[gdal-dev] Re: [Fwd: Re: Warping an already georeferenced image with control points

[Jan Hartmann]

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?
>>
>> Jan
>>
>> Frank Warmerdam wrote:
>>     
>>> Jan Hartmann wrote:
>>>       
>>>> Hi,
>>>>
>>>> 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.
>>>>         
>
> Hi,
>
> 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
> raster(vrt).
> 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-
>
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>
>   
Hi Jukka,

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.

Jan
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