Geografic-Information-System/vector/v.net.alloc/v.net.alloc.html

<h2>DESCRIPTION</h2>

<em>v.net.alloc</em> allocates subnets for nearest centers 
(direction from center). center nodes must be opened (costs &gt;= 0).
Costs of center nodes are used in the calculation. 
<p>
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
<br>
length / speed = 10 km / (100 km/h) = 0.1 h.
<br>
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.
<p>
The input vector needs to be prepared with <em>v.net operation=connect</em> 
in order to connect points representing center nodes to the network.

<h2>NOTES</h2>

Nodes and arcs can be closed using cost = -1. 
<p>
Center nodes can also be assigned to vector nodes using 
<em><a href="wxGUI.vdigit.html">wxGUI vector digitizer</a></em>. 

<h2>EXAMPLES</h2>

<p>1. Subnetwork allocation using distance:
<p><img src="v_net_alloc.png" alt="v.net.alloc example using distance" border="1">
<br>
<p>2. Subnetwork allocation using traveling time:
<p><img src="v_net_alloc_time.png" alt="v.net.alloc example using time" border="1">
<br>

<p>Example 1: <em>Calculating subnets for 3 center nodes using distances</em>
<div class="code"><pre>
# 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 ccats=1-100000 nlayer=2

# report categories
v.category myroads_net_alloc option=report
</pre></div>

To display the result, run for example:

<div class="code"><pre>
# show result
g.region vect=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
</pre></div>

<p>Example 2: <em>Calculating subnets for 3 center nodes using traveling time</em><br>

<div class="code"><pre>
# 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 alayer=1 nlayer=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 alayer=3 nlayer=2 afcol=cost abcol=bcost out=myroads_net_alloc_time ccats=1-3
</pre></div>

To display the result, run for example:

<div class="code"><pre>
# show result
g.region vect=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
</pre></div>

<h2>SEE ALSO</h2>

<em><a href="d.path.html">d.path</a></em>,
<em><a href="v.net.html">v.net</a></em>,
<em><a href="v.net.iso.html">v.net.iso</a></em>,
<em><a href="v.net.path.html">v.net.path</a></em>,
<em><a href="v.net.steiner.html">v.net.steiner</a></em>,
<em><a href="v.net.salesman.html">v.net.salesman</a></em>

<h2>AUTHOR</h2>

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


<p><i>Last changed: $Date$</i>