[GRASS-user] Construction in grass

[Craig Leat]

Hi Torsten

Torsten Eckart wrote:
> Hallo,
> could anyone give me a hint how to construct in grass on the
> best way? I want to draw  dams  in an drainage stream system ,  they
> have to have especial withs and heights. How to construct the streams
> the best way?Than I want to calculate the amount of material what is to
> move there to build the dams from natural material of that area.
> Possible to export as .dxf and work in qcad?
> Could someone gives me some links in the net?

You can calculate the dam wall volume, water volume and water surface
area using raster map algebra. GRASS has various interpolation methods
to create a surface from vector points. You would create three DEMs to
represent the original ground surface, the dam wall surface and the
water surface. Subtract the ground map from the wall map, set all
negative values to zero, then sum all values in the resulting map and
multiply by the cell area to get the volume of the wall. You could
then create a polygon from this difference map, representing the
wall's footprint and export it as dxf for further work in CAD.

Craig