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

[karsten]

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
 <http://www.terragis.net> www.terragis.net
 
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