[Proj] Dutch correction grid

[Frank Warmerdam]

On 11-04-08 12:54 PM, Jan Hartmann wrote:
> I see. So this would be a floating point grid with two bands, the first for the
> x (lon) offset, the second for the y (lat) offset. All measurements in arcseconds.
>
> It's not meant for a datum shift, I've got two targets:
>
> - maps in epgs:28992 (Dutch coordinates, with corrections on a regular grid up
> to 25 cm)
>
> - maps in the 19th century Bonne-based projection, with corrections for about
> 1000 triangulation points (mostly church towers), up to 60 meters. These should
> have to be gridded.
>
> Am I correct that I can create NTv2 files this way and use them in the
> PROJ-parameter list as @nadgrids=...NTV2?

Jan,

Ah, I had not paid close enough attention to realize the above.  I think
it can still work if you convert the shifts into arcseconds.  Note that
the shifts will be applied in PROJ.4 by converting to lat/long, applying
the shift, and shifting back.  There may be some subtleties to how you
setup your coordinate system definitions to trigger proper use of the
NTv2 file.

Best regards,
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