[GRASS-user] Problem with v.clean and Breaking at Intersections

[Hamish]

Ryan R. Rosario wrote:
> I am having some trouble trying to break road lines from a
> TIGER/Line file at intersections.
> 
> I followed advice in another thread, but I cannot get v.clean to do
> anything useful. I performed the following command equivalents using
> the GUI:
> 
> v.patch input=roads at PERMANENT output=preint

Isn't the point of v.patch to combine two input maps? But you only
list one map there.  ??

> v.clean input=roads at PERMANENT output=tempfile type=line,boundary \
>   error=intersections tool=break
>
> I have verified that GRASS does in fact recognize the shape file as
> containing lines. If I try to display the error vector layer, nothing
> is displayed (because nothing is written to the layer). How can I solve
> this?
....
> Topology was built.
> Number of nodes     :   26669
> Number of primitives:   32493
> Number of points    :   0
> Number of lines     :   32493
> Number of boundaries:   0
> Number of centroids :   0
> Number of areas     :   0
> Number of isles     :   0
> 
> --------------------------------------------------
> 
> Building topology for error vector map...
> Building topology ...
> Registering lines: 
> 0 primitives registered      
> Building areas: 
> 0 areas built      
> 0 isles built
> Attaching islands: 
> Attaching centroids: Topology was built.
> Number of nodes     :   0
> Number of primitives:   0
> Number of points    :   0
> Number of lines     :   0
> Number of boundaries:   0
> Number of centroids :   0
> Number of areas     :   0
> Number of isles     :   0


Well, there may be no features written to the errors map because no errors
were found. ??


If you look at the input and output layers in v.digit do the lines really
cross without nodes?

do the input and output maps have the same number of nodes? (v.info)


Hamish