[gdal-dev] GeoPDF content inverted as GeoTIF

[Gane R]

Thanks for your timely response. Well the PDF was generated at the source
by different form such that I didn't face this problem, that new version of
the file worked for me.

On Mon, Dec 14, 2015 at 7:20 PM, Even Rouault <even.rouault at spatialys.com>
wrote:

> 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
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