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

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.

AUTHOR

       Maximilian Maldacker
       Mentor: Wolf Bergenheim

       Last changed: $Date: 2013-05-23 13:01:55 -0700 (Thu, 23 May 2013) $

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