Processing NAV file without GLONASS cause error

[plutonheaven]

Function convert_nav_dataset_to_dataframe of src/prx/rinex_nav/evaluate.py assumes that GLONASS is present in RNX NAV file.

When it is not the case, the following line causes an error:

df["frequency_slot"] = df.FreqNum.where(df.sv.str[0] == "R", 1).astype(int)

due to the absence of FreqNum in the parsed NAV file.

This happened when I tried to process TLSE00FRA_R_20220010000_01D_30S_MO.rnx.gz. The file BRDC00WRD_R_20213650000_01D_MN.rnx was downloaded and produced an error.

[plutonheaven]

When downloading BRDC00IGS_R_20213650000_01D_MN.rnx, the issue does not appear.

[plutonheaven]

I also noticed that WRD NAV files don't have iono corrections, linking this issue to #52 (for missing iono) and to #189 (for missing constellations).

[plutonheaven]

I advise to use the FTP server gssc.esa.int, which has BRDC00IGS_R_ from 2016-01-01 (not fully checked). For older data, we would have to investigate more...