+1 for GRASS Hartanto Sanjaya has a nice slide for calculating a basic volume for a lake using GRASS.
May help if you are unfamiliar with the tools available in GRASS. http://hartanto.wordpress.com/2007/06/16/analisis-3-dimensi-untuk-volume-air-danau/ mars On Tue, Nov 15, 2011 at 11:01 AM, Saber Razmjooei <[email protected] > wrote: > I had this problem in the past. Unfortunately there are not many plugins > for raster analysis in QGIS and I usually I end up doing in in GRASS. > The command in GRASS for inspection your raster layers, using polygon > vectors: > http://grass.osgeo.org/gdp/html_grass64/v.what.rast.html > > You need to run r.null to set the unwanted values to null (i.e. positive > or negative values). > > > Cheers > Saber > > On Tue, 2011-11-15 at 18:57 +0100, Bernhard Draeyer wrote: > > I have 2 high resolution raster DEM's before and after a recent flood > > event. The aim would be to get for different areas a) erosion/negative > > volumes b) accumulation/positive volumes and net volume. > > > > First of all, i subtracted the actual surface from the 'before'-surface > > to get a difference surface with positive (accumulation) and negative > > (erosion) values. > > Then i created a shape layer with polygons of different areas of > > interest. For each of them i need seperate volumetrics. Ideally, the > > polygons should contain in the end attribute values for accumulation, > > erosion and net volumes. > > Now i was looking without success for a well adapted method to solve my > > problem in QGIS or SAGA. > > > > How should i proceed? Is there any method in QGIS to sum up positive and > > negative raster values under polygons and put them in seperate attribute > > fields per polygon? Do i have to convert the raster in a point layer? I > > saw, that in esri's 3d analyst exist a tin polygon volume function, that > > covers this task. Does anything similar exist with an os gis? > > > > > > Many thanks for your help. > > > > Bernie > > > > _______________________________________________ > > Qgis-user mailing list > > [email protected] > > http://lists.osgeo.org/mailman/listinfo/qgis-user > > > _______________________________________________ > Qgis-user mailing list > [email protected] > http://lists.osgeo.org/mailman/listinfo/qgis-user >
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