v.net.visibility (1)

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 visible 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 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

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=areas_7_11_25 output=graph

v.net.visibility input=areas_7_11_25 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

Example 6

Here is an example with artificial data.

Load data using here document syntax (Bash and unix-like commands lines only):

v.in.ascii input=- output=simple format=standard <

VERTI:

B 6

82.19908257 75.21788991

81.67889908 71.40321101

83.58623853 71.72522936

84.3293578 75.21788991

82.24862385 76.06009174

82.19908257 75.21788991

C 1 1

82.88897401 73.66318782

1 1

C 1 1

90.72645705 75.61248675

1 2

C 1 1

89.37944702 69.51012912

1 3

C 1 1

81.60108979 67.78669725

1 4

B 5

89.92752294 73.95458716

92.37981651 75.11880734

91.56238532 77.29862385

88.96146789 75.88669725

89.92752294 73.95458716

B 10

88.54036697 70.70963303

87.92192518 70.04087417

87.89633028 69.00045872

88.66460807 68.13372867

90.15108904 68.23290821

90.9426344 68.97588202

90.86880734 70.11513761

90.00144697 70.78336312

89.06055046 70.95733945

88.54036697 70.70963303

B 9

78.73119266 71.35366972

80.76238532 68.90137615

84.20550459 66.91972477

89.87798165 65.35917431

83.23494031 66.27685175

80.34278748 68.00837238

78.38484005 71.40292009

78.40917431 72.27018349

78.73119266 71.35366972

EOF

Compute the graph:

v.net.visibility input=simple output=graph

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.

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: 2016-12-11 19:59:46 +0100 (Sun, 11 Dec 2016) $

SOURCE CODE

Available at: v.net.visibility source code (history)

Main index | Vector index | Topics index | Keywords index | Graphical index | Full index

2003-2017 GRASS Development Team, GRASS GIS 7.2.1 Reference Manual

GRASS 7.2.1 v.net.visibility(1grass)