Question

I would like to generate the raw navigation subframes from RINEX files. I have code that reads in a current RINEX file but would like to build subframes 1, 2 and 3 as if they had just been received from the satellite. Is this possible? And if so, does the GPStk have tools to do this?

Thanks in advance! -ja

-- JonAxelson - 04 Feb 2008

Answer

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Well the answer is it depends on the fidelity of what you are trying to reassemble. It is not possible to exactly obtain the bit pattern that was transmitted from the satellite because the raw data actually has more information in it than the RINEX file. However, could you reconstruct something that is in the same format, could be interpreted to get the same RINEX data back out of it? The answer is yes.

There is code in the GPSTk that goes from raw format to engineering units (like that in a RINEX file) but not the other direction. Basically you will need to convert from the engineering units to the raw scaled integers, put the integers in the correct ordering and recompute the parity. If you want to look at some of the GPSTk code that goes from raw->engineering units you can find it in the references below. Also you could use the GPSTk functionality to verify you implemented this correctly. Finally if you have a working implementation, please consider contributing it to the GPSTk.

EngEphemeris:addSubframe()

EngNav::subframeConvert()

EngNav::subframeParity()

-- RickMach - 05 Feb 2008