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.
<p>
Application of flag <b>-t</b> enables a turntable support. 
This flag requires additional parameters <b>tlayer</b> and <b>tuclayer</b> 
that are otherwise ignored.
 The turntable allows 
to model e.g. trafic code, where some turns may be prohibited. 
This means that the input layer is expanded by 
turntable with costs of every possible turn on any possible node 
(intersection) in both directions. 
 Turntable can be created by 
 the <em><a href="v.net.html">v.net</a></em> module. 
For more information about turns in the vector network analyses see
<a href="http://grasswiki.osgeo.org/wiki/Turns_in_the_vector_network_analysis">wiki page</a>.

<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

<h3>TURNS SUPPORT</h3>

The turns support was implemnented as part of GRASS GIS turns cost project at Czech Technical University in Prague, Czech Republic.  
Eliska Kyzlikova, Stepan Turek, Lukas Bocan and Viera Bejdova participated at the project.

Implementation: Stepan Turek 
Documentation: Lukas Bocan
Mentor: Martin Landa

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