David, thank you very much! I tested your approach with network isolines derived from a dataset with one center - and it worked very well! The automated approach will be interesting (also with more than one center) - but therefore I need more experience in GRASS scripting.
thanks, Johannes David Mahoney schrieb: > 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 > > _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
