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

[Micha Silver]

On Fri, 2011-07-29 at 06:42 -0700, Rich Shepard wrote:

> On Fri, 29 Jul 2011, Micha Silver wrote:
> 
> > Use "AND" not "OR".
> > OR=Union, that is combining all features of both vectors
> > AND=Intersection, that is, just areas or lines covered by both vectors
> 
> Micha,
> 
>    That's correct, and 'AND' will exclude those portions of the drainage
> basins that extend past the property boundary. That's why I used 'OR' to get
> all points within both the basins and the property. Two extremes. :-) What
> I'd like to do is select only those basins that intersect the property, but
> all of those basins, and get rid of the other 4200+ basins that are
> irrelevant to the analyses.


Is the "property" also polygon vector ? Then do a v.overlay with the
drainage basins and the property again using the "AND" operator . That
should leave you with only the basins in the property.

Now for the streams, merge all the resulting few basins that are inside
the property into one with i.e v.dissolve. 
To do this You will have to add a temp column and populate it with some
temp value, identical for all those few basins, as the dissolve column.
The value '1' would be fine... . And last do another v.overlay with this
new dissolved basin vector and the streams layer to get those streams
within the property and within the basins.


> 
>    I seem to have issues with client- and agency-provided data on my
> projects. But, once I successfully make the data available to grass and
> define the appropriate computational and display regions, the modeling goes
> more smoothly.
> 
> Thanks,
> 
> Rich
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