[gdal-dev] geotiff projection not showing up

[Trent Piepho]

On Nov 10, 2013 1:44 AM, "Even Rouault" <even.rouault at mines-paris.org>
wrote:
>
> Le dimanche 10 novembre 2013 00:14:42, Trent Piepho a écrit :
> > I've found that unless you call SetGeoTransform() and give an affine
> > transform, most apps, including listgeo and gdalsrsinfo, aren't
> > entirely happy with the georeferencing.  GDAL has a function that
> > computes a transform from GCPs, but it needs to be part of the GDAL
> > code for the dataset driver.  GDAL doesn't automatically do it when a
> > user of GDAL wants an affine transform from a dataset.
>
> True. This is (I think) a design decision, as generally GDAL tries to
expose
> information as close as possible to what is in the dataset. GCPs alone
don't
> provide an unambiguous way of transforming image pixel coordinates into
real-
> world coordinates. You have to specify which extrapolation method you
want to
> use : polynomial at which order, thin plate spline, ..

>From what I've seen many apps just want to translate between pixel,line and
geographic coordinates.  The method to do this appears to be to get the SRS
from the dataset, use one of it's methods to transform between geographic
coordinates and projected coordinates, then get the geotransform
coefficients and preform the affine transform with them.

With no geotransform, this doesn't work.  Instead one is supposed to....I
don't know.  I don't see any OGR or dataset function that will do the
coordinate transform.  I've looked at other apps, and none of them can
handle this.   So you end up with the only way to georeference a dataset,
and have anything work, is to use a affine transform.
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