1v.net.path(1) GRASS GIS User's Manual v.net.path(1)
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6 v.net.path - Finds shortest path on vector network.
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9 vector, network, shortest path
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12 v.net.path
13 v.net.path --help
14 v.net.path [-tgs] input=name output=name arc_layer=string
15 arc_type=string[,string,...] node_layer=string [file=name] [arc_col‐
16 umn=string] [arc_backward_column=string] [node_column=string]
17 [dmax=float] [turn_layer=string] [turn_cat_layer=string] [--over‐
18 write] [--help] [--verbose] [--quiet] [--ui]
19 Flags:
21 -t
22 Use turntable
23 -g
25 Use geodesic calculation for longitude-latitude locations
26 -s
28 Write output as original input segments, not each path as one line.
29 --overwrite
31 Allow output files to overwrite existing files
32 --help
34 Print usage summary
35 --verbose
37 Verbose module output
38 --quiet
40 Quiet module output
41 --ui
43 Force launching GUI dialog
44 Parameters:
46 input=name [required]
47 Name of input vector map
48 Or data source for direct OGR access
49 output=name [required]
51 Name for output vector map
52 arc_layer=string [required]
54 Arc layer
55 Vector features can have category values in different layers. This
56 number determines which layer to use. When used with direct OGR
57 access this is the layer name.
58 Default: 1
59 arc_type=string[,string,...]Â [required]
61 Arc type
62 Input feature type
63 Options: line, boundary
64 Default: line,boundary
65 node_layer=string [required]
67 Node layer
68 Vector features can have category values in different layers. This
69 number determines which layer to use. When used with direct OGR
70 access this is the layer name.
71 Default: 2
72 file=name
74 Name of file containing start and end points. If not given, read
75 from stdin
76 arc_column=string
78 Arc forward/both direction(s) cost column (number)
79 arc_backward_column=string
81 Arc backward direction cost column (number)
82 node_column=string
84 Node cost column (number)
85 dmax=float
87 Maximum distance to the network
88 If start/end are given as coordinates. If start/end point is out‐
89 side this threshold, the path is not found and error message is
90 printed. To speed up the process, keep this value as low as possi‐
91 ble.
92 Default: 1000
93 turn_layer=string
95 Layer with turntable
96 Relevant only with -t flag
97 Default: 3
98 turn_cat_layer=string
100 Layer with unique categories used in turntable
101 Relevant only with -t flag
102 Default: 4
103
105 v.net.path determines least costly, e.g. shortest or fastest path(s) on
106 a vector network.
107 Costs may be either line lengths, or attributes saved in a database ta‐
109 ble. These attribute values are taken as costs of whole segments, not
110 as costs to traverse a length unit (e.g. meter) of the segment. For
111 example, if the speed limit is 100 km / h, the cost to traverse a 10 km
112 long road segment must be calculated as
113 length / speed = 10 km / (100 km/h) = 0.1 h.
114 Supported are cost assignments for both arcs and nodes, and also dif‐
115 ferent costs for both directions of a vector line. For areas, costs
116 will be calculated along boundary lines.
117 The input vector needs to be prepared with v.net operation=connect in
119 order to connect points representing center nodes to the network.
120 Nodes and arcs can be closed using cost = -1.
122 Least cost paths are written to the output vector map with an attached
124 attribute table.
125 Nodes can be
127 · piped into the program from file or from stdin, or
129 · defined in the graphical user interface ("enter values interac‐
131 tively").
132 The syntax is as follows:
133 id start_point_category end_point_category
134 (Example: 1 1 2)
135 or
137 id start_point_x start_point_y end_point_x end_point_y
138 Points specified by category must be exactly on network nodes, and the
140 input vector map needs to be prepared with v.net operation=connect.
141 When specifying coordinates, the next network node to a given coordi‐
143 nate pair is used.
144 The attribute table will contain the following attributes:
146 · cat - path unique category assigned by module
148 · id - path id (read from input)
150 · fcat - from point category
152 · tcat - to point category
154 · sp - result status:
156 · 0 - OK, path found
158 · 1 - node is not reachable
160 · 2 - point of given category does not exist
162 · cost - travelling costs (on the network, not to/from network)
164 · fdist - the distance from first point to the network
166 · tdist - the distance from the network to second point
168 Application of flag -t enables a turntable support. This flag requires
170 additional parameters turn_layer and turn_cat_layer that are otherwise
171 ignored. The turntable allows to model e.g. traffic code, where some
172 turns may be prohibited. This means that the input layer is expanded
173 by turntable with costs of every possible turn on any possible node
174 (intersection) in both directions. Turntable can be created by the
175 v.net module. For more information about turns in the vector network
176 analyses see wiki page.
