[Qgis-user] volume calculations in qgis

[Mars Sjoden]

+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 <razmjooeis at faunalia.co.uk
> 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
> >
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>
>
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