[gdal-dev] Warping onto an image with only GCPs

[Knut-Frode Dagestad]

Hi,

Hróbjartur Þorsteinsson explained to me a near-hidden feature of GDAL, 
namely to reproject one image onto the coverage of another.

Given two images:
imageA.tiff
imageB.tiff

Then an empty image can be created from image A with e.g.
$ gdal_translate -ot Float32 -scale 0 0 999 999 -a_nodata 999 
imageA.tiff domainA.tiff

And then imageB can be warped onto the extent of this image simply with:
$ gdalwarp imageB.tiff domainA.tiff

domainA.tiff will then contain the data from imageB, exactly co-located 
with imageA.

The problem is that this only works when imageA contains a geotransform, 
and not when it contains only GCPs.


So my question is:
Is there any workaround to warp data from one image onto another image 
which is geolocated by GCPs only?



With the -to option of gdalwarp it is possible to pass some parameters 
to GDALCreateGenImgProjTransformer2(). In the documentation of this 
function I find the following option:

"METHOD: may have a value which is one of GEOTRANSFORM, GCP_POLYNOMIAL, 
GCP_TPS, GEOLOC_ARRAY, RPC to force only one geolocation method to be 
considered on the source dataset."
http://www.gdal.org/gdal__alg_8h.html#94cd172f78dbc41d6f407d662914f2e3

But there is no corresponding option to force use of GCP_POLYNOMIAL for 
the *destination* dataset. I guess this is a bad sign?


Thank you for any help!
Knut-Frode