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.roua...@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. > > _______________________________________________ > gdal-dev mailing list > gdal-dev@lists.osgeo.org > https://lists.osgeo.org/mailman/listinfo/gdal-dev > -- ---------------------------------------+-------------------------------------- I set the clouds in motion - turn up | Frank Warmerdam, warmer...@pobox.com light and sound - activate the windows | +1 650-701-7823 and watch the world go round - Rush | Geospatial Software Developer
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