[GRASS-user] Topological Trouble

[Markus Neteler]

On Thu, Aug 28, 2014 at 10:32 PM, James Keener <jim at jimkeener.com> wrote:
> 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:
...
>> 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/

(nice tutorial, btw)

Note that their projection is in meters, while...

>>> I am using the following shapefiles in SRID 2272 (NAD83 / Pennsylvania
>>> South (ftUS)):

... your's is in US feet (http://epsg.io/2272).
This affect the threshold you use below:

...
>>>  So, the first thing I did is import these files:
...
>>>  Then I connect the stops to the network
>>>
>>>>  v.net input=roads points=stops output=network operation=connect
>>>> thresh=500

Note that the threshold is specified in map units (so, here feet in your case).

Sidenote: in GRASS GIS 7 the module is a bit more advanced:
http://grass.osgeo.org/grass70/manuals/v.net.html

Perhaps (guessing, I didn't have time to test your data), the initial
threshold makes the difference?

Best,
Markus