[GRASS-user] problem with v.clean and intersection pts

hardinej hardinej at gmail.com
Wed May 13 21:36:53 EDT 2009

Hi everyone,
Thanks in advance.
I'm trying to extract intersection points. I have a shoreline I extracted
using r.contour and many lines that cross the shoreline that are the output
of v.distance.
I want the intersection points so I'm patching the shoreline and crossbars
and then using v.clean tool=break err=intersections. V.clean only gives me
one intersection which is where the shoreline reaches the edge of the
region, none in the actual intersections. 
Now I'll give some extra information in case it helps:
The workflow that I'm using is:
#digitize line roughly parallel to shoreline
v.digit map=ShorelineMeasLine -n bgcmd="d.rast R_slope; d.vect
R_maximum_036m; d.vect R_minimum_036m" --o
v.to.points -vi input=ShorelineMeasLine out=ShorelineMeasPts dmax=50
type=line --o
#move vector line to the other side of shoreline
v.digit map=ShorelineMeasLine -n bgcmd="d.rast R_slope; d.vect
R_maximum_036m; d.vect R_minimum_036m"
#make the crossbars
v.distance -p from=ShorelineMeasPts to=ShorelineMeasLine from_type=point
to_type=line from_layer=2 upload=dist column=1 output=ShorelineMeasPerpLines
v.patch input=R_20080327_75m,ShorelineMeasPerpLines
output=R_20080327_75m_WPerps --o
#find intersections
v.clean input=R_20080327_75m_WPerps output=R_20080327_75m_WPerps_break
error=R_20080327_75m_Pts tool=break --o
I don't know if this helps, but if I query one of the crossbars (v.distance
output), I get:
East: 930243.068465
North: 209846.058091

Map: ShorelineMeasPerpLines 
Mapset: rodanthe
Type: Line
Line: 85
Length: 215.661245
And if I query the shoreline, I get:
East: 930135.548755
North: 209954.759336

Map: R_20080327_75m 
Mapset: rodanthe
Type: Line
Line: 1
Length: 10750.507559
Line height: 0.750000
Layer: 1
Category: 1 

Driver: dbf
Database: /home/eric/obx/rodanthe/dbf/
Table: R_20080327_75m
Key column: cat
cat : 1
level : 0.75

I hope I was clear and gave enough information.
Thanks a lot,

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