Implements unit tests for orbit conversion utils, fixes obliquity of …

…the ecliptic value
dirac-institute · Dec 13, 2023 · 8d92c03 · 8d92c03
1 parent b9b5cdf
commit 8d92c03
Show file tree

Hide file tree

Showing 3 changed files with 206 additions and 2 deletions.
diff --git a/docs/notebooks/demo_Lightcurve.ipynb b/docs/notebooks/demo_Lightcurve.ipynb
@@ -16,7 +16,7 @@
     "The goal of this notebook is to demonstrate the use of lightcurves within `sorcha`.\n",
     "\n",
     "This will be done in two different ways:\n",
-    "- We will use the community tools part of the [`sorcha_addons`](https://github.com/dirac-institute/sorcha-addons) package\n",
+    "- We will use the community tools part of the [`sorcha-addons`](https://github.com/dirac-institute/sorcha-addons) package\n",
     "- We will implement a custom lightcurve, and use it inside the code\n",
     "\n",
     "The idea is that the user can, in principle, implement their own lightcurves, and incorporate them in their simulation. The goal of `sorcha-addons` is for both the development team, as well as for the community, to share their implementations of custom lightcurve models. "

diff --git a/src/sorcha/ephemeris/simulation_constants.py b/src/sorcha/ephemeris/simulation_constants.py
@@ -4,7 +4,7 @@
 AU_M = 149597870700
 AU_KM = AU_M / 1000.0
 SPEED_OF_LIGHT = 2.99792458e5 * 86400.0 / AU_KM
-OBLIQUITY_ECLIPTIC = 84381.4118 * (1.0 / 3600) * np.pi / 180.0
+OBLIQUITY_ECLIPTIC = 84381.448 * (1.0 / 3600) * np.pi / 180.0
 
 
 def create_ecl_to_eq_rotation_matrix(ecl):

