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osqzss / gps-sdr-sim

Software-Defined GPS Signal Simulator
MIT License
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$GPRMC "Speed over ground" inconsistent #278

Open Tom-sp765 opened 3 years ago

Tom-sp765 commented 3 years ago

When I transmit a gpssim.bin file built with this software, the "speed over ground" in the $GPRMC messages output by the receiver I am using to record the transmission is always inconsistent (much slower than, and seemingly uncorrelated) with the simulated movement.

Everything else works beautifully. Is this something I can fix by changing a parameter?

osqzss commented 3 years ago

The unit of the speed over ground in the RMC message is knot.

Tom-sp765 commented 3 years ago

Thanks for replying - if I simulate a journey in which mean speed calculated from the location and time data is 50 knots, I'm getting a mean "speed over ground" of between 0 and 3 knots, and apparently no correlation between the speed over ground and the simulated speed. It's not just less - it doesn't appear to be related.

I've noticed a similar issue with "course over ground" - it doesn't seem to relate to the simulated direction inferred from the location coordinates, in the same way it does for "real" data.