs->epoch = (daynum+3651.0)*(86400.0); //See daynum=((start/86400.0)-3651.0);
    obs->latitude = sat_lat;
    obs->longitude = sat_lon;
    obs->azimuth = sat_azi;
    obs->elevation = sat_ele;
    obs->orbital_velocity = 3600.0*sat_vel;
    obs->footprint = fk;
    obs->altitude = sat_alt;
    obs->slant_range = sat_range;
    obs->eclipse_depth = eclipse_depth/deg2rad;
    obs->orbital_phase = 256.0*(phase/twopi);
    strncpy(&(obs->orbital_model), &(ephem), sizeof(obs->orbital_model));
    obs->visibility = visibility;
    obs->sunlit = sunlit;
    obs->orbit = rv;
    obs->geostationary = geostationary;
    obs->has_aos = aoshappens;
    obs->decayed = decayed;
    obs->doppler = doppler100;
    obs->eci_x = eci_x;
    obs->eci_y = eci_y;
    obs->eci_z = eci_z;
    obs->eci_vx = eci_vx;
    obs->eci_vy = eci_vy;
    obs->eci_vz = eci_vz;
    obs->eci_sun_x = eci_sun_x;
    obs->eci_sun_y = eci_sun_y;
    obs->eci_sun_z = eci_sun_z;
    obs->eci_obs_x = eci_obs_x;
    obs->eci_obs_y = eci_obs_y;
    obs->eci_obs_z = eci_obs_z;
    obs->beta_angle = beta_angle;
    return 0;
}

void PrintObservation(struct observation * obs) {
    printf("NORAD_ID        %d\n", obs->norad_id);
    printf("Name            %s\n", obs->name);
    printf("Date(epoch)     %f\n", obs->epoch);
    printf("Latitude(N)     %f\n", obs->latitude);
    printf("Longitude(E)    %f\n", obs->longitude);
    printf("Azimuth         %f\n", obs->azimuth);
    printf("Elevation       %f\n", obs->elevation);
    printf("Velocity        %f\n", obs->orbital_velocity);
    printf("Footprint       %f\n", obs->footprint);
    printf("Altitude(km)    %f\n", obs->altitude);
    printf("Slant_Range(km) %f\n", obs->slant_range);
    printf("Eclipse_Depth   %f\n", obs->eclipse_depth);
    printf("Orbital_Phase   %f\n", obs->orbital_phase);
    printf("Orbital_Model   %s\n", obs->orbital_model);
    printf("Visibility      %c\n", obs->visibility);
    printf("Sunlight        %d\n", obs->sunlit);
    printf("Orbit_Number    %ld\n",obs->orbit);
    printf("Geostationary   %d\n", obs->geostationary);
    printf("AOS_Happens     %d\n", obs->has_aos);
    printf("Decayed         %d\n", obs->decayed);
    printf("Doppler         %f\n", obs->doppler);
    printf("ECI_x           %f\n", obs->eci_x);
    printf("ECI_y           %f\n", obs->eci_y);
    printf("ECI_z           %f\n", obs->eci_z);
    printf("ECI_vx          %f\n", obs->eci_vx);
    printf("ECI_vy          %f\n", obs->eci_vy);
    printf("ECI_vz          %f\n", obs->eci_vz);
    printf("ECI_sun_x       %f\n", obs->eci_sun_x);
    printf("ECI_sun_y       %f\n", obs->eci_sun_y);
    printf("ECI_sun_z       %f\n", obs->eci_sun_z);
    printf("ECI_obs_x       %f\n", obs->eci_obs_x);
    printf("ECI_obs_y       %f\n", obs->eci_obs_y);
    printf("ECI_obs_z       %f\n", obs->eci_obs_z);
    printf("Beta_Angle(deg) %f\n", obs->beta_angle);
}

