[Gdal-dev] GetGeoTransform/png bug?

[Frank Warmerdam]

On 4/14/05, Kor de Jong <k.dejong at geo.uu.nl> wrote:
> Hi list,
> 
> I am using GetGeoTransform, and according to the documentation "The default
> transform is (0,1,0,0,0,1) and should be returned even when a CE_Failure
> error is returned, such as for formats that don't support transformation to
> projection coordinates.". When my application loads a png file
> GetGeoTransform returns CE_Failure but the transform coefficients are not set
> to (0,1,0,0,0,1). I guess this is a bug in the png driver? As another
> example, the GIF driver does return (0,1,0,0,0,1).

Kor, 

This is a failure of the png driver to follow the specification, though in 
practice I have found it is dangerous to depend on the geotransform
in cases where the fetch fails as driver implementors often do this
aspect incorrectly (as I did for PNG).  

This will hopefully get corrected by my current efforts to implement
"persistant auxilary metadata" support in a driver generic way.   It has
already corrected it for the PNG driver which I am using as a test of the
new mechanisms. 

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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and watch the world go round - Rush    | Geospatial Programmer for Rent