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

Patrick Young patrick.mckendree.young at gmail.com
Tue Jul 26 09:40:23 PDT 2016

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.


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