[gdal-dev] GDALCreateWarpedVRT and .msk files

[sean]

On Fri, Jun 1, 2018 at 7:14 PM, Even Rouault <even.rouault at spatialys.com>
wrote:

> On vendredi 1 juin 2018 18:25:27 CEST Sean Gillies wrote:
> > Hi Even,
> >
> > I got waylaid in following up, but am finally doing so now. Yes, I can
> also
> > confirm that the .msk file is being read over the internet. I'm grateful
> > for the CURL logging in GDAL, it's very handy.
> >
> > However, I'm perplexed by not being able to get the mask I expect from
> the
> > warped VRT I'm creating using GDALAutoCreateWarpedVRT. The source file
> has
> > a mask, but no mask materializes in the warped VRT. I have a WarpedVRT
> > class in Rasterio that calls GDALAutoCreateWarpedVRT and is equivalent to
> > the Python GDAL code you showed. It has a method that calls
> > GDALGetMaskFlags and here's what that reports.
> >
> > with rasterio.open('https://oin-hotosm.s3.amazonaws.com/
> > 5a324a622553e6000ce5aaf5/0/3fa181a1-425c-4e53-b49f-ea72884da097.tif') as
> > src, WarpedVRT(src, dst_crs=src.crs) as vrt:
> >     print(vrt.mask_flag_enums)
> >
> > # Output:
> > # ([<MaskFlags.all_valid: 1>], [<MaskFlags.all_valid: 1>],
> > [<MaskFlags.all_valid: 1>])
> >
> > The source has a per-dataset mask, but this doesn't surface in the VRT.
> It
> > reports that all the pixels are valid.
>
> Hi Sean,
>
> OK I now understand what you meant. The warper in general in GDAL (so not
> specific to the VRT warping) can use the mask of the input dataset, but
> doesn't generate one in output. However it should be able to generate an
> alpha
> band if you call GDALCreateWarpedVRT() with psOptions->nDstAlphaBand = 4
> (couldn't test easily, but hopefully should work)
>
> Even
>

After setting that warp option and setting the color interpretation of the
resulting band to GCI_AlphaBand, I'm in business!

Thanks, Even!

-- 
Sean Gillies
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/gdal-dev/attachments/20180602/2d74e1e4/attachment.html>