2011/7/27 Rich Shepard <[email protected]> > I have a map of drainage basins and another of the project property > boundary. Of the 4200+ basins in the map, the property is in only a dozen > or > so. I'm trying to overlay these maps to produce a union that has only those > basins that drain the property. v.overlay with operator=or yields a > combined > map of _all_ basins and the property[1] so either I'm not correctly > applying > the module, or the resulting map needs more processing with a different > module. Please point me in the right direction to get the results I want. >
there are different ways for that job, one is using r.water.outlet which compute the drainage area for a specified point: get to coordinates of the outlet point of your drainage area, and it will compute one unique corresponding catchment area ! > After I have a map containing only those basins overlaid by the property > boundary I want to use v.overlay to clip the stream networks in these same > basins. I assume that v.overlay with op=and will do this nicely. My > question > is then what process will allow me to extract each drainage basin with its > stream network and portion of the property for terrain and hydrological > analyses and modeling. > transform the resulting catchment area raster into an area vector (r.to.vect), then use v.select or v.overlay to query the stream netwok that is contains into the cathment area ... [1] Using the wxPython GUI with v.overlay I did not see a data entry widget > to select the operator. It apparently defaults to 'or' but if there's a > radiobox to select 'or,' 'and,' 'not,' or 'xor' I did not see it. > in the command dialog box, there are several tabs. One is called "Options", and there is a list box "Operator defines features written to output vector map" which permit to select the different avaliable operator ... Sylvain
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