[gdal-dev] GDALApplyGeoTransform

[Andrew Bell]

On Wed, Feb 17, 2016 at 4:12 AM, Even Rouault
<even.rouault at spatialys.com> wrote:
> Le mercredi 17 février 2016 00:23:26, Andrew Bell a écrit :
>> Hi,
>>
>> I'm trying to understand why GDALApplyGeoTransform behaves as it does.
>> I would think that when you use it to transform a raster coordinate to
>> a geo coordinate, it would apply what is known about the raster and
>> the transformation to get the correct location.  What I see happening
>> is some drivers is an adjustment to "center" the points in the middle
>> of a raster cell.  This is fine, but I don't understand why
>> GDALApplyGeoTransform doesn't do this if this is always the proper
>> operation.
>
> GDALApplyGeoTransform() doesn't do this, as adjusting to pixel center or pixel
> top-left corner depends on the convention of each driver (and for some drivers
> like GTiff, both conventions can exist depending on datasets), so the logic is
> in driver code.

But given a GDAL raster and it's associated SRS/transformation matrix,
how do I know if the 1/2 pixel offset should be applied to arrive at
the proper geolocation?  Do rasters internally to GDAL always follow
one or the other of PixelIsArea or PixelIsPoint?

Thanks,

-- 
Andrew Bell
andrew.bell.ia at gmail.com