[gdal-dev] gdalwarp -rpc with RPC_DEM default behavior not as described

[Even Rouault]

Patrick,

Thanks for the report. It was indeed not working as documented. Fixed per 
https://trac.osgeo.org/gdal/ticket/6608

Even

> Hi all,
> 
> We've been making some orthos with gdalwarp (gdal version 2.1.1) and
> encountering resampling errors in the output (gittery output in the lines
> in certain spots).  Long story short, explicitly setting the "-et" option
> to "0" fixed it, but the docs for gdalwarp say the following (under the -et
> flag description):
> 
> "starting with GDAL 2.1, the RPC_DEM warping option is specified, in which
> case, an exact transformer, i.e. err_threshold=0, will be used"
> 
> Here's an example of the call we're making where we see the artifacts:
> 
> gdalwarp -t_srs EPSG:3857 -rpc -to RPC_DEM=dem.tif in.tif out.tif
> 
> and this guy fixes it:
> 
> gdalwarp -et 0 -t_srs EPSG:3857 -rpc -to RPC_DEM=dem.tif in.tif out.tif
> 
> I'm guessing the flag is not actually being set, but if anyone can point me
> to the code where this default is supposed to be set when the dem is
> specified, I might be able to provide a fix or figure out that I'm doing it
> wrong!  I didn't have much luck searching through the github archive.
> 
> Thanks!
> 
> -Patrick

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