David,
I'd just like to confirm the process ...
1. Obtain points you wish to use as the service area edge nodes (I will
call this vector "Limit").
2. Run v.delaunay to create a vector that includes the outline
(map=Delaunay).
3. Run v.net to connect Limit to Delaunay (map=Network)
4. Run v.net.salesman on Network to create the final service area map.
This seemed to work fine for me in Spearfish.
One question - I created the "point set" manually. But if have a network
of lines, what's the best way to create a point vector from the line ends?
Richard
Markus Neteler wrote:
Hi,
would you mind to write a smal FAQ for us?
http://grass.osgeo.org/wiki/Faq
Thanks
Markus
On Fri, Apr 9, 2010 at 2:51 PM, Johannes Sommer <[email protected]> wrote:
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
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