[GRASS-user] v.net.iso - service area

[Johannes Sommer]

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
>> <rchirgwin at ozemail.com.au> wrote:
>>     
>>>> ------------------------------
>>>>
>>>> Message: 3
>>>> Date: Sat, 03 Apr 2010 23:11:26 +0200
>>>> From: "Johannes Sommer" <Johann.online at gmx.de>
>>>> Subject: [GRASS-user] v.net.iso - service area
>>>> To: grass-user at lists.osgeo.org
>>>> Message-ID: <20100403211126.313360 at gmx.net>
>>>> 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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>>>
>>>       
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