[Proj] gsb file format

[Frank Warmerdam]

Irwin Scollar wrote:
> A question from an outsider:
> 
> The gsb file format appears to have originated with Golden Software 
> for their MapViewer program.  Only two items in the proj4 datum grid 
> list seem to use it.
> 
> Where is it documented? Is it proprietary?

Irwin,

Despite the extension, I think the .gsb files are NTv2 format and are
unrelated to the Golden Software raster format which uses the same
extension.  The NTv2 format was, I believe, initially defined by a
Canadian federal government group though the details escape me just now.
I could likely find more info on this if you really need it though there
have been discussions on the list about NTv2 format doc sources in the not
to distant past.

The lesson: don't trust filename extensions.

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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and watch the world go round - Rush    | Geospatial Programmer for Rent