[Gdal-dev] Irregular geolocation grid

[Eric Dönges]

Am 16.04.2004 um 23:28 schrieb Frank Warmerdam:

> However, keep in mind that a polynomial transformation does not 
> necessarily
> map the underlying relationship all that well.  All we really know is 
> that
> how to transform the points at the GCPs.

I've found this out the hard way recently using a 5th order polynomial 
on a
fairly large scale Mercator projection - the GCPs are matched almost 
perfectly,
large portions of the rest of the map are mapped completely wrong =8^(.

> It was my intention that GDALGCPstoGeoTransform() would be corrected
> to do a first order best fit approximation based on all the GCPs at 
> some
> point.  If you have a reasonly clean implementation of this feel free 
> to
> provide it.

I've attached a patch to gdal_misc.cpp to this mail. It gives 
reasonable results
for the maps I've tried it with, but I'm no expert on numerics, so 
there may be
better ways to structure the code to avoid rounding errors.

Best regards,
Eric

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