HarnGrids

With the support of i-cubed, I (Frank Warmerdam) have written tools to translate the HPGN grids from NOAA/NGS from .los/.las format into NTv2 format for convenient use with PROJ.4. This project included implementing a .los/.las reader for GDAL, and an NTv2 reader/writer. Also, a script to do the bulk translation was implemented in https://github.com/OSGeo/gdal/tree/trunk/gdal/swig/python/samples/loslas2ntv2.py. The command to do the translation was:

  loslas2ntv2.py -auto *hpgn.los

As GDAL uses NAD83/WGS84 as a pivot datum, the sense of the HPGN datum shift offsets were negated to map from HPGN to NAD83 instead of the other way. The files can be used with PROJ.4 like this:

  cs2cs +proj=latlong +datum=NAD83 
        +to +proj=latlong +nadgrids=./azhpgn.gsb +ellps=GRS80

# input:
-112 34

# output:
111d59'59.996"W 34d0'0.006"N -0.000

This was confirmed against the NGS HPGN calculator.

The grids are available at http://download.osgeo.org/proj/hpgn_ntv2.zip

Use at your own risk!

See Also: HTDPGrids