[gdal-dev] GDALApplyGeoTransform

[Andrew Bell]

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.  The GeoTiff spec (see 2.5.2.2) says that this behavior is
the default unless the key GTRasterTypeGeoKey is set to
RasterPixelIsPoint.

Then I found this:
https://trac.osgeo.org/gdal/wiki/rfc33_gtiff_pixelispoint which was
supposed to address this issue, but I'm not sure it was implemented or
how.

Anyway, I'm not sure what's supposed to happen and I'm not sure why I
should have to manually adjust a pixel's position when converted to a
geolocation rather than expect the correct value to be generated by
GDALApplyGeoTransform.

Of course, I may well be missing something, so please correct me if I am.

Thanks,

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