v.net.iso(1)

NAME
v.net.iso

DESCRIPTION
v.net.iso splits a network into bands between cost isolines (distance from center). Center nodes must be opened (costs >= 0). The 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.

Nodes must be on the isolines.

EXAMPLES
The map must contain at least one center (point) on the vector network which can be patched into with v.net.

Isonetwork using distance:

Isonetwork using time:

  Subdivision of a network using distance:
# Spearfish
# start node:
echo "591280.5|4926396.0|1" | v.in.ascii in=- out=startnode
g.copy vect=roads,myroads
# connect point to network
v.net myroads points=startnode out=myroads_net op=connect thresh=200
# define iso networks using distance:
v.net.iso input=myroads_net output=myroads_net_iso ccats=1-100000 costs=1000,2000,5000
The network is divided into 4 categories:
v.category myroads_net_iso option=report
# ... reports 4 categories:
#cat | distance from point in meters
#1 0 - < 1000
#2 1000 - < 2000
#3 2000 - < 5000
#4 >= 5000
To display the result, run for example:
g.region n=4928200 s=4922300 w=589200 e=596500
d.mon x0
d.vect myroads_net_iso col=blue cats=1
d.vect myroads_net_iso col=green cats=2
d.vect myroads_net_iso col=orange cats=3
d.vect myroads_net_iso col=magenta cats=4
d.vect myroads_net col=red icon=basic/triangle fcol=green size=12 layer=2

  Subdivision of a network using traveling time:
Prepare the network as above:
# Spearfish
# start node:
echo "591280.5|4926396.0|1" | v.in.ascii in=- out=startnode
g.copy vect=roads,myroads
# connect point to network
v.net myroads points=startnode out=myroads_net op=connect thresh=200
Define costs as traveling time dependent on speed limits:
# 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"
# define iso networks using traveling time:
v.net.iso input=myroads_net_time output=myroads_net_iso_time alayer=3 nlayer=2 afcol=cost abcol=bcost ccats=1-100000 costs=1,2,5
To display the result, run for example:
# add table with labels and coloring
v.db.addtable myroads_net_iso_time columns="cat integer,trav_time varchar(20),GRASSRGB varchar(11)"
# labels
v.db.update map=myroads_net_iso_time layer=1 column=trav_time value="0 - 1" where="cat = 1"
v.db.update map=myroads_net_iso_time layer=1 column=trav_time value="1 - 2" where="cat = 2"
v.db.update map=myroads_net_iso_time layer=1 column=trav_time value="2 - 5" where="cat = 3"
v.db.update map=myroads_net_iso_time layer=1 column=trav_time value="> 5" where="cat = 4"
# colors
# cats=1: blue
v.db.update map=myroads_net_iso_time layer=1 column=GRASSRGB value="000:000:255" where="cat = 1"
# cats=2: green
v.db.update map=myroads_net_iso_time layer=1 column=GRASSRGB value="000:255:000" where="cat = 2"
# cats=3: orange
v.db.update map=myroads_net_iso_time layer=1 column=GRASSRGB value="255:128:000" where="cat = 3"
# cats=4: magenta
v.db.update map=myroads_net_iso_time layer=1 column=GRASSRGB value="255:000:255" where="cat = 4"
# show results
g.region n=4928200 s=4922300 w=589200 e=596500
d.mon x0
d.vect myroads_net_iso_time layer=1 -a rgb_col=GRASSRGB
d.vect myroads_net col=red icon=basic/triangle fcol=green size=12 layer=2

SEE ALSO
d.path, v.net, v.net.alloc, v.net.path, v.net.salesman, v.net.steiner, v.patch

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

Last changed: $Date: 2011-11-08 10:42:51 +0100 (Tue, 08 Nov 2011) $

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