v.net.distancegrass - Online in the Cloud

PROGRAM:

NAME

v.net.distance - Computes shortest distance via the network between the given sets of
features.
Finds the shortest paths from each ’from’ point to the nearest ’to’ feature and various
information about this relation are uploaded to the attribute table.

KEYWORDS

vector, network, shortest path

SYNOPSIS

v.net.distance
v.net.distance --help
v.net.distance [-g] input=name output=name [arc_layer=string]
[arc_type=string[,string,...]] [node_layer=string] [from_layer=string]
[from_cats=range] [from_where=sql_query] [to_layer=string]
[to_type=string[,string,...]] [to_cats=range] [to_where=sql_query] [arc_column=name]
[arc_backward_column=name] [node_column=name] [--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

from_layer=string
From layer number or name
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

from_cats=range
From category values
Example: 1,3,7-9,13

from_where=sql_query
From WHERE conditions of SQL statement without ’where’ keyword
Example: income < 1000 and inhab >= 10000

to_layer=string
Layer number or name
To layer number or name
Default: 1

to_type=string[,string,...]
To feature type
Options: point, line, boundary
Default: point

to_cats=range
To category values
Example: 1,3,7-9,13

to_where=sql_query
To WHERE conditions of SQL statement without ’where’ keyword
Example: income < 1000 and inhab >= 10000

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)

DESCRIPTION

v.net.distance finds the nearest element in set to for every point in set from.

NOTES

These two sets are given by the respective layer, where and cats parameters. The type of
to features is specified by to_type parameter. All from features are points. A table is
linked to output map containing various information about the relation. More specifically,
the table has three columns: cat, tcat and dist storing category of each from feature,
category of the nearest to feature and the distance between them respectively. Furthemore,
output map contains the shorest path between each cat, tcat pair. Each path consist of
several lines. If a line is on the shorest path from a point then the category of this
point is assigned to the line. Note that every line may contain more than one category
value since a single line may be on the shortest path for more than one from feature. And
so the shortest paths can be easily obtained by querying lines with corresponding category
number.
The costs of arcs in forward and backward direction are specified by arc_column and
arc_backward_column columns respectively. If arc_backward_column is not given, the same
cost is used in both directions.

v.net.distance will not work if you are trying to find the nearest neighbors within a
group of nodes, i.e. where to and from are the same set of nodes, as the closest node will
be the node itself and the result will be zero-length paths. In order to find nearest
neighbors within a group of nodes, you can either loop through each node as to and all
other nodes as from or create a complete distance matrix with v.net.allpairs and select
the lowest non-zero distance for each node.

EXAMPLES

Shortest path and distance between school and nearest hospital
Find shortest path and distance from every school to the nearest hospital and show all
paths.

Streets are grey lines, schools are green circles, hospitals are red crosses, shortest
paths are blue lines:

# connect schools to streets as layer 2
v.net input=streets_wake points=schools_wake output=streets_net1 \
operation=connect thresh=400 arc_layer=1 node_layer=2
# connect hospitals to streets as layer 3
v.net input=streets_net1 points=hospitals output=streets_net2 \
operation=connect thresh=400 arc_layer=1 node_layer=3
# inspect the result
v.category in=streets_net2 op=report
# shortest paths from schools (points in layer 2) to nearest hospitals (points in layer 3)
v.net.distance in=streets_net2 out=schools_to_hospitals flayer=2 turn_layer=3

Distance between point source of pollution and sample points along streams
Example with streams of the NC sample data set.

# add coordinates of pollution point source of pollution as vector
pollution.txt:
634731.563206905|216390.501834892
v.in.ascii input=pollution.txt output=pollution
# add table to vector
v.db.addtable map=pollution
# add coordinates of sample points as vector
samples.txt:
634813.332814905|216333.590706166
634893.462007813|216273.763350851
634918.660011082|216254.949609689
v.in.ascii input=samples.txt output=samples
# add table to vector
v.db.addtable map=samples
# connect samples and pollution to streams
v.net -c input=streams points=samples output=streams_samples \
operation=connect node_layer=3 threshold=10 \
v.net -c input=streams_samples points=pollution
output=streams_samples_pollution operation=connect \
node_layer=4 threshold=10
# check vector layers
v.category input=streams_samples_pollution option=report
Layer/table: 1/streams_samples_pollution
type count min max
point 0 0 0
line 8562 40102 101351
boundary 0 0 0
centroid 0 0 0
area 0 0 0
face 0 0 0
kernel 0 0 0
all 8562 40102 101351
Layer: 3
type count min max
point 3 1 3
line 0 0 0
boundary 0 0 0
centroid 0 0 0
area 0 0 0
face 0 0 0
kernel 0 0 0
all 3 1 3
Layer: 4
type count min max
point 1 1 1
line 0 0 0
boundary 0 0 0
centroid 0 0 0
area 0 0 0
face 0 0 0
kernel 0 0 0
all 1 1 1
# calculate distance between sample points and pollution point source
v.net.distance input=streams_samples_pollution \
output=distance_samples_to_pollution from_layer=3 to_layer=4
# check results
v.report map=distance_samples_to_pollution@vnettest option=length
cat|tcat|dist|length
1|1|100.0|100.0
2|1|200.0|200.0
3|1|231.446|231.446

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