[gdal-dev] Re: [Fwd: Re: Warping an already georeferenced image
with control points
j.l.h.hartmann at uva.nl
Mon Feb 9 05:15:22 EST 2009
Jukka Rahkonen wrote:
> Jan Hartmann <j.l.h.hartmann <at> uva.nl> writes:
>> No, this doesn't seem to work. Although the coordinate system *is*
>> retained when I add -a_srs to the gcps, the boundaries of the input file
>> are discarded: they are reset to the pixel dimensions of the file. Is
>> this a bug?
>> Frank Warmerdam wrote:
>>> Jan Hartmann wrote:
>>>> I am trying to georeference old maps in two steps: first
>>>> georeferencing them from the old projection to a modern one, and then
>>>> ameliorating the georeferenced image by rubber-sheeting it on the
>>>> base of control points, mostly triangulation points for which the
>>>> coordinates in the old and new maps are known.
>>>> The second step causes trouble: if I add control points to the
>>>> georeferenced image with gdal_translate -gcp , the projection
>>>> information gets lost.
> I am not sure if I understood how you trying to do the job, but hopefully my
> task and work flow are close enough to be useful for you.
> 1. Let's say that the original image is in epsg:2393 and target is epsg:3067.
> 2. I insert some ground control points in epsg:3067 with gdal_translate and
> -gcp. Image format of the temporal output file can be GeoTIFF but also virtual
> 3. I warp the temporary image, now containing gpc's in epsg:3067 projection, to
> final product using gdalwarp as
> gdalwarp -s_srs epsg:3067 -t_srs epsg:3067.
> -Jukka Rahkonen-
> gdal-dev mailing list
> gdal-dev at lists.osgeo.org
You have described exactly what I want to do, but the problem is that in
step 2, inserting gcps, the georeferenced boundaries of the file are
lost. Eventually you get a somewhat displaced raw raster file.
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