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v.net.visibility(1grass) | Grass User's Manual | v.net.visibility(1grass) |
NAME¶
v.net.visibility - Visibility graph construction.KEYWORDS¶
vector, path, visibilitySYNOPSIS¶
v.net.visibilityFlags:¶
- --overwrite
-
- --verbose
-
- --quiet
-
Parameters:¶
- input=name
-
- output=name
-
- coordinate=x,y[,x,y,...]
-
- vis=string
-
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 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)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:coordinate=25556200,6686400,25556400,6686600
EXAMPLES¶
Example 1¶
A simple example (North Carolina sample data) showing how to use the module:Example 2d.er¶
An example on how to use v.buffer along with the module: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: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:coordinate=669547.97,208348.20
Example 5¶
An example for connections of points (Spearfish):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.dbAUTHOR¶
Maximilian MaldackerGRASS 6.4.4 |