Swiss Grid Tools

Coordinate transformations involving the Swiss reference frames are not terribly well covered in many standard GIS tools and libraries. I aim at making available some Python code that is supposed to help speed-up people's coordinate transformation tasks.

WGS84-LV03.py

The class Convert provides:

• a method convert (points, typ=['proj4'|'rest']), which converts coordinates from LV03 to WGS84 and vice versa.
  convert detects automatically which direction of conversion is desired.
  points is a list with tuples (easting, northing), or (x,y).
  typindicates whether the REST-service of swisstopo or the local PROJ.4 - library is used.

• The method check_conversion creates an arbitratry number of random coordinates in Switzerland, both in LV03 and WGS84, and converts them using both, the REST-service and the local projection librtary. The differences (which seem to be always on the order of 1 cm) are returned.

The "shiftgrid" file chenyx06etrs.gsbis essential for a good transformation. It is contained in this repo, but you might want to rename it. This is because if the file is not found, the latest one will be downloaded from the swisstopo site. But beware: There is no guarantee that the respective URL will remain valid.

Example

from WGS84-LV03 import Convert

bern = (7.43861, 46.951)
zurich = (8.55, 47.37)
C = Convert()
C.convert([bern, zurich])

Out[1]: 
[(599998.2101365564, 199990.7321469287),
 (683940.6285646699, 247167.5578803884)]

TODO

• Deal with the "new" LV95.

References

• swisstopo REST-service
• swisstopo LV03 documentation
• swisstopo LV95 documentation
• The PROJ.4 library
• "pyproj", the Python intrface to PROJ.4