In terms of network analysis, a network consists of nodes connected by arcs. In a vector map prepared for network analysis, nodes are represented by the grass-internal geometry type node and arcs by the geometry type line. If a line consists of several vertices and segments (the typical case), only its starting and ending vertex are regarded as network nodes. Further more, explicit starting and ending nodes for e.g. least cost path search or subnetwork allocation are represented by the geometry type point which must be identical with the start or end vertex (network node) of a line.
In general, network analysis will find the least costly (shortest or fastest) path from point A to point B by follwing the existing lines. This implies that the points A, B must lie at the start or end point of a line with is part of the network. If no line is starting or ending at a given point, this point is not part of the network, i.e. the point is unconnected and unreachable.
Create nodes globally for all line ends and intersections:
v.net input=roads output=roads_node operation=nodes
Merge in nodes from a separate map within given threshold:
echo "1|601955.1|4916944.9|start
2|594385.6|4921565.2|end" | v.in.ascii in=- cat=1 x=2 y=3 out=startend col="cat integer, \
east double precision, north double precision, label varchar(6)"
#create lines map connecting points to network (on layer 2)
v.net myroads points=startend out=myroads_net op=connect thresh=200
Last changed: $Date$