Proposal: Add use option also for three character observation type

Dear Scivision,

I can confirm that your effort to speed up the parsing, by making the indicators optional, was successful.

Unfortunately, the parsing is still a bit slow. I have another proposal to speed it up:

The use argument is very useful to speed up the parsing, by selecting only the constellations/satellites you want. Especially ignoring the GEOs makes a big different, since they are recorded every single epoch. How do you feel about adding an option to allow a similar selection for the signal types?

Here is an example of what I would like to do:

#Only read Galileo E1 Code
gr.readrinex('test.rnx', use='E', signal='C1C')

#Read all code and phase observations of all constellations but GEOs
gr.readrinex('test.rnx', use=['E', 'G', 'C', 'R', 'J'], signal=['C', 'L'] )

I am convinced the potential time saving is substantial.

Implementing this, one may consider changing the use keyword, since it is not unambiguous anymore. But this is a detail.

Thanks a lot for your effort. Keep up the good work!

Best Regards Volker

[scivision]

Thanks Volker, yes due to read buffering and the like, it is very speedy to just skip satellites. Right, for the command-line ReadRinex as well as the direct Python API, a new keyword is needed to include specific measurements. Yes I think this will at least offer substantial memory benefits, as often we use only a few of the ~30 measurements available for each satellite

[VOMAY]

I just tested it for OBS3 and it works like a charm. Thanks a lot! This will save me a lot of time.