xenial (1) v.net.distance.1grass.gz

Provided by: grass-doc_7.0.3-1build1_all bug

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

SEE ALSO

        v.net.path, v.net.allpairs, v.net.distance, v.net.alloc

AUTHORS

       Daniel Bundala, Google Summer of Code 2009, Student
       Wolf Bergenheim, Mentor
       Markus Metz

       Last changed: $Date: 2015-12-14 13:56:17 +0100 (Mon, 14 Dec 2015) $

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