NonFreeGrids

Not all grid shift files have licencing that allows them to be freely distributed, but can be obtained by users through free and legal 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: http://www.geod.nrcan.gc.ca/tools-outils/ntv2_e.php.

Procedure:

1. Visit the NTv2, and register/login
2. Follow the Download NTv2 link near the bottom of the page.
3. 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

1. Test it using:

cs2cs +proj=latlong +ellps=clrk66 +nadgrids=@ntv2_0.gsb +to +proj=latlong +ellps=GRS80 +datum=NAD83
-111 50
111d0'3.006"W   50d0'0.103"N 0.000  # correct answer