[gdal-dev] mosaicking files with partial overlap and binary mask

[Daniele Romagnoli]

Hi Jukka,
sorry but I can't share the data. Is owned by a customer :(

Long story short:
I have several raster tiles (with size around 5000x5000) and a shapefile
containing edges defining valid area of each tile.

I have used gdalrasterize to extract the needed crop for each tile to setup
a binary mask.
Then, I have combined the binary mask with the original tile and rewritten
as a new TIFF file with internal masks.
Then, I'm composing all the TIFF files to a VRT.
When rewriting that VRT to a mosaic TIFF, everything looks good. I see the
binary mask is used to properly compose/overlap/mask the pieces of the
mosaic and the output contains the mask too. This is an example of gdalinfo
on one of the mosaicked tiff:

Driver: GTiff/GeoTIFF
Files: out.tif
Size is 45842, 42506
Coordinate System is:
[... OMITTED... ]

Metadata:
  AREA_OR_POINT=Area
Image Structure Metadata:
  COMPRESSION=YCbCr JPEG
  INTERLEAVE=PIXEL
  JPEGTABLESMODE=1
  JPEG_QUALITY=75
  SOURCE_COLOR_SPACE=YCbCr
Corner Coordinates:
  [... OMITTED... ]
Band 1 Block=256x256 Type=Byte, ColorInterp=Red
  Mask Flags: PER_DATASET
Band 2 Block=256x256 Type=Byte, ColorInterp=Green
  Mask Flags: PER_DATASET
Band 3 Block=256x256 Type=Byte, ColorInterp=Blue
  Mask Flags: PER_DATASET

So, as you can see the masks are added to the mosaicked dataset.

However, when running
gdalwarp -t_srs EPSG:NEWCODE out.tif warped.tif

the binary mask is lost from the output file.
I have also tried using -dstalpha but it complains that "Destination
dataset has 3 bands, but at least 4 are needed" which makes sense.

So I was just wondering if there is anything I should be aware of when
warping a masked TIFF.
I would probably try to transform the binary mask to an alpha band, do the
warp and then convert back the alpha to a binary mask....

Thanks for any feedback in advance.
Regards,
Daniele





On Thu, Feb 11, 2021 at 3:27 PM jratike80 <
jukka.rahkonen at maanmittauslaitos.fi> wrote:

> Hi Daniele,
>
> Test data, please.
>
> -Jukka Rahkonen-
>
>
>
> Daniele Romagnoli-3 wrote
> > Thanks for the feedback, Patrick.
> > I have downloaded the latest build from GisInternals and it worked as
> > expected.
> > I have another question.
> > It looks like warping an input file containing a binary mask isn't
> > preserving the binary mask on the output.
> > Should I specify any flag for that?
> >
> > Thanks for the help.
> > Regards,
> > Daniele
> > _______________________________________________
> > gdal-dev mailing list
>
> > gdal-dev at .osgeo
>
> > https://lists.osgeo.org/mailman/listinfo/gdal-dev
>
>
>
>
>
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-- 
Regards,
Daniele Romagnoli
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Ing. Daniele Romagnoli
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