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

[karsten]

Hi Pedro,
 
using your suggestion I came up with this command :
 
gdal_translate -co COMPRESS=DEFLATE -co PREDICTOR=2 -co ZLEVEL=9 -ot Byte
-of GTiff -tr 1.0 -1.0 -a_nodata 0 input.tif output.tif
 
and got the 5GB file cut result raster from before down to 43 MB !
 
Thanks
Karsten

  _____  

From: Pedro Venâncio [mailto:pedrongvenancio at gmail.com] 
Sent: Friday, June 12, 2020 13:19
To: karsten
Cc: QGIS User
Subject: Re: [Qgis-user] clip raster by mask layer (gdalwarp with -cutline
option) enormously bloats file size


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