GRASS GIS manual: v.net.iso

Note: A new GRASS GIS stable version has been released: GRASS GIS 7.4, available here.
Updated manual page: here

NAME

v.net.iso - Splits net by cost isolines.
Splits net to bands between cost isolines (direction from center). Center node must be opened (costs >= 0). Costs of center node are used in calculation.

KEYWORDS

vector, network, isolines

SYNOPSIS

v.net.iso

v.net.iso --help

v.net.iso [-g] input=name output=name [arc_layer=string] [arc_type=string[,string,...]] [node_layer=string] [arc_column=name] [arc_backward_column=name] [node_column=name] center_cats=range costs=integer[,integer,...] [--overwrite] [--help] [--verbose] [--quiet] [--ui]

Flags:

-g: Use geodesic calculation for longitude-latitude locations
--overwrite: Allow output files to overwrite existing files
--help: Print usage summary
--verbose: Verbose module output
--quiet: Quiet module output
--ui: Force launching GUI dialog

Parameters:

input=name [required]: Name of input vector map; Or data source for direct OGR access
output=name [required]: Name for output vector map
arc_layer=string: Arc layer; Vector features can have category values in different layers. This number determines which layer to use. When used with direct OGR access this is the layer name.; Default: 1
arc_type=string[,string,...]: Arc type; Input feature type; Options: line, boundary; Default: line,boundary
node_layer=string: Node layer; Vector features can have category values in different layers. This number determines which layer to use. When used with direct OGR access this is the layer name.; Default: 2
arc_column=name: Arc forward/both direction(s) cost column (number)
arc_backward_column=name: Arc backward direction cost column (number)
node_column=name: Node cost column (number)
center_cats=range [required]: Category values; Categories of centers (points on nodes) to which net will be allocated, layer for this categories is given by nlayer option
costs=integer[,integer,...] [required]: Costs for isolines

DESCRIPTION
NOTES
EXAMPLES
SEE ALSO
AUTHOR

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:

v.net.iso example with distance

Isonetwork using time:

v.net.iso example with traveling 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 center_cats=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 arc_layer=3 node_layer=2 arc_column=cost arc_backward_column=bcost center_cats=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

AUTHOR

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

Last changed: $Date: 2014-12-24 06:44:33 -0800 (Wed, 24 Dec 2014) $

SOURCE CODE

Available at: v.net.iso source code (history)