I want to vectorize that rasterfile with its 6 landuse classes. The classification is very noisy and have to be generalized before.
The result should be a polygone vector file.
I use SAGA, (GRASS) and QGIS.
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To simplify the raster it might be worth looking at gdal_sieve, it's available under the "Raster" menu. See: http://www.gdal.org/gdal_sieve.html
To generalize, try running a majority filter. This is available in saga (and grass as well, check markusN his answer). An explanation for how it works from arcgis: http://edndoc.esri.com/arcobjects/9.2/net/shared/geoprocessing/spatial_analyst_tools/majority_filter.htm
you can use gdal_polygonize.py for converting raster to vector, if u previously use . some information is here.
produces a polygon feature layer from a raster
gdal_polygonize.py [-o name=value] [-nomask] [-mask filename] raster_file [-b band] [-q] [-f ogr_format] out_file [layer] [fieldname]
beside this in qgis you can use Polygonize tool for your needs. it is under the
Raster > Conversion > Polygonize (Raster to vector) menu.
if u dont see anything except Raster Calculater under Raster menu, you have to enter Manage Plugins under Plugins, then enable GdalTools. that is all..
i hope it helps you...
Using the majority filter with a kernel of 5 by 5 pixels gives the best results for me.