177
179 Nodes and arcs can be closed using cost = -1.
180 If the cost columns arc_column, arc_backward_column and node_column are
182 not specified, the length of network segments is measured and zero
183 costs are assumed for nodes.
184 When using attributes, the length of segments is not used. To get accu‐
186 rate results, the line length must be taken into account when assigning
187 costs as attributes. For example, to get the fastest path, the columns
188 ’max_speed’ and ’length’ are required. The correct fastest path can
189 then be found by specifying arc_column=length/max_speed. If not yet
190 existing, the column containing the line length ("length") has to added
191 to the attributes table using v.to.db.
192
194 Shortest (red) and fastest (blue) path between two digitized nodes
195 (Spearfish):
196 # Spearfish
198 echo "1|601955.1|4916944.9|start
199 2|594385.6|4921565.2|end" | v.in.ascii in=- cat=1 x=2 y=3 out=startend col="cat integer, \
200 east double precision, north double precision, label varchar(6)"
201 v.db.select startend
202 g.copy vect=roads,myroads
203 # create lines map connecting points to network
204 v.net myroads points=startend out=myroads_net op=connect thresh=500 arc_layer=1 node_layer=2
205 # set up costs
206 # create unique categories for each road in layer 3
207 v.category in=myroads_net out=myroads_net_time opt=add cat=1 layer=3 type=line
208 # add new table for layer 3
209 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"
210 # copy road type to layer 3
211 v.to.db myroads_net_time layer=3 qlayer=1 opt=query qcolumn=label columns=label
212 # upload road length in miles
213 v.to.db myroads_net_time layer=3 type=line option=length col=length unit=miles
214 # set speed limits in miles / hour
215 v.db.update myroads_net_time layer=3 col=speed val="5.0"
216 v.db.update myroads_net_time layer=3 col=speed val="75.0" where="label=’interstate’"
217 v.db.update myroads_net_time layer=3 col=speed val="75.0" where="label=’primary highway, hard surface’"
218 v.db.update myroads_net_time layer=3 col=speed val="50.0" where="label=’secondary highway, hard surface’"
219 v.db.update myroads_net_time layer=3 col=speed val="25.0" where="label=’light-duty road, improved surface’"
220 v.db.update myroads_net_time layer=3 col=speed val="5.0" where="label=’unimproved road’"
221 # define traveling costs as traveling time in minutes:
222 # set forward costs
223 v.db.update myroads_net_time layer=3 col=cost val="length / speed * 60"
224 # set backward costs
225 v.db.update myroads_net_time layer=3 col=bcost val="length / speed * 60"
226 # ... the ’start’ and ’end’ nodes have category number 1 and 2
227 # Shortest path: ID as first number, then cat1 and cat2
228 echo "1 1 2" | v.net.path myroads_net_time arc_layer=3 node_layer=2 out=mypath
229 # Fastest path: ID as first number, then cat1 and cat2
230 echo "1 1 2" | v.net.path myroads_net_time arc_layer=3 node_layer=2 arc_column=cost arc_backward_column=bcost out=mypath_time
231 To display the result, run for example:
232 g.region vector=myroads_net
233 d.mon x0
234 d.vect myroads_net
235 # show shortest path
236 d.vect mypath col=red width=2
237 # show fastest path
238 d.vect mypath_time col=blue width=2
239 # start and end point
240 d.vect myroads_net icon=basic/triangle fcol=green size=12 layer=2
241 d.font font=Vera
242 d.vect startend disp=cat type=point lsize=14 layer=2
243
245 d.path, v.net, v.net.alloc, v.net.iso, v.net.salesman, v.net.steiner,
246 v.to.db
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249 Radim Blazek, ITC-Irst, Trento, Italy
250 Documentation: Markus Neteler, Markus Metz
251 TURNS SUPPORT
253 The turns support was implemnented as part of GRASS GIS turns cost
254 project at Czech Technical University in Prague, Czech Republic.
255 Implementation: Stepan Turek
257 Documentation: Lukas Bocan, Eliska Kyzlikova, Viera Bejdova
258 Mentor: Martin Landa
259
261 Available at: v.net.path source code (history)
262 Main index | Vector index | Topics index | Keywords index | Graphical
264 index | Full index
265 © 2003-2020 GRASS Development Team, GRASS GIS 7.8.5 Reference Manual
267GRASS 7.8.5 v.net.path(1)