Le lundi 14 décembre 2015 13:25:13, Rahkonen Jukka (MML) a écrit : > Hi, > > There is something odd in the PDF. It is without coordinate system and > perhaps because of that the top-left coordinates are (0,0) and north > coordinate is increasing from top to bottom. Probably the "Invalid length > for GPTS object" error does not have any effect on this.
It does have an effect. The error messages indicates that the geospatial tags are ignored, thus the non-georeferenced coordinates which are displayed. I've looked at that file a bit and the georeferencing is unusual. It uses Adobe ISO 32000 georeferencing but with only 2 tie-points instead of 4 as usual. The spec doesn't mention the number of tie-points, but the driver assumes 4, based on test samples. It has also unusual MediaBox coordinates (non 0 lower left corner) I've removed locally the limitation and did some fiddling in the code to generalize it, but I don't manage to get a good overlay with a basemap. I can get something roughly in the target area, but there is a rotation term that is clearly missing. But with only 2 tiepoints, the solver of GCPs to geotransform cannot produce any rotation term and assumes linear stretching of coordinates. You have to make assumptions as you've the 6 coefficients of the geotransform matrix to compute, but only 4 equations. In that case, to recover rotation terms, it would probably have to make the assumption that the pixels are square instead (you'd have only 4 unknowns: x,y of top-left corner, pixel size, rotation angle). I didn't investigate further for now. But it seems unwise from the data producer to produce only 2 tiepoints because of the above mentionned ambiguity. As far as I can see, the PDF spec doesn't tell what to do in that case. Even -- Spatialys - Geospatial professional services http://www.spatialys.com _______________________________________________ gdal-dev mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/gdal-dev
