Le jeudi 14 novembre 2013 21:24:01, Trent Piepho a écrit : > On Nov 10, 2013 1:44 AM, "Even Rouault" <even.roua...@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 -- Geospatial professional services http://even.rouault.free.fr/services.html _______________________________________________ gdal-dev mailing list gdal-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/gdal-dev