[GRASS-user] Topological Trouble

GRASS GRASS user
1

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

2

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@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

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3

6.4.3 sorry about not including that from the start.

On August 28, 2014 3:42:45 PM EDT, Markus Neteler neteler@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@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](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](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](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](http://www.portauthority.org/paac/CompanyInfoProjects/DeveloperResources.aspx)
>  and reprojected to 2272.
> 
>  So, the first thing I did is import these files:
> 
> > [v.in](http://v.in).ogr dsn=roads.shp layer=roads output=roads
> >  [v.in](http://v.in).ogr dsn=stops.shp layer=stops output=stops
> 
>  ([http://jimkeener.com/grass-topo-question/ac.png](http://jimkeener.com/grass-topo-question/ac.png))
> 
>  Then I connect the stops to the network
> 
> > [v.net](http://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](http://v.net).alloc --overwrite --verbose input=network
> > output=network_alloc ccats=1-6965
> 
>  ([http://jimkeener.com/grass-topo-question/ac-alloc-zoom-thumb.png](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](http://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](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@lists.osgeo.org
>  [http://lists.osgeo.org/mailman/listinfo/grass-user](http://lists.osgeo.org/mailman/listinfo/grass-user)

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

4

On Thu, Aug 28, 2014 at 10:32 PM, James Keener <jim@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@osgeo.org> wrote:

...

On Thu, Aug 28, 2014 at 1:40 PM, James Keener <jim@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

5

Thanks for replying Markus,

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:

I know. For testing purposes it seemed to be reasonable, though
(increments of 1000 ft. For my final map I'll probably do 1/4mi, 1/2mi,
3/4mi, and 1mi increments).

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).

I spot checked a lot of the bus stops, and they appeared to be connected
to the road graph. FWIW. The TIGER road maps do appear to make
intersections overlap, but don't put a point that all the adjoining
roads connect to. (This brings up something I was going to worry about
later: bridges vs intersections?)

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?

I'll have to give GRASS 7 a shot:) (GRASS 6 is what was in the repo I
was using).

I'm completely new at this so the biggest problem for me is not know
exactly where to look when something isn't working.

Thanks again for your input!

Jim

6

Hello,

I wrote a tutorial on how to go from a TIGER road map and GTFS data to a
topological analysis of bus stops. There are some minor formatting
issues I'm working on, but was hoping to get technical or other feedback
on it.

http://jimkeener.com/posts/analyizing-bus-routes

Thank you,
Jim

7

Jim,

I’ll try to find some time to work through your tutorial in the next few days; I’ll get back to you – I just took a quick look and I think it looks good. BTW, I’m also using Ubuntu (14.04).

Tom

···

On Thu, Sep 11, 2014 at 11:29 PM, James Keener <jim@jimkeener.com> wrote:

Hello,

I wrote a tutorial on how to go from a TIGER road map and GTFS data to a
topological analysis of bus stops. There are some minor formatting
issues I’m working on, but was hoping to get technical or other feedback
on it.

http://jimkeener.com/posts/analyizing-bus-routes

Thank you,
Jim

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