diff --git a/tests/ephemeris/test_orbit_conversion.py b/tests/ephemeris/test_orbit_conversion.py
@@ -0,0 +1,204 @@
+import numpy as np
+
+
+def test_orbit_conversion_relationships():
+    # this uses a very similar idea to the demo notebook - this is a case where we *know* the answer
+    from sorcha.ephemeris.orbit_conversion_utilities import universal_cartesian, universal_keplerian
+
+    # define orbits (no e)
+    q = 10
+    i = 0
+    Omega = 0
+    omega = 0
+    Tp = 0
+    # define constants
+    epochMJD_TDB = 0
+    mu = 1
+    # the answer is: (10,0,0) for all tested orbits. They're at perihelion in a well chosen set of units
+    # this also means the vx = 0, and, since i = 0, vz = 0. vy > 0 is the final constraint from this setup
+
+    for e in [0, 0.1, 0.9999, 1.0, 1.0001, 6.0]:
+        x, y, z, vx, vy, vz = universal_cartesian(mu, q, e, i, Omega, omega, Tp, epochMJD_TDB)
+        assert np.isclose(x, 10.0)
+        assert np.isclose(y, 0.0)
+        assert np.isclose(z, 0.0)
+        assert np.isclose(vx, 0.0)
+        assert vy > 0
+        assert np.isclose(vz, 0.0)
+
+    # we also know that we are invariant under 2 pi rotations in Omega and omega
+    for e in [0, 0.1, 0.9999, 1.0, 1.0001, 6.0]:
+        x, y, z, vx, vy, vz = universal_cartesian(
+            mu, q, e, i, Omega + 2 * np.pi, omega + 2 * np.pi, Tp, epochMJD_TDB
+        )
+        assert np.isclose(x, 10.0)
+        assert np.isclose(y, 0.0)
+        assert np.isclose(z, 0.0)
+        assert np.isclose(vx, 0.0)
+        assert vy > 0
+        assert np.isclose(vz, 0.0)
+        x, y, z, vx, vy, vz = universal_cartesian(
+            mu, q, e, i, Omega - 2 * np.pi, omega - 2 * np.pi, Tp, epochMJD_TDB
+        )
+        assert np.isclose(x, 10.0)
+        assert np.isclose(y, 0.0)
+        assert np.isclose(z, 0.0)
+        assert np.isclose(vx, 0.0)
+        assert vy > 0
+        assert np.isclose(vz, 0.0)
+
+    # finally, if we rotate inclination to 90 deg, we should flip vz and vy
+    for e in [0, 0.1, 0.9999, 1.0, 1.0001, 6.0]:
+        x_0, y_0, z_0, vx_0, vy_0, vz_0 = universal_cartesian(mu, q, e, 0.0, Omega, omega, Tp, epochMJD_TDB)
+        x_90, y_90, z_90, vx_90, vy_90, vz_90 = universal_cartesian(
+            mu, q, e, np.pi / 2, Omega, omega, Tp, epochMJD_TDB
+        )
+        assert np.isclose(x_0, x_90)
+        assert np.isclose(y_0, y_90)
+        assert np.isclose(z_0, z_90)
+        assert np.isclose(vx_0, vx_90)
+        # note these are different now!
+        assert np.isclose(vy_0, vz_90)
+        assert np.isclose(vz_0, vy_90)
+
+
+def test_orbit_conversion_realdata():
+    from sorcha.ephemeris.simulation_parsing import parse_orbit_row
+    from collections import namedtuple
+
+    # constants
+
+    # values from the spice kernel - dec 13 2023
+    gm_sun = 2.9591220828559115e-04
+    gm_total = 2.9630927487993194e-04
+
+    # this is a hack where we are hardcoding the Sun positions at the time (computed using JPL)
+    # note that this needs to be a namedtuple due to the way `parse_orbit_row` expects the input
+    Sun = namedtuple("Sun", "x y z vx vy vz")
+
+    # this is similar to the notebook - values come from JPL and are for asteroid Holman and 2I/Borisov
+    # let's start with Holman
+    epochJD_TDB = 2457545.5
+    # note these are equatorially aligned\
+    sun_epoch = Sun(
+        x=3.743893517879733e-03,
+        y=2.355922092887896e-03,
+        z=8.440770737482685e-04,
+        vx=-7.096646739414067e-07,
+        vy=6.421467712437571e-06,
+        vz=2.788964122162865e-06,
+    )
+    # sun_epoch = Sun(x = 0, y = 0, z = 0, vx = 0, vy = 0, vz = 0)
+    sun_dict = {epochJD_TDB: sun_epoch}
+    # heliocentric keplerian and cometary - note angles are in degrees!
+    e_helio = 1.273098035049758e-01
+    q_helio = 2.719440725596252e00
+    inc_helio = 2.363582123773087e00
+    lan_helio = 1.203869311659506e02
+    aop_helio = 5.506308037812056e01
+    Tp_helio = 2457934.552658705506
+    M_helio = 2.902919054404318e02
+    a_helio = 3.116158215731438e00
+    # heliocentric cartesian (ecliptic)
+    X_helio = -7.569545429706993e-02
+    Y_helio = 3.024083648650882e00
+    Z_helio = -6.044399403284755e-02
+    VX_helio = -9.914117209213893e-03
+    VY_helio = -1.485136186100886e-03
+    VZ_helio = 3.840061650310168e-04
+    # barycentric keplerian and cometary
+    e_bary = 1.277080918842867e-01
+    q_bary = 2.718601009368714e00
+    inc_bary = 2.364051308275402e00
+    lan_bary = 1.203686955102486e02
+    aop_bary = 5.537099088407054e01
+    Tp_bary = 2457936.050825081766
+    M_bary = 2.899920485236385e02
+    a_bary = 3.116618398124679e00
+    # barycentric cartesian (ecliptic!)
+    X_bary = -7.195156074800051e-02
+    Y_bary = 3.026580919478138e00
+    Z_bary = -6.060670045129734e-02
+    VX_bary = -9.914826873812788e-03
+    VY_bary = -1.478135218486216e-03
+    VZ_bary = 3.840106764287660e-04
+
+    # barycentric cartesian (equatorial) - these are the reference values for comparison
+    x_bary_eq = -7.195156074800051e-02
+    y_bary_eq = 2.800941663957977e00
+    z_bary_eq = 1.148299189842545e00
+    vx_bary_eq = -9.914826873812788e-03
+    vy_bary_eq = -1.508913222991139e-03
+    vz_bary_eq = -2.356455160257992e-04
+    vec_bary = np.array([x_bary_eq, y_bary_eq, z_bary_eq, vx_bary_eq, vy_bary_eq, vz_bary_eq])
+    # let's not import pandas - we can use simple dictionaries here
+
+    # COM - note Tp needs to be in MJD for input
+    COM_elements = {
+        "q": q_helio,
+        "e": e_helio,
+        "inc": inc_helio,
+        "node": lan_helio,
+        "argPeri": aop_helio,
+        "t_p_MJD_TDB": Tp_helio - 2400000.5,
+        "FORMAT": "COM",
+    }
+    KEP_elements = {
+        "a": a_helio,
+        "e": e_helio,
+        "inc": inc_helio,
+        "node": lan_helio,
+        "argPeri": aop_helio,
+        "ma": M_helio,
+        "FORMAT": "KEP",
+    }
+    CART_elements = {
+        "x": X_helio,
+        "y": Y_helio,
+        "z": Z_helio,
+        "xdot": VX_helio,
+        "ydot": VY_helio,
+        "zdot": VZ_helio,
+        "FORMAT": "CART",
+    }
+
+    BCOM_elements = {
+        "q": q_bary,
+        "e": e_bary,
+        "inc": inc_bary,
+        "node": lan_bary,
+        "argPeri": aop_bary,
+        "t_p_MJD_TDB": Tp_bary - 2400000.5,
+        "FORMAT": "BCOM",
+    }
+    BKEP_elements = {
+        "a": a_bary,
+        "e": e_bary,
+        "inc": inc_bary,
+        "node": lan_bary,
+        "argPeri": aop_bary,
+        "ma": M_bary,
+        "FORMAT": "BKEP",
+    }
+    BCART_elements = {
+        "x": X_bary,
+        "y": Y_bary,
+        "z": Z_bary,
+        "xdot": VX_bary,
+        "ydot": VY_bary,
+        "zdot": VZ_bary,
+        "FORMAT": "BCART",
+    }
+
+    orbit_types = {
+        "COM": COM_elements,
+        "KEP": KEP_elements,
+        "CART": CART_elements,
+        "BCOM": BCOM_elements,
+        "BKEP": BKEP_elements,
+        "BCART": BCART_elements,
+    }
+    for i in orbit_types:
+        converted = np.array(parse_orbit_row(orbit_types[i], epochJD_TDB, None, sun_dict, gm_sun, gm_total))
+        for j in range(6):
+            assert np.isclose(converted[j], vec_bary[j])