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Old 05-09-2019, 01:31 PM   #1
rnturn
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GPS ephemerides data


Probably an off-the-wall question for most LQ readers...

I ran across some (really) old code that I'd written that decodes the GPS satellite ephemerides from the 50bps data stream that rides on the received GPS satellite signals. My old code took (and could take again) the hexadecimal representation of that data stream and creates the needed parameters for the Kepler equations that give SV position. I thought it might be fun to convert that old PDP-11 FORTRAN-IV code to C or Python as a interesting weekend project for when rain keeps the bike on the rack.

Anyway, I'm looking for a freely-available source of that GPS data stream. Has anyone run across a freely available source for this kind of data? I keep running across subscription services for the ephemerides--which all seem to be tied to a commercial product that needs the data--but I'd rather trust the old code as it was validated as producing correct results when it was written. (Plus... I'm a cheapskate.) Back in the day, the education organization I worked for would gladly supply this data (obtained from a GPS receiver we had hanging off one of the computers in our lab) to anyone who asked---as a "just send us a floppy" sort of deal. I'd contact the current denizens of my old lab but I suspect that a.) most of them have moved on and, more importantly, b.) that GPS receiver has almost certainly been taken out of service---years ago.

Anyone got any leads they can pass along while I continue my searching?

Cheers...
 
Old 05-09-2019, 03:26 PM   #2
michaelk
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Hopefully this is what you are looking for.

https://cddis.nasa.gov/Data_and_Deri...eris_data.html

It probably is off the wall for most members...
 
Old 05-10-2019, 11:02 AM   #3
rnturn
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Quote:
Originally Posted by michaelk View Post
Hopefully this is what you are looking for.

https://cddis.nasa.gov/Data_and_Deri...eris_data.html

It probably is off the wall for most members...
Interesting stuff on that site (shame the background graphic makes it so hard to read) but it seems to be geared toward those interested in studying plate tectonics. I'm looking for the 50bps data stream coming from the GPS SVs themselves. I'd post an example but I'm in the middle of trying to rebuild the system that has the floppy drives I'd need to pull an example from an old diskette. I could use one of those examples for my testing but those old data files are from before the GPS constellation was even complete so they're not useful---except for testing. Bummer that the hardware failure is keeping those locked away for now. Hence my search... :^(
 
  


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