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

[Johannes Sommer]

Hi Markus,

I 'll write a FAQ when I get correct results from the process of network
service area. David's approach of using v.net.salesman on a
delauany-graph worked for a few special geometries. But I think the
results are not really good for many cases.
I' ve got an idea about another solution but it's not fully tested yet.

The problem of automatically finding the endpoints as Richard mentioned
it will also be part of the research.
More on this when I have more time to work on this.

regards,
Johannes


Markus Neteler schrieb:
> 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
>>>>>
>>>>> _______________________________________________
>>>>> grass-user mailing list
>>>>> grass-user at lists.osgeo.org
>>>>> http://lists.osgeo.org/mailman/listinfo/grass-user
>>>>>
>>>>>
>>>>>           
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