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

GRASS GRASS user
1

Hi,

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@PERMANENT output=preint
v.clean input=roads@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?

Your help is greatly appreciated.

Thanks,
Ryan

--------------------------------------------------

Tool: Threshold

Break: 0.000000e+00

--------------------------------------------------

Copying vector lines...

Rebuilding parts of topology...
Building topology ...
Registering lines: 1000 2000 3000 4000
5000 6000 7000 8000 9000
10000 11000 12000 13000 14000
15000 16000 17000 18000 19000
20000 21000 22000 23000 24000
25000 26000 27000 28000 29000
30000 31000 32000
32493 primitives registered
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 : -
Number of isles : -

--------------------------------------------------

Tool: Break lines at intersections
Intersections: 0
Intersections: 0 (line 485)
Intersections: 0 (line 984)
..... (repeats about 100 times)
Intersections: 0

--------------------------------------------------

Rebuilding topology for output vector map...
Building topology ...
Registering lines: 1000 2000 3000 4000
5000 6000 7000 8000 9000
10000 11000 12000 13000 14000
15000 16000 17000 18000 19000
20000 21000 22000 23000 24000
25000 26000 27000 28000 29000
30000 31000 32000
32493 primitives registered
Building areas:

0 areas built
0 isles built
Attaching islands:
Attaching centroids:

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
--
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2

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@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@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

3

Thanks for you reply. I think that is why it did not work. Since this is a
complete shape file, the intersections are already implemented as nodes
apparently. Both the input and the output have the same number of nodes and
they are displayed in v.digit.

I guess the v.patch/v.clean process is more for people using homegrown
shapefiles and the like.

Thanks,
R.

hamish_b wrote:

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)

--
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