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

[Jan Hartmann]

Thanks Jukka, that is an interesting article in its own right, and it is 
relevant to historical maps too. Your solution is viable, but it takes 
more work (insert corner gcp in each image), which shouldn't be 
necessary, as this information is already available but is discarded by 
gdal_translate. If gdal_translate could keep this information in the 
target file, even when gcps have been added, everything would be fine 
(and my impression is it should).

Jan

Rahkonen Jukka wrote:
> Jan Hartmann <j.l.h.hartmann <at> uva.nl> writes:
>  
> Jukka Rahkonen wrote:
>  
> >> 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.
> >
> >
> >> 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
>  
> Hi,
>  
> That displacement could be avoided at least by inserting manually gcp 
> to each
> corner of the image. Perhaps this article gives some ideas:
> http://www.scangis.org/scangis2007/papers/r3_rahkonen.pdf
>  
> -Jukka-
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