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I'm new to this site so I want to apologize beforehand for all the mistakes I could make while writing this.

So just to put my situation into context : I am currently an intern in an AI company tasked with understanding "classical" RINEX files post-processing algorithms so that I could implement new ones that will use a neural filter instead of more "classical" ones such as Kalman, EKF, etc.

To be completely honest, I am fairly new to GNSS in general and these last months have been particularly frustrating for me since I can't seem to find decent documentation about some aspects of the post-processing I mentioned since I guess most people who work in this field don't bother understanding the algorithms behind RTKPOST for instance, and much less bother understanding the theory behind them thus don't bother documenting the latter in detail, and so what I'm going to ask might be very trivial for most of you reading this and I'm sorry if that's the case. Anyway :

There's this dataset I wanted to post-process manually (https://github.com/IPNL-POLYU/UrbanNavDataset, the Tokyo/Shinjuku one I used base_trimble.obs for observation data and base.nav for navigation data) using the Satellite Coordinates Computation Method described there https://www.johnsonmitchelld.com/2021/03/14/least-squares-gps.html for getting the satellites coordinates from corresponding ephemeris data, and then apply a basic Unweighted Least Squares Method without considering more technical errors (such as ionospheric and tropospheric delays etc) just to get a proof of concept. But I came across a few problems while doing so :

  • How are observation and navigation data supposed to match and why is there observation data only within the 6th hour ? The observation data is only recorded during the 6th hour while the navigation data is recorded. Maybe it's just me using the wrong files and if that's the case please inform me about how I am supposed to get the matching files. And that leads to my next question :

  • How to reconstruct the missing data from the navigation files ? I've tried to find documentation about some sort of model that could interpolate them using Kepler's Laws or more advanced orbital mechanics but none of what I've found seems to introduce an actual algorithm to do that so I'm a bit lost at this point (Sure, I have found techniques such as polynomial interpolation, matrix completion and others but I'd like to find a more widely used one if there's such a thing)

  • Actually, more generally I'd like to find decent documentation about how the RTKPOST app from RTKLIB actually works since I want to figure out the post-processing it does in the background and so far all the documentation I've found is only about how to use it

As trivial to some people here as those problems might be, any help just regarding the two questions I asked above would be hugely appreciated.

I'm looking forward to your answers

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