DESCRIPTION

v.net.allpairs computes the shortest path between each selected node and all other selected nodes.

If the input vector has been prepared with v.net and v.net.allpairs should use cost columns, further preparation is of the input vector required. In contrast to the output of v.net and the behaviour of other v.net.* modules, v.net.allpairs uses the same layer to read cost columns for arcs and to read node categories. Therefore new, unique categories for points must be added to the layer with cost columns for lines with v.category.
If abcolumn is not given then then the same costs are used for forward and backward arcs.

NOTES

An attribute table is created and linked to layer 1. The table contains three columns: cat, to_cat, cost. Each entry denotes the cost of the shortest path from cat to to_cat. If the cost is negative then no path exists. If points are specified by cats, layer or where parameters then the table is filled only for the selected points.
If the -a flag is set then new points are added on nodes without nodes. These points have the largest category. Precisely, the category value of each new point is larger than any of the old categories. Note that these new points are not included in the output table.

EXAMPLE

Find shortest path along roads from selected archsites (Spearfish sample dataset): 
# prepare network: connect archsites to roads with threshold 200
v.net input=roads@PERMANENT points=archsites@PERMANENT \
output=roads_net operation=connect thresh=200

# verify result
v.category input=roads_net option=report

# only lines should have a category in layer 1
# only points should have a category in layer 2

# shortest path between all points with categories 1 - 5 in layer 2
v.net.allpairs input=roads_net layer=2 cats=1-5 out=roads_net_all
v.db.select roads_net_all
Result in matrix form: 
from\to	1		3		4		5
1	0		18820.386	17206.651	17373.274
3	18820.386	0		1739.079	9040.575
4	17206.651	1739.079	0		7426.84
5	17373.274	9040.575	7426.84		0

SEE ALSO

v.net.path, v.net.distance

AUTHORS

Daniel Bundala, Google Summer of Code 2009, Student
Wolf Bergenheim, Mentor
Markus Metz

Last changed: $Date$