Proposed TOWGS84 GeoKey for GeoTIFF

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Proposed TOWGS84 GeoKey for GeoTIFF

Frank Warmerdam
Folks,

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

I am interested in thoughts from the community.  Barring suggested
improvements or strong negative feedback I'll commit that in libgeotiff
trunk shortly.

Best regards,
--
---------------------------------------+--------------------------------------
I set the clouds in motion - turn up   | Frank Warmerdam, [hidden email]
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent

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Re: 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>
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Christian Zietz  -  CHZ-Soft  -  [hidden email]
WWW: http://www.chzsoft.de/
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Re: Proposed TOWGS84 GeoKey for GeoTIFF

Frank Warmerdam
On 11-03-07 04:39 PM, Christian Zietz wrote:

> 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,

Well, I'm quite embarrassed to have forgotten our past discussion.  I'm
encouraged that our solutions were identical indicating in some ways it
is the obvious solution.  I have incorporated some of your test into the
page at:

   http://trac.osgeo.org/geotiff/wiki/TOWGS84GeoKey

and added your sample file on the samples download directory.  I'm sorry
for having lost track of our previous discussion.  I think it is because
things switched track into PixelIsPoint discussions. :-)

Since there has been no negative feedback now or during the original
discussion, I am going to go ahead with adding this to libgeotiff as
an unofficial extension of the spec.

Best regards,
--
---------------------------------------+--------------------------------------
I set the clouds in motion - turn up   | Frank Warmerdam, [hidden email]
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent

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