[gdal-dev] current geolocation array implementation status

[Frank Warmerdam]

Frederico,

I've updated the ticket to reflect that I backed away from work on a new
implementation.  I would still like to see a reliable geolocation
transformer.

I am also still interested in the general topic of iterative approximate
inverses for transformers which are not inherently invertible.

Best regards,
Frank


On Tue, Nov 2, 2021 at 1:18 PM Even Rouault <even.rouault at spatialys.com>
wrote:

> Frederico,
>
> Le 01/11/2021 à 23:22, Frederico Liporace a écrit :
> > Hello,
> >
> > I'm debugging an artifact that I encountered while using geolocation
> arrays:
> > https://github.com/OSGeo/gdal/issues/4707
> >
> > While searching I found this ticket mentioning that the backward map
> > implementation is broken and a new implementation is being considered:
> > https://trac.osgeo.org/gdal/ticket/6959
> >
> > I could help with this implementation. Is there more context available
> > on why it is being reconsidered? It seems to me that the general case
> > for the backward implementation is very hard - for instance, what kind
> > of discontinuities (gaps, overlaps) would be allowed in the
> > geolocation array? Would it be expected to be robust enough to correct
> > the Landsat 7 ETM+ SLC-off for instance? My guess is not.
>
> Yes the general case is likely hard and would probably require special
> techniques that could possibly be sensor specific. I guess the
> requirements for improvements on the existing code would be at least not
> degrade what works currently.
>
> An idea for a new implementation would be to use an iterative process
> using the backward map as an initial guess and then iterating with the
> bilinear interpolation of the forward path to refine the solution up to
> convergence to some threshold of error to decide (could be 15% of a
> pixel size like the default setting of the gdalwarp approximate
> transformer of coordinate transformations)
>
> Even
>
> --
> http://www.spatialys.com
> My software is free, but my time generally not.
>
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>


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