[GRASS-user] If not v.overlay, what?

[Sylvain Maillard]

2011/7/27 Rich Shepard <rshepard at appl-ecosys.com>

>  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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