Ubuntu Manpage: v.net.visibility - Performs visibility graph construction.

Provided by: grass-doc_7.0.3-1build1_all

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

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 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)

NOTES

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 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, 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

EXAMPLES

   Example 1
       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

   Example 2
       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

   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 coordinates=2555678,6686343
       d.vect graph
       d.vect lines col=red

   Example 4
       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

   Example 5
       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

KNOWN ISSUES

       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.

AUTHOR

       Maximilian Maldacker
       Mentor: Wolf Bergenheim

       Last changed: $Date: 2015-05-11 02:16:13 +0200 (Mon, 11 May 2015) $

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       © 2003-2016 GRASS Development Team, GRASS GIS 7.0.3 Reference Manual

GRASS 7.0.3                                                                             v.net.visibility(1grass)