[gdal-dev] current geolocation array implementation status

[Even Rouault]

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

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