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I got a problem regarding ephemerides data. The description of the ephemerides data is located here: http://www.navcen.uscg.gov/pubs/gps/sigspec/gpssps1.pdf

I can extract the bits/bytes that are important. I just don't know how to interprete them. It seems there is no information about that. I guess from the document that it should contain Keplerian data to calculate the position of a satellite in "WGS-84 Earth-Centered Earth-Fixed" format, which is what I need.

This document says that I can calculate the final position "utilizing a variation of the equations shown in Table 2-15" The parameters that I need to fill into this terms are Cus Cuc Crc Crs Cic Cis IDOT toe io I know how long these parameters are, but not where to start to read them inside of the datastream

Looking at page 32, I see that they are there, but where they are inside of this block of "words", thats a secret for me.

Can anyone help ?

I dont ask anyone to read the whole pdf, thats a bit too much, but maybe someone has a deep knowledge regarding this topic already.

And this terms are a bit confusing, because some of them are defined recursive

A = sqrt(A^2)
vk = something * Ek
Ek = something * vk

Thanks in advance

Sheradil
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  • did you check this page? (http://www.navipedia.net/index.php/GPS_and_Galileo_Satellite_Coordinates_Computation) have a some hints to understand that file, including the variable vk. – mikesneider Feb 08 '17 at 14:34

1 Answers1

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I'm currently working on similar problems. So far the opensource library gnss-sdr has been of great help. Especially src/core/system_parametes/gps_navigation_message.cc where the function 

int Gps_Navigation_Message::subframe_decoder(char *subframe)

which decodes and stores each subframe is defined.

Ash
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