[gdal-dev] geotiff projection not showing up

[Even Rouault]

Le jeudi 14 novembre 2013 21:24:01, Trent Piepho a écrit :
> 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.

You can use gdalwarp to transform a dataset with GCPs to a dataset with 
geotransform. gdalwarp uses the GDAL warping API : 
http://www.gdal.org/warptut.html


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