Note: A new GRASS GIS stable version has been released: GRASS GIS 7.4, available here.
Updated manual page: here
NAME
v.net.visibility - Performs visibility graph construction.
KEYWORDS
vector,
network,
shortest path,
visibility
SYNOPSIS
v.net.visibility
v.net.visibility --help
v.net.visibility input=name output=name [coordinates=east,north] [visibility=name] [--overwrite] [--help] [--verbose] [--quiet] [--ui]
Flags:
- --overwrite
- Allow output files to overwrite existing files
- --help
- Print usage summary
- --verbose
- Verbose module output
- --quiet
- Quiet module output
- --ui
- Force launching GUI dialog
Parameters:
- input=name [required]
- Name of input vector map
- Or data source for direct OGR access
- output=name [required]
- Name for output vector map
- coordinates=east,north
- Coordinates
- visibility=name
- Name of input vector map containing visable points
- Add points after computing the visibility graph
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 points. There is an edge between two nodes if they
are 'visible' to each other. Two nodes are visibible if there are no segments
in between of them, i.e. the edge does not intersect any line or boundary
in the vector map. This is useful to compute the shortest path in a
vector map from any two points. To do this, first you need to compute
the visibility graph and from that to 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 vertex of a line. If
this is not what you wanted you might need to process the map
in
v.buffer, initially with 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, boundaries
(so, areas) and points. For the algorithm was written to work with lines
and boundaries not intersecting each other (that includes overlapping).
The resulting 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 coordinates parameter, e.g.:
coordinates=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 need. 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
visibility 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 visibility=vis_map output=new_vis_map \
coordinates=25556200,6686400,25556400,6686600
A simple example (North Carolina sample data) showing how to use the module:
v.extract input=zipcodes_wake output=areas_7_11_25 cats=7,11,25
g.region vector=zipcodes_wake
d.mon wx0
d.vect areas_7_11_25
v.net.visibility input=areas_7_11_25 output=graph
d.vect graph
d.vect areas_7_11_25 color=red type=boundary
An example on how to use
v.buffer
along 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
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 coordinates=2555678,6686343
d.vect graph
d.vect lines col=red
An example (North Carolina sample data) 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 669547.97,208348.20 extra:
v.extract input=zipcodes_wake output=areas_7_11_25 cats=7,11,25
g.region vector=zipcodes_wake
d.mon wx0
d.vect areas_7_11_25
v.net.visibility input=zipcodes_wake output=graph
v.net.visibility input=zipcodes_wake visibility=graph output=new_graph \
coordinates=669547.97,208348.20
d.erase
d.vect areas_7_11_25
echo "symbol basic/star 20 669547.97 208348.20 black red" | d.graph -m
d.vect new_graph
d.vect areas_7_11_25 color=red type=boundary
An example for connections of points (Spearfish):
v.net.visibility input=archsites output=graph
g.region vector=archsites
d.mon wx0
d.vect graph
d.vect archsites col=red
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.
d.path,
v.net,
v.net.alloc,
v.net.iso,
v.net.salesman,
v.net.steiner,
v.to.db
Maximilian Maldacker
Mentor: Wolf Bergenheim
Last changed: $Date: 2016-08-30 06:30:47 -0700 (Tue, 30 Aug 2016) $
SOURCE CODE
Available at: v.net.visibility source code (history)
Note: A new GRASS GIS stable version has been released: GRASS GIS 7.4, available here.
Updated manual page: here
Main index |
Vector index |
Topics index |
Keywords index |
Full index
© 2003-2018
GRASS Development Team,
GRASS GIS 7.0.7svn Reference Manual