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

[Sam Snellings]

Fantastic, that worked perfectly. Thanks for taking a look at the data for
me. It didn't even occur to me that the data might have a third dimension.

Is there an easy way to check whether a geometry/shapefile has a
Z-coordinate element in case I run into a similar issue in the future? I
can just test import as 2d as you recommend (or QGIS has an export function
that removes z-coordinates), but perhaps there is an easier way to tell?

-Sam

On Thu, Oct 6, 2016 at 3:32 PM, Markus Metz <markus.metz.giswork at gmail.com>
wrote:

> On Wed, Oct 5, 2016 at 3:05 AM, Sam Snellings <ssnellings at gmail.com>
> wrote:
> > 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.
>
> thanks for providing a link to the data! The problem is that the roads
> are 3D with z coordinates not matching at the end of a road segment
> and the beginning of another road segment. The solution is to import
> roads as a 2D vector with v.in.ogr -2. 2D snapping with v.clean
> tool=snap thresh =1 might be helpful.
>
> Markus M
>
> >
> > -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
> >
> >
> >
> > _______________________________________________
> > grass-user mailing list
> > grass-user at lists.osgeo.org
> > http://lists.osgeo.org/mailman/listinfo/grass-user
>
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