-- AlfredoQuesada - 10 Feb 2009

Hello

I've just arrived to this world of GPS data, and I'm trying to add A-GPS support to a GPS module. According to module's datasheet aiding data must be sent in the frame format specified by IS-GPS-200, allowing the use of frames 1 to 3 for ephemeris, and 4 to 5 for almanac IIRC.

After looking at IGS website I've seen you can get some of this data in both rinex and sp3 file formats, which seem to be representing different things. If I'm not wrong the data needed to fill frames 1 to 3 can be extracted from rinex files, and the problem here is how to format them in order to get an IS-GPS-200 compatible byte stream. Data in rinex files seems to contain all required fields, but I don't think you can send them to the module without a previous preprocessing.

On the other side we have the sp3 format. If you want to use predicted data in the future (makes sense to me, because data from previous days should be meaningless) I believe this is the format that you need. The problem here is that probably this satellite location should be converted somehow to make it compatible with frames' format. Maybe the topic called "ConversionSP3toRinexNav" is related to this problem.

So.. what do you think? (maybe I'm misunderstanding something.. I'm really newbie with GPS)

Thx in advance and regards
Topic revision: r1 - 10 Feb 2009, AlfredoQuesada
 

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