Hi,
Today I tried the TLEBasedOrbitDetermination, and finally figured out that it is wrong, which is corresponding to the frame.
The measurement Position don’t have a property referenceFrame like AngularRaDec, for commonly using, EME2000 is the default frame.
But for TLEBased, TEME is the default frame, mainly for TLEPropagator.
So in theoreticalEvaluation of Position, the frame of states[0] is TEME, and so the frame of pv and pv.getPosition() both are TEME.
Though, in readSp3 of AbstractOrbitDetermination, transformation is done, but the initialGuess.getFrame() is EME2000.
That is, the observed is in the frame of EME2000, but the estimatedValue is in the frame of TEME.
// Measurements
final List<ObservedMeasurement<?>> measurements = new ArrayList<>();
for (final SP3Coordinate coordinates : ephemeris.getCoordinates()) {
final AbsoluteDate date = coordinates.getDate();
final PVCoordinates pvInertial = ephFrame.getTransformTo(initialGuess.getFrame(), date).transformPVCoordinates(coordinates);
measurements.add(new Position(date, pvInertial.getPosition(), 1, 1, satellite));
}
And in compareWithReference of TLEBasedOrbitDetermination, the reference position and velocity should be in the frame of EME2000, but the estimatedOrbit is in the frame of TEME, so as the estimatedOrbit.getPVCoordinates().
The patch is as followings (two modifications):
final PVCoordinates pvInertial = ephFrame.getTransformTo(initialGuess.getFrame(), date).transformPVCoordinates(coordinates);
==>
final PVCoordinates pvInertial = ephFrame.getTransformTo(FramesFactory.getTEME(), date).transformPVCoordinates(coordinates);
System.out.println("ΔP_final(m) = " + Vector3D.distance(refPos, estimatedOrbit.getPVCoordinates().getPosition()));
==>
System.out.println("ΔP_final(m) = " + Vector3D.distance(refPos, estimatedOrbit.getPVCoordinates(frame).getPosition()));
The correct output is as followings:
Input TLE:
1 32711U 08012A 16044.40566026 -.00000039 00000-0 00000+0 0 9991
2 32711 55.4362 301.3402 0091577 207.7302 151.8353 2.00563580 58013
iteration evaluations ΔP(m) ΔV(m/s) RMS nb Range nb Range-rate nb Angular nb PV Px Py Pz Vx Vy Vz
0 1 511.003584235565 0/0 0/0 0/0 0/0 13931962.174999300 -22865909.044731975 -6.225455448 1869.429512489 1120.737098643 3164.781379062
1 2 911.048401 0.128906076 75.485468591314 0/0 0/0 0/0 0/0 13931521.729121314 -22866248.004540220 -728.113858094 1869.510166847 1120.639098994 3164.758846421
2 3 0.013712 0.000002413 75.485183664449 0/0 0/0 0/0 0/0 13931521.722691838 -22866247.992519250 -728.112385653 1869.510165477 1120.639098733 3164.758844451
Estimated TLE:
1 32711U 08012A 16044.40566026 -.00000039 00000-0 00000-0 0 9992
2 32711 55.4358 301.3401 0091588 207.7163 151.8474 2.00563453 58017
Comparison with reference orbit from SP3 file
=============================================
Initial TLE from external provider:
date:2016-02-13T09:44:09.046464Z
frame:EME2000
ΔP_init(m) = 914.4273995963578
ΔV_init(m/s) = 0.1286721455911397
Estimated:
ΔP_final(m) = 59.62588130279602
ΔV_final(m/s) = 0.013449782312139313
Estimated orbit: Cartesian parameters: {P(1.3931521722670417E7, -2.2866247992540702E7, -728.112432160086), V(1869.510165478349, 1120.6390987299053, 3164.7588444503526)}
Estimated orbital parameters changes:
1 Px -440.452307462692 (final value: 13931521.722691838000)
2 Py -338.947787273675 (final value: -22866247.992519250000)
3 Pz -721.886930204866 (final value: -728.112385652757)
4 Vx +0.080652987658 (final value: 1869.510165477021)
5 Vy -0.097999909381 (final value: 1120.639098733136)
6 Vz -0.022534610578 (final value: 3164.758844451251)
Estimated propagation parameters changes:
Estimated measurements parameters changes:
Number of iterations: 2
Number of evaluations: 3
wall clock run time (s): 1.415