I went through this last year, and as I remember, v.hull doesn't quite get you there, since the resultant polygon can't "dip in" to reach concave sections of a service area. I used v.delaunay to create a network of the nodes that made up the connections between service areas, and v.net.salesman to generate the edges of the service areas.
David On Mon, 2010-04-05 at 09:04 -0300, Daniel Victoria wrote: > If I understand you correctly, v.hull might help to create the service > area polygon from the points.... > > http://grass.itc.it/grass62/manuals/html62_user/v.hull.html > > On Sun, Apr 4, 2010 at 8:12 PM, Richard Chirgwin > <[email protected]> wrote: > >> > >> ------------------------------ > >> > >> Message: 3 > >> Date: Sat, 03 Apr 2010 23:11:26 +0200 > >> From: "Johannes Sommer" <[email protected]> > >> Subject: [GRASS-user] v.net.iso - service area > >> To: [email protected] > >> Message-ID: <[email protected]> > >> Content-Type: text/plain; charset="iso-8859-1" > >> > >> Hi list, > >> > >> recently I played around with the network functionality in ArcGIS. I > >> generated so called "Service Areas" in a network dataset which return the > >> regions that can be accessed in a network dataset based on several > >> distances > >> (in my example 150, 400 meters). > >> > >> I wanted to reproduce the results with GRASS GIS and after a short search > >> I found the module v.net.iso which seemed to fit my needs. It returns > >> exactly the same results as ArcGIS did on isolines on a network, but I > >> can't > >> find any solution concerning the service areas. > >> > >> Can anyone point me in the right direction to calculate zones (that is > >> "build polygons from the end points of each network segment") from these > >> generated isolines in a network? > >> > >> Regards, > >> > >> Johannes > >> > >> > >> > > > > Johannes, > > > > I don't think there's anything to do this automatically in Grass-GIS. But I > > think you should be able to construct a script that would connect pairs of > > points. > > > > So if you can extract each end point of the network segment, you would end > > up with a vector containing only points - then create a temporary map of a > > point pair, run (say) v.distance output=connectors on each point pair, patch > > the resulting maps together ... > > > > It sounds a bit labourious, and probably someone else can think of something > > easier, but if you get all the individual steps right, a script is then easy > > to create. > > > > (Actually, Johannes, I think the idea is brilliant. I've done lots of > > network service area work, and it never occurred to me before!) > > > > Richard Chirgwin > > > > _______________________________________________ > > grass-user mailing list > > [email protected] > > http://lists.osgeo.org/mailman/listinfo/grass-user > > > _______________________________________________ > grass-user mailing list > [email protected] > http://lists.osgeo.org/mailman/listinfo/grass-user _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
