Is there a parser for Earth Explorer File (EOF)?

Orekit usage
1

Hi, like in the title, is there a parser for a file like this:
S3A_SR___ROE_AX_20230822T190118_20230822T204318_20230822T210013___________________POD_O_NR____.EOF (298.8 KB)
And if not is there a way to create bounded propagator (like from SP3 ephemeris) based on ephemeris this file contains?

2

There are no parsers for this yet, but it does not seem really difficult to add, and to have the parser generate a bounded propagator from this.
Do you have a publicly available specification for the format?
You can also contribute such a parser, of course :wink:

3

Hey, I’m afraid I’m not versed enough in java to contribute yet but I’ll think about it ;). In the meantime I’ve managed to write a “parser” in python. I’ve got pandas dataframe with my data (datetime, X, Y, Z, VX, VY, VZ), I can easily convert it to java’s list of absolutePVCoordinates or SpacecraftStates, but I’m not sure what next. Most of the time I work with SP3 files so I would like to have ephemeris that works similarly. Would copying SP3Ephemeris class work, but instead SP3Coordinates I would have my own coordinates class?

4

Hi @jlipinski,

Once you have the list of SpacecraftStates you can instantiate an Ephemeris object which implements the BoundedPropagator interface.

Is that what you’re looking for?

5

Yes, kinda.

First there is a problem that EOF gives coordinates in ITRF so I need to change frame to EME for example, otherwise I get this error:

Java stacktrace:
org.orekit.errors.OrekitException: non pseudo-inertial frame "CIO/2010-based ITRF simple EOP"
	at org.orekit.attitudes.LofOffset.(LofOffset.java:110)
	at org.orekit.attitudes.LofOffset.(LofOffset.java:66)
	at org.orekit.propagation.SpacecraftState.(SpacecraftState.java:305)

So I have my DataFrame eof_df in which I have AbsolutePVCoordinates in ITRF frame, I change them to EME2000 and I build list of spacecraft states:

eme = FramesFactory.getEME2000()
states = ArrayList().of_(SpacecraftState)
for i in eof_df["AbsPV"]:
    timestamped = i.getPVCoordinates(eme)
    state = SpacecraftState(AbsolutePVCoordinates(eme, timestamped.getDate(), timestamped.getPosition(), timestamped.getVelocity()))

Next I’ve tried to instantiate Ephemeris and use it like I would use BoundedPropagator:

eph = Ephemeris(states, len(eof_df))
eph.getPVCoordinates(AbsoluteDate(2023,8,22,18,22,45.,TimeScalesFactory.getUTC()), itrf)

but for dates that are not in the original file it results in NaN, for example:
2023-08-22 18:22:44 (this date is in original file):

<TimeStampedPVCoordinates: {2023-08-22T18:22:44.000, P(2502431.1836890006, 1811624.8780950003, 6474349.140417), V(-3455.508078, -5984.095810000002, 3003.599313000001), A(-0.8594268176616594, 0.5135932201750665, 2.1896576856306276E-6)}>

2023-08-22 18:22:45 (this date is NOT in original file):

<TimeStampedPVCoordinates: {2023-08-22T18:22:45.000, P(NaN, NaN, NaN), V(NaN, NaN, NaN), A(NaN, NaN, NaN)}>

Is there something about constructing and propagating ephemeris that I don’t understand?

6

Hi again,

I think you should reduce the number of interpolation points.
Change this:
eph = Ephemeris(states, len(eof_df))
With this:
eph = Ephemeris(states, 8)
I’ve chosen 8 because it’s a typical value. SP3Parser in Orekit uses 7 so you could also choose that number.

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