clipqgisraster
I need to cut a raster layer (size 500 MB about) using a vector mask.
Going to Raster -> Extraction -> Clipper and using a vector mask in the same coordinate system of the raster, QGIS produces a .tiff raster bigger than the original raster (about 1.5 GB) and without the two and .prj file.
I cannot explain this: is there a way to have a clipped raster smaller than the original one and with the two and .prj associated files?
Note that clipper tool (from raster menu) distort your output, or may distort it by changing cell size. My suggestion is to use the clipper under gdal tools from the toolbox.
There define -tr resx, resy in the additional parameters window; where both resx & resy > 0. Those stand for the input raster resolution, and forces the output to keep it. You can get the resolution from the properties>metadata of your input raster. Note that it will be written like this: 30.0, -30.0; thus modify it to be 30.0, 30.0.
The image below sum it up with an example:
The Clipper tool makes an uncompressed image by default. Read the GDAL manual of your format and add manually the compression options into the gdal_translate command that is shown in the lowest pane.
For example for GeoTIFF read http://gdal.org/frmt_gtiff.html and use for example-co COMPRESS=DEFLATE -co PREDICTOR=2 which gives a well compressed, lossless output for topographic maps.
If you think that it would be trivial to add compression options to the user interface of the Clipper tool it is not because more than 30 formats are supported for the output and all of them have different settings for compression if compression is supported at all.
Best Answer
The clipped raster is an uncompressed GeoTIFF (no projection file needed), so you should edit the
gdalwarpstring manually in theClipperwindow to set the compression method (and other useful options). For instance: