[GRASS-user] visited lines

[Moritz Lennert]

On 24/03/14 18:24, Annalisa Minelli wrote:
> Hello Moritz,
> I tried your solution and since I generated the path using the same
> v.net.path with the same -s flag (which preserves the segments) that you
> suggest, when I do the v.distance trying to "copy" the attribute cat
> from the net segments it seems not to work properly - I mean, it copies
> "something" but that "something" is wrong in the sense that it takes the
> category of the element NEAR the studied one, not 'under' even
> specifying a dmax=0..
>
> v.net.path input='gridCat' output='tmpPath2' file='tmpCoord2' -s
> v.db.droptable map='tmpPath2' -f
> v.category input='tmpPath2' output='tmpPath4a' option='del'
> v.category input='tmpPath4a' output='tmpPath2' option='add')
> v.db.addtable map='tmpPath2' columns='cat integer,tmpcat integer'
> v.distance from='tmpPath2' from_type='line' to='gridCat' to_type='line'
> upload='cat' column='tmpcat' dmax=0
>
> here a pic of my situation: http://oi62.tinypic.com/2epopcj.jpg
> in red the tmpPath2 and tmpcat value as label
> in black the gridCat and the value of the category as label

The man page says "For lines to lines, say line A to line B, v.distance 
calculates the shortest distance of each vertex in A with each segment 
(not vertex) in B. The module then calculates the shortest distance of 
each vertex in B to each segment in A. The overall shortest distance of 
A points to B segments and B points to A segments is used. Additionally, 
v.distance checks for intersections. In case of intersections, the first 
intersection found is used and the distance set to zero."

I guess that identity is not the same as intersection...
Markus ?

Moritz