Converts from custom MarsICRS to MarsFixed using Orekit API

test_frames.py

""" Validate poliastro frames against Orekit ones """

from orekit.pyhelpers import setup_orekit_curdir
from org.hipparchus.geometry.euclidean.threed import Vector3D
from org.orekit.bodies import CelestialBodyFactory
from org.orekit.frames import FramesFactory, Transform, UpdatableFrame
from org.orekit.time import AbsoluteDate
from org.orekit.utils import PVCoordinatesProvider, TimeStampedPVCoordinates

import orekit

# Setup orekit virtual machine and associated data
VM = orekit.initVM()
setup_orekit_curdir("orekit-data.zip")

# Declare the J2000 date and ICRF frame
J2000 = AbsoluteDate.J2000_EPOCH
FRAME_ICRF = FramesFactory.getICRF()

# Get Mars and compute its position w.r.t. ICRF
Mars = CelestialBodyFactory.getMars()
PVMars_ICRF = PVCoordinatesProvider.cast_(Mars).getPVCoordinates(J2000, FRAME_ICRF)

# Compute Mars inertial and fixed frames
MarsINERTIAL = Mars.getInertiallyOrientedFrame()
MarsFIXED = Mars.getBodyOrientedFrame()

# Define MarsICRF as a pure translation of ICRF but centered in current planet
# location
MarsICRF = UpdatableFrame(FRAME_ICRF, Transform(J2000, PVMars_ICRF), "MarsICRF", False)

# Compute the transformation between MarsICRF -> MarsFIXED
MarsICRF_to_MarsFIXED = MarsICRF.getTransformTo(MarsFIXED, J2000)

# Define a PV vector w.r.t. MarsICRF frame
POS = Vector3D(float(7000e3), float(5000e3), float(200e3))  # [m]
VEL = Vector3D(float(0), float(2.5e3), float(0.5e3))  # [m / s]
PV_in_MarsICRF = TimeStampedPVCoordinates(J2000, POS, VEL)

# Apply the conversion from MarsICRF -> MarsFIXED
PV_in_MarsFixed = MarsICRF_to_MarsFIXED.transformPVCoordinates(PV_in_MarsICRF)
computed_pos = list(PV_in_MarsFixed.getPosition().toArray())

# Expected position w.r.t. MarsFIXED (computed with GMAT-2020a)
expected_pos = [-8471.116775897131e3, 845.0749156806216e3, 1251.410786458257e3]
expected_vel = [1.692787736347916e3, -1.145272280803045e3, -0.6168731511636765e3]

# Print computed and expected positions
print(f"{computed_pos = }\n{expected_pos = }")