[GRASS-user] Topological Trouble

James Keener jim at jimkeener.com
Thu Aug 28 13:32:17 PDT 2014


6.4.3 sorry about not including that from the start.

On August 28, 2014 3:42:45 PM EDT, Markus Neteler <neteler at osgeo.org> wrote:
>Jim,
>
>please post your GRASS version to the list to better help.
>
>Markus
>
>On Thu, Aug 28, 2014 at 1:40 PM, James Keener <jim at jimkeener.com>
>wrote:
>> I'm trying to create a map with isolines for the road-distance places
>> are from bus routes.  I was trying to roughly follow
>>
>http://jcastellssala.wordpress.com/2012/05/07/basic-network-analysis-with-grass/
>> but I don't quite get similar results (I feel like the network isn't
>> completely connected, but this is the first time I'm doing this so
>it's
>> more likely I'm just doing it wrong.
>>
>> I am using the following shapefiles in SRID 2272 (NAD83 /
>Pennsylvania
>> South (ftUS)):
>>
>> http://jimkeener.com/grass-topo-question/roads.tar.bz2 which is the
>> TIGER road graph for Allegheny County, PA, USA (state fips = 42,
>county
>> fips = 003), but reprojected to 2272 and a "length" attribute added.
>>
>> http://jimkeener.com/grass-topo-question/stops.tar.bz2 which is
>derived
>> from the Port Authority of Allegheny County GTFS file found at
>>
>http://www.portauthority.org/paac/CompanyInfoProjects/DeveloperResources.aspx
>> and reprojected to 2272.
>>
>>
>> So, the first thing I did is import these files:
>>
>>> v.in.ogr dsn=roads.shp layer=roads output=roads
>>> v.in.ogr dsn=stops.shp layer=stops output=stops
>>
>> (http://jimkeener.com/grass-topo-question/ac.png)
>>
>> Then I connect the stops to the network
>>
>>> v.net input=roads points=stops output=network operation=connect
>thresh=500
>>
>> Connect the require database layer
>>
>>> v.db.connect map=network table=schools layer=2
>>
>> Then allocate the network
>>
>>> v.net.alloc --overwrite --verbose input=network output=network_alloc
>ccats=1-6965
>>
>> (http://jimkeener.com/grass-topo-question/ac-alloc-zoom-thumb.png
>when
>> displayed with d.vect -c) (the little Xs are bus stops
>>
>> And create isolines at 1-, 2-, and 3- thousand feet
>>
>>> v.net.iso --overwrite input=network output=network_isolines
>ccats=1-6965 costs=1000,2000,3000 afcolumn=LENGTH abcolumn=LENGTH
>>
>> (http://jimkeener.com/grass-topo-question/ac-isolines-zoom.png also
>with
>> d.vect -c)
>>
>> All but a few of the roadways near the open space to the right (a
>park
>> and very hilly (even by Pittsburgh standards:-p) area) are within
>3000
>> feet of a bus stop.  Therefor I was expecting almost all of the roads
>to
>> be highlighted in different colors representing their distance from a
>stop.
>>
>> Thank you for any help!
>> Jim
>>
>>
>> _______________________________________________
>> grass-user mailing list
>> grass-user at lists.osgeo.org
>> http://lists.osgeo.org/mailman/listinfo/grass-user

-- 
Sent from my Android device with K-9 Mail. Please excuse my brevity.
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