All-sky density mapping

This library implements a all-sky density map builder (C++) and plotter (Python).

Density mapper: radec_density

It allows one to create a density map by streaming data from an Ascii source or STDIN. The streaming features helps reducing the memory footprint to almost nothing even when dealing with large amount of data. Only the density map is fully in memory during the computations (< 1M). The code allows transformation on the fly such as converting inputs in radians to degrees (--radians option) or sky coordinate transformation (--transform option).

For speed reasons, this code is made in C++ (using C++11 features) and do not require external libraries that standard ones.

Tested with gcc 4.8.4 (ubuntu), gcc 5.3 and clang 7.

to compile the code, run: > make

> ./radec_density -h

-h, --help	Display help message
-i, --input	input data file
-o, --output	output histogram to file
-c, --columns	column indexes to use (RA, DEC [,Weight]) (starts at 0)
--dra	RA bin width in degrees
--ddec	RA bin width in degrees
-t, --transform
	coordinate transformation
--comment	comment line character in input file
-d, --delim	delimiter character in input file
-r, --radians	set if input ra,dec are in radians

Available transformations

Using the internal coordinates library, you can transform one set of coordinates into another system. Available transformations are:

name	from	to
GAL2ICRS	galactic	ICRS
ICRS2GAL	ICRS	galactic
ECL2ICRS	ecliptic	ICRS
ICRS2ECL	ICRS	ecliptic
GAL2ECL	galactic	ecliptic
ECL2GAL	ecliptic	galactic

Transformations are based on

Hipparcos Explanatory Vol 1 section 1.5 Murray, 1983, section 10.2 van Altena et al. 2012, Chapter 4.5 of "Astrometry for Astrophysics"

Galactic pole coordinates are based on J2000 values.

Output file

The output file of the code is a plain Ascii array (image)

the axis ranges span the all-sky

x := [-180, 180] and y:= [-90, 90]

with angular pixel sizes given by

dx := 360. / float(nx) and dy := 180. / float(ny)

The plotting code (plot.py) knows already what to do with it.

Plot density map: plot.py

This python code generates a map from the outputs of radec_density. The projection can be defined based on what is available in mpl_toolkits.basemap.

requires mpl_toolkits.basemap

> ./plot.py -h

-h, --help	show this help message and exit
--title=TITLE	Figure title
-o FIGOUT, --output=FIGOUT
	export figures using this suffixe
-q, --quiet	set to skip showing the figures
--projection=PROJECTION
	MAP Coordinate projection base
--log	Set to log-scale the density

Examples

Sample catalog file is included in the repository

> ./radec_density -i sample.cat -o sample_icrs.hist --dra 1 --ddec 1
> ./plot.py sample_icrs.hist --title icrs -o sample_icrs.png
> ./radec_density -i sample.cat -o sample_gal.hist --dra 1 --ddec 1 -t ICRS2GAL
> ./plot.py sample_gal.hist --title galactic -o sample_gal.png