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

[Markus Neteler]

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 <johann.online at gmx.de> 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
>>> <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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