PyObject * PythonifyObservation(observation * obs) {
	//TODO: Add reference count?
	return Py_BuildValue("{s:l,s:s,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:s,s:c,s:i,s:l,s:i,s:i,s:i,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d}",
		"norad_id", obs->norad_id,
		"name", obs->name,
		"epoch", obs->epoch,
		"latitude", obs->latitude,
		"longitude", obs->longitude,
		"azimuth", obs->azimuth,
		"elevation", obs->elevation,
		"orbital_velocity", obs->orbital_velocity,
		"footprint", obs->footprint,
		"altitude", obs->altitude,
		"slant_range", obs->slant_range,
		"eclipse_depth", obs->eclipse_depth,
		"orbital_phase", obs->orbital_phase,
		"orbital_model", obs->orbital_model,
		"visibility", obs->visibility,
		"sunlit", obs->sunlit,
		"orbit", obs->orbit,
		"geostationary", obs->geostationary,
		"has_aos", obs->has_aos,
		"decayed", obs->decayed,
		"doppler", obs->doppler,
		"eci_x", obs->eci_x,
		"eci_y", obs->eci_y,
		"eci_z", obs->eci_z,
		"eci_vx", obs->eci_vx,
		"eci_vy", obs->eci_vy,
		"eci_vz", obs->eci_vz,
		"eci_sun_x", obs->eci_sun_x,
		"eci_sun_y", obs->eci_sun_y,
		"eci_sun_z", obs->eci_sun_z,
		"eci_obs_x", obs->eci_obs_x,
		"eci_obs_y", obs->eci_obs_y,
		"eci_obs_z", obs->eci_obs_z,
		"beta_angle", obs->beta_angle
	);
}

char load(PyObject *args)
{
	//TODO: Not threadsafe, detect and raise warning?
	int x;
	char *env=NULL;

	/* Set up translation table for computing TLE checksums */
	for (x=0; x<=255; val[x]=0, x++);
	for (x='0'; x<='9'; val[x]=x-'0', x++);

	val['-']=1;

	double epoch;
	const char *tle0, *tle1, *tle2;

	if (!PyArg_ParseTuple(args, "(sss)|d(ddi)",
		&tle0, &tle1, &tle2, &epoch, &qth.stnlat, &qth.stnlong, &qth.stnalt))
	{
		// PyArg_ParseTuple will set appropriate exception string
		return -1;
	};

	if (ReadTLE(tle0,tle1,tle2) != 0)
	{
		PyErr_SetString(PredictException, "Unable to process TLE");
		return -1;
	}

	// If time isn't set, use current time.
	if (PyObject_Length(args) < 2)
	{
		daynum=CurrentDaynum();
	}
	else
	{
		daynum=((epoch/86400.0)-3651.0);
	}

	// If we haven't already set groundstation location, use predict's default.
	if (PyObject_Length(args) < 3)
	{
		FILE *fd;
		env=getenv("HOME");
		sprintf(qthfile,"%s/.predict/predict.qth",env);
		fd=fopen(qthfile,"r");
		if (fd!=NULL)
		{
			fgets(qth.callsign,16,fd);
			qth.callsign[strlen(qth.callsign)-1]=0;
			fscanf(fd,"%lf", &qth.stnlat);
			fscanf(fd,"%lf", &qth.stnlong);
			fscanf(fd,"%d", &qth.stnalt);
			fclose(fd);
		} else {
			PyErr_SetString(PredictException, "QTH file could not be loaded.");
			return -1;
		}
	}
	obs_geodetic.lat=qth.stnlat*deg2rad;
	obs_geodetic.lon=-qth.stnlong*deg2rad;
	obs_geodetic.alt=((double)qth.stnalt)/1000.0;
	obs_geodetic.theta=0.0;

	return 0;
}

static PyObject* quick_find(PyObject* self, PyObject *args)
{
	struct observation obs = { 0 };

	if (load(args) != 0 || MakeObservation(daynum, &obs) != 0)
	{
		// load or MakeObservation will set appropriate exceptions if either fails.
		return NULL;
	}

	return PythonifyObservation(&obs);
}

static char quick_find_docs[] =
    "quick_find((tle_line0, tle_line1, tle_line2), time, (gs_lat, gs_lon, gs_alt))\n";

static PyObject* quick_predict(PyObject* self, PyObject *args)
{
	double tle_epoch;
	int lastel=0;
	char errbuff[100];
	observation obs = { 0 };

	PyObject* transit = PyList_New(0);
	if (transit == NULL)
	{
		goto cleanup_and_raise_exception;
	}

	if (load(args) != 0)
	{
		// load will set the appropriate exception string if it fails.
		goto cleanup_and_raise_exception;
	}

	tle_epoch=(double)DayNum(1,0,sat.year)+sat.refepoch;
	if ((daynum<tle_epoch-365.0) || (daynum>tle_epoch+365.0))
	{
		sprintf(errbuff, "day number %.0f too far from tle epoch day %.0f\n", daynum, tle_epoch);
		PyErr_SetString(PredictException, errbuff);
		goto cleanup_and_raise_exception;
	}

