[gdal-dev] Re: Add GCP's to a file

[Frank Warmerdam]

Jukka Rahkonen wrote:
> Frank wrote:
> 
>>> Also the extents reported by gdalinfo are the widest possible extents
>  and if 
>>> those are to be used only UL coordinated can be used as it.  For 
> other three
>>> corners there is a need to minus one pixel size in one or both axis 
> directions.
> 
>> The lower right corner reported by gdalinfo would be at
>> pixel/line coordinate (xsize,ysize).
> 
> Last pixel/line of, let's say 1000 by 1000 pixel image is (999,999). So it is
> possible to give a GCP to pixel (1000,1000), that is actually outside of the
> image? Knowing that would have saved me some work.

Jukka,

There is no absolute constraint on GCPs requiring them to be on the image.
In some situations - for instance subsetting a GCP controlled image - it
might make a lot of sense to have GCPs well outside the image.

In any event in the above case (1000,1000) is the bottom right corner
of the bottom right pixel and can be considered on (or on the edge of)
the image.

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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