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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