Filtering a raster by pixel value ? (Qgis)

Question

I have downloaded Globcover data in GeoTIFF format. I want to create a new grid which only has values where the Globcover data (the only band in the TIF file) has one certain value (==190).

Can I do this with GDAL?

If not, which way should I go? The procedure should be callable from a Shell script (Linux). I have QGIS installed (but no clue how to use it).

Answer 1

In QGIS you have the raster calculator (Under the "Raster" menu) which will do what you want. (not a shell script command)

• Load your Globcover raster into QGIS, and open the Raster Calculator.
• The raster will appear in the "Bands" window.
• Enter a name for the new "Output Layer".
• Now double click on the Globcover band name so that it appears in the lower "Raster calculator expression".
• Then complete the expression by typing "=190" in that window.
• Click OK to create the new raster.

Note that you will have a raster with values of either 190 or 0 everywhere else. You can further use gdal_translate to set the zeros to NULL.

HTH, Micha