## DESCRIPTION

v.net.alloc allocates subnets for nearest centers (direction from center). center nodes must be opened (costs >= 0). Costs of center nodes are used in the calculation.

Costs may be either line lengths, or attributes saved in a database table. These attribute values are taken as costs of whole segments, not as costs to traverse a length unit (e.g. meter) of the segment. For example, if the speed limit is 100 km / h, the cost to traverse a 10 km long road segment must be calculated as
length / speed = 10 km / (100 km/h) = 0.1 h.
Supported are cost assignments for both arcs and nodes, and also different costs for both directions of a vector line. For areas, costs will be calculated along boundary lines.

The input vector needs to be prepared with v.net operation=connect in order to connect points representing center nodes to the network.

## NOTES

Nodes and arcs can be closed using cost = -1.

Center nodes can also be assigned to vector nodes using wxGUI vector digitizer.

## EXAMPLES

1. Subnetwork allocation using distance:

2. Subnetwork allocation using traveling time:

Example 1: Calculating subnets for 3 center nodes using distances

    # Spearfish

    # center nodes:
    echo "591235.5|4926306.62|1
    596591.8|4917042.5|2
    602722.9|4923544.2|3" | v.in.ascii in=- out=centernodes

    g.copy vect=roads,myroads

    # connect points to network
    v.net myroads points=centernodes out=myroads_net op=connect thresh=200

    # allocate, specifying range of center cats (easier to catch all):
    v.net.alloc myroads_net out=myroads_net_alloc center_cats=1-100000 node_layer=2

    # report categories
    v.category myroads_net_alloc option=report

To display the result, run for example:

    # show result
    g.region vector=myroads_net
    d.mon x0
    d.vect myroads_net layer=1

    # the result has to be selected by category number of the relevant node:
    d.vect myroads_net_alloc cat=1 col=red layer=1
    d.vect myroads_net_alloc cat=2 col=green layer=1
    d.vect myroads_net_alloc cat=3 col=yellow layer=1

    # center nodes
    d.vect myroads_net col=red icon=basic/triangle fcol=green size=12 layer=2

Example 2: Calculating subnets for 3 center nodes using traveling time

    # Spearfish

    # center nodes:
    echo "591235.5|4926306.62|1
    596591.8|4917042.5|2
    602722.9|4923544.2|3" | v.in.ascii in=- out=centernodes

    g.copy vect=roads,myroads

    # create lines map connecting points to network
    v.net myroads points=centernodes out=myroads_net op=connect thresh=500 arc_layer=1 node_layer=2

    # set up costs

    # create unique categories for each road in layer 3
    v.category in=myroads_net out=myroads_net_time opt=add cat=1 layer=3 type=line

    # add new table for layer 3
    v.db.addtable myroads_net_time layer=3 col="cat integer,label varchar(43),length double precision,speed double precision,cost double precision,bcost double precision"

    # copy road type to layer 3
    v.to.db myroads_net_time layer=3 qlayer=1 opt=query qcolumn=label columns=label

    # upload road length in miles
    v.to.db myroads_net_time layer=3 type=line option=length col=length unit=miles

    # set speed limits in miles / hour
    v.db.update myroads_net_time layer=3 col=speed val="5.0"
    v.db.update myroads_net_time layer=3 col=speed val="75.0" where="label='interstate'"
    v.db.update myroads_net_time layer=3 col=speed val="75.0" where="label='primary highway, hard surface'"
    v.db.update myroads_net_time layer=3 col=speed val="50.0" where="label='secondary highway, hard surface'"
    v.db.update myroads_net_time layer=3 col=speed val="25.0" where="label='light-duty road, improved surface'"
    v.db.update myroads_net_time layer=3 col=speed val="5.0" where="label='unimproved road'"

    # define traveling costs as traveling time in minutes:

    # set forward costs
    v.db.update myroads_net_time layer=3 col=cost val="length / speed * 60"
    # set backward costs
    v.db.update myroads_net_time layer=3 col=bcost val="length / speed * 60"

    # subnetwork allocation with fastest paths
    v.net.alloc in=myroads_net_time arc_layer=3 node_layer=2 arc_column=cost arc_backward_column=bcost out=myroads_net_alloc_time center_cats=1-3

To display the result, run for example:

    # show result
    g.region vector=myroads_net
    d.mon x0
    d.vect myroads_net type=line layer=1

    # the result has to be selected by category number of the relevant node:
    d.vect myroads_net_alloc_time cat=1 col=red layer=1
    d.vect myroads_net_alloc_time cat=2 col=green layer=1
    d.vect myroads_net_alloc_time cat=3 col=yellow layer=1

    # center nodes
    d.vect myroads_net_time col=red icon=basic/triangle fcol=green size=12 type=point layer=2

## SEE ALSO

d.path, v.net, v.net.iso, v.net.path, v.net.steiner, v.net.salesman

## AUTHOR

Radim Blazek, ITC-Irst, Trento, Italy
Documentation: Markus Neteler, Markus Metz

Last changed: $Date: 2014-12-24 15:44:33 +0100 (Wed, 24 Dec 2014) $