[Gdal-dev] adding 1 GCP pointless?

[Frank Warmerdam]

Maciek Sieczka wrote:
> I noticed 2 GCPs is the minimum number to be effectively added. What is
> the reason? Is it that less than 2 is not enough for warping the image
> after? But is 2 enough? I though 1st order affine requires at least 3...
> 
> What i was trying to accomplish by adding 1 GCP is the following thing:
> I've lost a worldfile for my tif. But I know the coordinates of one
> characterstic object in the image. I thought I could just add it as
> GCP using gdal_translate and then "move" the whole image to it's
> destination with gdalwarp. Is this impossible?
> 
> Could gdal_translate issue a warning if adding 1 GCP is really
> pointless?

Maciek,

Setting one gcp is pretty pointless, but I checked and gdal_translate was
writing the GCP.  However gdalinfo was not reporting it.  I have fixed
this in CVS.

Best regards,
-- 
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