[Proj] why doesn't the epsg file reference the hpgn grids?

Richard Greenwood richard.greenwood at gmail.com
Tue Mar 17 20:59:26 EST 2015

The epsg file included with proj has definitions for hpgn coordinate
systems that do not use the grid shift files, for example:
# NAD83(HARN) / Wyoming West (ftUS)
<3758> +proj=tmerc +lat_0=40.5 +lon_0=-110.0833333333333 +k=0.9999375
+x_0=800000 +y_0=100000 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=us-ft
+no_defs  <>

So there is no datum transformation applied. But proj has the appropriate
harn grid shift files here:

And changing the above definition to include the grid shift files like
below seems more appropriate:
# NAD83(HARN) / Wyoming West (ftUS)
<3758> +proj=tmerc +lat_0=40.5 +lon_0=-110.0833333333333 +k=0.9999375
+x_0=800000 +y_0=100000 +ellps=GRS80 +nadgrids=wyhpgn.gsb +units=us-ft
+no_defs  <>

Does the proj epsg file get created from data at www.epsg.org? And is that
data lacking the reference to the grid shift files, or is it "lost in
translation"? It seems like there is the wonderful resource in the harn
grids that isn't getting used, but maybe I'm overlooking something.


Richard W. Greenwood, PLS
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