PyGNSS - Analysis and visualization of precise GNSS orbits

Functions for downloading, time conversion, reprojection and visualization of precise GNSS orbits. GPS satellites are supported currently, Galileo and Baidu are planned.

First we have to import the package.

import PyGNSS as pyg

We are using standard libraries, like pandas, datetime, numpy, io, ftplib, subprocess, and os. In addition pyproj is required for reprojection.

Than we download current satellite precise orbit data from FTP.

orbit_fn = pyg.download_sp3() # Current time
orbit_fn = pyg.download_sp3(datetime, data_folder) # Specify time and location

The SP3 file has to be read and parsed to pandas DataFrame.

sp3_df = pyg.read_sp3(orbit_fn)

We get a DataFrame similar to this.

vehicle,date_time,coor_x,coor_y,coor_z,clock,std_x,std_y,std_z,std_c
G01,2017-02-16 05:59:42,20817.041254,11237.897309,12227.333238,49.358711,7,9,7.0,209
G02,2017-02-16 05:59:42,-12699.223656,-22142.330686,8454.724099,474.920193,4,9,8.0,218
G03,2017-02-16 05:59:42,15161.772458000001,2522.990136,21654.710355000003,-107.445348,8,11,6.0,218
G05,2017-02-16 05:59:42,-4801.552475,-21052.092561,-15417.360146,-60.386646999999996,11,6,7.0,209

Next we convert ECEF coordinates to longitude, latitude and altitude. Original coordinates can be deleted or left in the DataFrame. In addition we can consider Greenwich Mean Sidereal Time.

sp3_df_lla = pyg.convert_ecef2lla(sp3_df, True, True) # Remove original coordinates, consider GMST
sp3_df_lla = pyg.convert_ecef2lla(sp3_df) # Do not remove original coordinates, do not consider GMST, default

The satellite orbit DataFrame looks like this after conversion.

vehicle,date_time,clock,std_x,std_y,std_z,std_c,lat,long,alt
G01,2017-02-16 05:59:42,49.358711,7,9,7.0,209,27.370416376559717,-6327.494098728924,20256.18947880152
G02,2017-02-16 05:59:42,474.920193,4,9,8.0,218,18.353417008491363,-6475.691535287722,20513.295509668373
G03,2017-02-16 05:59:42,-107.445348,8,11,6.0,218,54.676874210567846,-6346.408384352559,20191.144848877248
G05,2017-02-16 05:59:42,-60.386646999999996,11,6,7.0,209,-35.57079350017397,-6458.704318969671,20160.960582937056

This DataFrame can be written to KML and later visualized in Google Earth. Orbits are displayed as lines for each of the GPS satellites. In addition for every satellite we have positions in time. Google Earth time feature enables time navigation.

kml_fn = orbit_fn.split(".")[0]+".kml"
pyg.write_kml(sp3_df_lla, kml_fn)

Krištof Oštir and Polona Pavlovčič Prešeren
University of Ljubljana, Faculty of Civil and Geodetic Engineering
(c) 2017