[Qgis-user] clip raster by mask layer (gdalwarp with -cutline option) enormously bloats file size

[Pedro Venâncio]

Hi Karsten,

First you have to ensure that the output data type is also Byte:
-ot Byte

Second, your original raster must be some kind of compression. You can see
it with gdalinfo. So, you need to apply compression to the output file, for
instance with:

-co COMPRESS=DEFLATE -co PREDICTOR=2 -co ZLEVEL=9


Best regards,

Pedro Venâncio



karsten <karsten at terragis.net> escreveu no dia sexta, 12/06/2020 à(s) 21:09:

> Hi All,
>
> I have a large *.tif raster data set ( 92000 * 69000 cells of one meter,
> projection EPSG:25832 - ETRS89 / UTM zone 32N )
> It contains integer values 1 to 20 and has a file size of  about 100 MB
> in "Byte - Eight bit unsigned integer" format.
> Now the result is a rectangle and I wanted to cut it down to the area of
> interest (via cutline gdal option) using a shape polygon file (with one
> continuous polygon inside) to and set all values outside the area of
> interest of that rectangle to NULL values (for example setting 0 as NULL
> data values). I used the QGIS ( QGIS v 3.12 on windows) Menu RASTER >
> Extraction > Clip Raster by mask Layer which is based on gdalwarp.
> That is when I am running into the problem that the 'cut' file size
> increases enormously and I ended up wit 50 times bigger file ( 5 GB size
> ! ) when I was actually expecting a smaller file size than before.
> I have not really an idea why the file becomes so enormously bloated. The
> same is the cass when I try gdalwarp directly on the command line or when
> using the QGIS Raster calculator or any other method I tried so far.
>
> How can I manage to get a smaller file size ( aka the 100 MB file size I
> started of with ) and which tools or formats are recommended  to achieve
> this ?
> Cheers
> Karsten
>
> Karsten Vennemann
> www.terragis.net
>
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