NAME¶
v.net.visibility - Visibility graph construction.
KEYWORDS¶
vector, path, visibility
SYNOPSIS¶
v.net.visibility
v.net.visibility help
v.net.visibility input=
name output=
name
[
coordinate=
x,y[,
x,y,...]] [
vis=
string]
[--
overwrite] [--
verbose] [--
quiet]
Flags:¶
- --overwrite
-
Allow output files to overwrite existing files
- --verbose
-
Verbose module output
- --quiet
-
Quiet module output
Parameters:¶
- input=name
-
Name of input vector map
- output=name
-
Name for output vector map
- coordinate=x,y[,x,y,...]
-
One or more coordinates
- vis=string
-
Add points after computing the vis graph
DESCRIPTION¶
v.net.visibility computes the visibility graph of a vector map containing
lines, areas (boundaries) and points. The visibility graph is the graph where
the nodes are the end point of the lines, boundaries or simply the points.
There is an edge between two nodes if they are 'visible'. Two nodes are
visibible if there is no segments in between them, i.e. the edge doesn't
intersect any line or boundary in the vector map. This is useful to compute
the sortest path in a vector map from any two points. To do this, first you
need to compute the visibility graph and from it compute the shortest path
using
v.net.path or
d.path.
IMPORTANT : the algorithm doesn't
work well with intersecting lines (that includes overlapping)
If you compute a shortest path after computing the visibility graph you will
notice that this path might go through a vertix of a line. If this is not
wanted you might to run the map through
v.buffer first whith a small
value. Example:
v.buffer input=map output=bufferedmap buffer=1 type=point,line,area,boundary
The first argument is the input map. It supports lines, boudaries (so areas) and
points. For the algorithm to work lines and boundaries must not be
intersecting (that includes overlapping). The result map containing the
visibility graph is given in the output map. If you need to add additional
points to compute a shortest path between them afterwards you can use the
coordinate parameter.
coordinate=25556200,6686400,25556400,6686600
where 25556200,6686400 are the coordinate of the first point and
25556400,6686600 are the coordinates of the second point. Of course you can
give as many points as you want. They will be added to the visibility graph
and edges from them will be computed. You can always add those points after
computing the visibility graph. Simply use the
vis parameter. The input
will be the original vector map, the vis will be the computed visibility graph
and the output the new visibility graph which will be the vis + the new points
given with coordinate (edges will be computed as well).
v.net.visibility input=map vis=vis_map output=new_vis_map
coordinate=25556200,6686400,25556400,6686600
EXAMPLE 1¶
A simple example showing how to use the module
v.net.visibility input=lines output=graph
d.vect graph
d.vect lines col=red
EXAMPLE 2¶
An example on how to use
v.buffer with the module
v.buffer input=lines output=buffered_lines buffer=1
v.net.visibility input=buffered_lines output=graph
d.vect graph
d.vect lines col=red
EXAMPLE 3¶
An example on how to use the coordinate parameter. This will compute the
visibility graph of the vector map lines with the point 2555678,6686343
v.net.visibility input=lines output=graph coordinate=2555678,6686343
d.vect graph
d.vect lines col=red
EXAMPLE 4¶
An example on how to use the coordinate parameter with the vis parameter. Here
the vector map graph is computed then a new visibility graph is computed from
it with the point 2555678,6686343 extra
v.net.visibility input=lines output=graph
d.vect graph
d.vect lines col=red
v.net.visibility input=lines vis=graph output=new_graph
coordinate=2555678,6686343
d.erase
d.vect new_graph
d.vect lines col=red
EXAMPLE 5¶
An example for connections of points (Spearfish):
v.net.visibility input=archsites output=graph
g.region vect=archsites
d.mon x0
d.vect graph
d.vect archsites col=red
KNOWN BUGS¶
In some cases when 3 points or nodes are collinear, some wrong edges are added.
This happens only really rarly and shouldn't be a big problem. When two points
have the exact same x coordinate and are visible, some wrong edges are added.
SEE ALSO¶
d.path,
v.net,
v.net.alloc,
v.net.iso,
v.net.salesman,
v.net.steiner,
v.to.db
AUTHOR¶
Maximilian Maldacker
Mentor: Wolf Bergenheim
Last changed: $Date: 2011-11-08 10:42:51 +0100 (Tue, 08 Nov 2011) $
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© 2003-2011 GRASS Development Team