On 09/07/2020 10:09, Landry Breuil wrote:
On 08/07/2020 13:23, Even Rouault wrote:
On mercredi 8 juillet 2020 10:12:31 CEST Landry Breuil wrote:
<snip>
Your best option with VRT would be to use a NoData value instead if
you can.
You mean setting a nodata value when building the COGs (ie
gdal_translate -a_nodata 0 -of COG dataset.vrt dataset.tif) instead of
the alpha/mask band, and then using this nodata value as -srcnodata 0
parameter to gdalbuildvrt ?
So i tried this nodata method, it sort of works, ie i can stack the COGs
on top of each other via the VRT, and they're blended together at
display time.. unless (and i already hit that in the past) on the
borders of the COG one can see ugly artifacts of the JPEG compression
going 'outside' the original area:
https://imgur.com/t0hwdvx.png
https://imgur.com/RqJXbmx.png
to workaround this in the past, i had built a contraption/script that
'worked' but wasnt fully satisfying:
- creating a geojson with a cutline from the tileindex (ogr2ogr -dialect
SQLITE -f GeoJSON -sql "SELECT buffer(GUnion(GEOMETRY), -12, 1) from
tileindex)
- warping the vrt with the cutline via gdalwarp
- compressing the result via gdal_translate (not COG yet, but TIFF with
JPEG/YCBCR)
- and then adding overviews separately via gdaladdo
i'm unsure this method is still the way to go to eradicate artifacts on
the borders of image, as i had sometimes artifacts *in the overviews*
which were also JPEG-compressed.
Landry
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