[Geotiff] Proposed TOWGS84 GeoKey for GeoTIFF

[Christian Zietz]

Frank Warmerdam schrieb:

> It has been an irritant to me for some time that there is no way of
> recording a preferred datum transformation for a coordinate system in
> GeoTIFF format.  I would like to rectify that with an unofficial GeoKey
> to record OGC WKT style TOWGS84 values.  I have written up a brief
> proposal at:
> 
>    http://trac.osgeo.org/geotiff/wiki/TOWGS84GeoKey

Let me add that the test file I prepared while proposing this feature
still exists at <http://www.chzsoft.de/geo/GeogToWGS84GeoKey5.zip>.

>From what I see, your proposal is functionally identical to the one we
agreed upon in 2008 [1], so I hope the existance of this test file will
help while implementing the GeogTOWGS84GeoKey. Maybe the "Cookbook for
expressing a user defined datum" and the "Note for libgeotiff users"
written back then would make a good addition to the documentation of
this new key.

Glad to see this is coming along.

Christian

[1]
<http://osgeo-org.1803224.n2.nabble.com/User-defined-datum-Transformation-parameters-td2065066.html>
-- 
Christian Zietz  -  CHZ-Soft  -  czietz at gmx.net
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