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

[Jukka Rahkonen]

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-