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SGL-UT / gnsstk

The goal of the gnsstk project is to provide an open source library to the satellite navigation community--to free researchers to focus on research, not lower level coding.
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RINEX v3 doesn't correctly handle invalid xmitTime #23

Open peci1 opened 5 months ago

peci1 commented 5 months ago

https://github.com/SGL-UT/gnsstk/blob/cbba16f6d2738c3ee2445fc913ba7d346f7e1fed/core/lib/FileHandling/RINEX3/Rinex3NavData.cpp#L1017

According to the standard, if the xmitTime is set to .9999+e09, then it should be treated as invalid/unknown. However, the library doesn't do this and uses this value as if it were proper.

The following call to fixTimeGPS() then destroys navOut.xmitTime by adding this invalid value to a GPS week nr.:

https://github.com/SGL-UT/gnsstk/blob/cbba16f6d2738c3ee2445fc913ba7d346f7e1fed/core/lib/NewNav/RinexNavDataFactory.cpp#L344

Apparently, this one place where the invalid value destroys things could get easily fixed by treating the invalid value as 0, but I'm not sure whether there are other places where it could make problems.

One of the problematic RINEX v3 files is e.g. this one: https://igs.bkg.bund.de/root_ftp/MGEX/BRDC/2024/001/BRDC00WRD_S_20240010000_01D_MN.rnx.gz . E.g. the very first nav message:

E08 2023 12 31 23 50 00-2.009316231124e-04-5.940137270954e-12 0.000000000000e+00
     1.500000000000e+01-1.201562500000e+02 2.852261665290e-09-3.006433072931e+00
    -5.470588803291e-06 1.602121628821e-04 8.979812264442e-06 5.440613040924e+03
     8.580000000000e+04-8.195638656616e-08 4.684350206789e-01-9.313225746155e-09
     9.662984159677e-01 1.517812500000e+02 7.945787833385e-01-5.399510625576e-09
    -2.142946405177e-12 5.170000000000e+02 2.295000000000e+03 0.000000000000e+00
     3.120000000000e+00 0.000000000000e+00-3.725290298462e-09-4.423782229424e-09
     9.999000000000e+08

You can see the 9.999000000000e+08 in the very last position. This is what makes problems.

Reproducer:

gnsstk::NavLibrary lib;
gnsstk::NavDataFactoryPtr fac = std::make_shared<gnsstk::RinexNavDataFactory>();
fac->addDataSource("BRDC00WRD_S_20240010000_01D_MN.rnx");
lib.addFactory(fac);
std::cout << gnsstk::printTime(gnsstk::CivilTime(lib.getInitialTime()), "%Y-%m-%d %H:%M:%f") << " --- "
          << gnsstk::printTime(gnsstk::CivilTime(lib.getFinalTime()), "%Y-%m-%d %H:%M:%f") << std::endl;

Initial time is wrongly in year 2055 and final time is also weird:

2055-8-30 22:0:0.000000 --- 2023-12-25 4:0:0.000000