Non-Free Grids
Not all grid shift files have licencing that allows them to be freely distributed, but can be obtained by users through free and legal C downloading methods.
Canada NTv2.0
Although NTv1 grid shifts are provided freely with PROJ.4, the higher-quality NTv2.0 file needs to be downloaded from Natural Resources Canada. More info here.
Procedure:
- Register or log-in to the Canadian Spatial Reference System Online Database
- Click "Go" to the "GSD Software", and download "NTv2.0" (approx. 8.3 MB)
- Unzip "ntv2_100325.zip" (or similar), and move the grid shift file "NTV2_0.GSB" to the proj directory--be sure to change the name to lowercase for consistency
- e.g.: mv NTV2_0.GSB /usr/local/share/proj/ntv2_0.gsb
- Test it using: cs2cs +proj=latlong +ellps=clrk66 +nadgrids=@ntv2_0.gsb +to +proj=latlong +ellps=GRS80 +datum=NAD83
then type -111 50- Correct answer should be: 111d0'3.006"W 50d0'0.103"N 0.000
