[Gdal-dev] GCPs to geo transform

[Antoine Hue]

Le 23 févr. 06, à 22:16, Frank Warmerdam a écrit :

> Antoine Hue wrote:
>> Hello,
>> I was wondering if it is possible to compute the geo transform given 
>> a set of GCPs without warping the image?
>> That's what is being done in the osgTerrain  library I am using, it 
>> is warping the image to a geotiff as soon as there are GCPs without 
>> checking if the source and destination CS are the same.
>> Thanks a lot for the GDAL, it is doing a lot for me.
>
> Antoine,
>
> Perhaps the GDALGCPsToGeoTransform() function would be of some use to 
> you.
> It computes an approximate geotransform from a set of GCPs.
>
>
Hello Frank,

Thanks for the answer. That is what I am looking for, I will try it as 
soon as possible .
What do you mean by approximate? Is it less precise than a warp?
Would a warp get better result because of the resampling and filters?

Talking warp, when an image is warped with CS transformation, it is 
likely to be rotated and non rectangular anymore.
Is there a way to access only the data bearing pixels of the warped 
image?
In fact, if several warped images are shown together without caring 
about the no data part of the image, a black portion will appear and 
overlap with actual data.

Thanks,

Antoine