[GRASS-user] v.net.alloc having difficulty with specific dataset

[Sam Snellings]

Markus,

Thank you for the suggestions. I ran the following commands nine times on
the data, with thresholds .00000000000000000001, 0.0000000001,
0.0000001, 0.00001, 0.01, 0.1, 1, 10, and 100. Let me know if I'm not going
small enough.

v.clean --overwrite input=roads output=roads_snap -c tool=snap thresh=[see
above]
v.net --overwrite input=roads_snap points=schools output=network
operation=connect thresh=1000
v.net.alloc --overwrite input=network output=network_allocation ccats=1-2

I did not get a complete allocation of road segments from any of them, and
as far as I can tell it got stuck at the same vertices on each run.

I will email you a link to the data off-list, thanks for taking a look.

-Sam

On Tue, Oct 4, 2016 at 3:53 PM, Markus Metz <markus.metz.giswork at gmail.com>
wrote:

> On Tue, Oct 4, 2016 at 5:09 PM, Sam Snellings <ssnellings at gmail.com>
> wrote:
> > I've been running some trials through v.net.alloc using town road
> networks
> > as the arc layer and schools as the node layer. I have one set of
> > roads/schools that breezes through v.net.alloc without issue (Town 1),
> while
> > another one only allocates the first few arcs connected to each school
> and
> > leaves the rest of the network unallocated (Town 2). There is probably a
> > problem with the data from Town 2, but I can't figure out what it is.
> Does
> > this issue sound familiar to anyone?
> >
> > I am using the GUI. I load each pair of shapefiles into GRASS and then
> run
> > the following statements (I only import two school points to simplify).
> The
> > two towns are pulled right from the state-wide GIS office, but the towns
> are
> > in different states (ie - different agencies provide the data).
> >
> You do not need this for v.net.alloc:
> > v.net input=roads output=road_nodes operation=nodes
> it will create a point for every node, the first point will have
> cat=1, the second cat=2 which collides with the points you want to
> attach
>
> > v.net input=road_nodes points=schools output=network operation=connect
> > thresh=1000
>
> rather use
> v.net input=roads points=schools output=network operation=connect
> thresh=1000
>
> > v.net.alloc input=network output=network_allocation ccats=1-2
>
> the real problem is probably a data problem: roads are not properly
> connected, i.e. the end of one road does not match the beginning of
> another road. Try v.clean input=roads output=roads_snap -c tool=snap
> with a very small threshold. This kind of error is quite common with
> shapefiles (not a fault of the shapefile format but of the software
> used to create the shapefiles).
>
> >
> > Thanks in advance for any advice, I can also email images/data if that
> would
> > be helpful.
>
> If v.clean -c tool=snap does not help, (links to) original data of the
> schools and road network for Town 2 would be helpful (data please only
> off-list).
>
> Markus M
>
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