[gdal-dev] GDALWarpAppOptionsNew and GDALWarp usage?

[Even Rouault]

Sean,

This looks fine, except for the argv[0] value, "lolwut". What is that 
supposed to be ? I assume GDALWarpAppOptionsNew() fails on that and 
returns NULL.

The obvious demo for using GDALWarp() is the gdalwarp binary itself: 
https://github.com/OSGeo/gdal/blob/master/apps/gdalwarp_bin.cpp

The COG driver is also a user of it, perhaps more illustrative than the 
above : 
https://github.com/OSGeo/gdal/blob/master/frmts/gtiff/cogdriver.cpp#L552

Even

Le 13/04/2022 à 21:53, Sean Gillies a écrit :
> Hi all,
>
> I'm trying to figure out how to use the GDALWarp function from 
> gdalwarp_lib.cpp. It looks like it takes a pointer to a 
> GDALWarpAppOptions structure that is parsed from a string list, 
> basically gdalwarp's argv, right?
>
> I'm able to get it to warp data, but the options, specifically the 
> resampling option, don't seem to be passed into the warper. The output 
> is the same for all resampling values.
>
> Here's my C usage (Cython, actually, but translates to C).
>
>     cdef GDALWarpAppOptions *warp_options = NULL
>     cdef char **argv = NULL
>     try:
>         argv = CSLAddString(argv, <const char *>"lolwut")
>         resampling_opt_value = Resampling(resampling).name # like 
> "bilinear"
>         argv = CSLAddString(argv, <const char *>"-r")
>         argv = CSLAddString(argv, <const char *>resampling_opt_value)
>         ...
>         CSLPrint(argv, NULL)
>         warp_options = GDALWarpAppOptionsNew(argv, NULL)
>         output_ds = GDALWarp(
>             NULL,
>             dst_dataset,
>             1,
>             src_datasets,
>             warp_options,
>             NULL
>         )
>     finally:
>         ...
>
> The printed output, my argv, is
>
>     lolwut
>     -r
>     bilinear
>
> Does GDALWarpAppOptionsNew expect more values at the head of the 
> command line? Is that why it is missing "-r"? Or is my string list 
> made up of the wrong kind of strings? Documentation examples of 
> building the arguments for GDALWarp are scarce. I'd be super grateful 
> for help from anyone who has got code this to work.
>
> Thanks,
>
> -- 
> Sean Gillies
>
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> gdal-dev mailing list
> gdal-dev at lists.osgeo.org
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