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.
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.
I have another issue with the DEM, but that will be on a separate thread.
Rich
[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.
On Wed, 2011-07-27 at 14:42 -0700, Rich Shepard wrote:
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
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
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.
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.
I have another issue with the DEM, but that will be on a separate thread.
Rich
[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.
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2011/7/27 Rich Shepard <rshepard@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
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.
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
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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