	PreCalc(0);
	Calc();
	if (MakeObservation(daynum, &obs) != 0)
	{
		// MakeObservation will set appropriate exception string
		goto cleanup_and_raise_exception;
	}

	if (!AosHappens(0))
	{
		sprintf(errbuff, "%lu does not rise above horizon. No AOS.\n", sat.catnum);
		PyErr_SetString(NoTransitException, errbuff);
		goto cleanup_and_raise_exception;
	}

	if (Geostationary(0)!=0)
	{
		sprintf(errbuff, "%lu is geostationary.  Does not transit.\n", sat.catnum);
		PyErr_SetString(PredictException, errbuff);
		goto cleanup_and_raise_exception;
	}

	if (Decayed(indx,daynum)!=0)
	{
		sprintf(errbuff, "%lu has decayed. Cannot calculate transit.\n", sat.catnum);
		PyErr_SetString(PredictException, errbuff);
		goto cleanup_and_raise_exception;
	}

	/* Make Predictions */
	daynum=FindAOS();

	if (daynum == 0)
	{
		sprintf(errbuff, "%lu no longer rises above horizon. No AOS.\n", sat.catnum);
		PyErr_SetString(NoTransitException, errbuff);
		goto cleanup_and_raise_exception;
	}

	/* Construct the pass */
	PyObject * py_obs;
	while (iel>=0)
	{
		if (MakeObservation(daynum, &obs) != 0)
		{
			//MakeObservation will set appropriate exception string
			goto cleanup_and_raise_exception;
		}

		py_obs = PythonifyObservation(&obs);
		if (py_obs == NULL) {
			//PythonifyObservation will set appropriate exception string
			goto cleanup_and_raise_exception;
		}

		if (PyList_Append(transit, py_obs) != 0)
		{
			Py_DECREF(py_obs);
			goto cleanup_and_raise_exception;
		}
		Py_DECREF(py_obs);
		lastel=iel;
		daynum+=cos((sat_ele-1.0)*deg2rad)*sqrt(sat_alt)/25000.0;
		Calc();
	}

	if (lastel!=0)
	{
		daynum=FindLOS();
		//TODO: FindLOS can fail.  Detect and log warning that transit end is approximate.
		if (daynum > 0) {
			Calc();

			if (MakeObservation(daynum, &obs) != 0)
			{
				goto cleanup_and_raise_exception;
			}

			py_obs = PythonifyObservation(&obs);
			if (py_obs == NULL) {
				goto cleanup_and_raise_exception;
			}

			if (PyList_Append(transit, py_obs) != 0)
			{
				Py_DECREF(py_obs);
				goto cleanup_and_raise_exception;
			}
			Py_DECREF(py_obs);
		}
	}

	return transit;

cleanup_and_raise_exception:
	Py_XDECREF(transit);
	return NULL;
}

static char quick_predict_docs[] =
    "quick_predict((tle_line0, tle_line1, tle_line2), time, (gs_lat, gs_lon, gs_alt))\n";

static PyMethodDef pypredict_funcs[] = {
    {"quick_find"   , (PyCFunction)quick_find   , METH_VARARGS, quick_find_docs},
    {"quick_predict", (PyCFunction)quick_predict, METH_VARARGS, quick_predict_docs},
    {NULL, NULL, 0, NULL}
};

#if PY_MAJOR_VERSION >= 3
	static struct PyModuleDef moduledef = {
		PyModuleDef_HEAD_INIT,
		"cpredict",     /* m_name */
		"Python port of the predict open source satellite tracking library",  /* m_doc */
		-1,                  /* m_size */
		pypredict_funcs,    /* m_methods */
		NULL,                /* m_reload */
		NULL,                /* m_traverse */
		NULL,                /* m_clear */
		NULL,                /* m_free */
	};
#endif

static PyObject * cpredictinit(void)
{
	PyObject *m;
#if PY_MAJOR_VERSION >= 3
	m = PyModule_Create(&moduledef);
#else
	m = Py_InitModule3("cpredict", pypredict_funcs,
					"Python port of the predict open source satellite tracking library");
#endif
	if (m == NULL) {
		fprintf(stderr, "ERROR: Unable to initialize python module 'cpredict'\n");
	}

	// Add custom base exception for predict
	PredictException = PyErr_NewException("cpredict.PredictException", NULL, NULL);
	Py_INCREF(PredictException);
	PyModule_AddObject(m, "PredictException", PredictException);

	// Specific exception for satellites that don't transit to distinguish from more serious failures
	NoTransitException = PyErr_NewException("cpredict.NoTransitException", PredictException, NULL);
	Py_INCREF(NoTransitException);
	PyModule_AddObject(m, "NoTransitException", NoTransitException);

	return m;
}

#if PY_MAJOR_VERSION >= 3
PyMODINIT_FUNC PyInit_cpredict(void)
{
	return cpredictinit();
}
#else
PyMODINIT_FUNC initcpredict(void)
{
	cpredictinit();
}
#endif