1v.segment(1) GRASS GIS User's Manual v.segment(1)
2
6 v.segment - Creates points/segments from input vector lines and posi‐
7 tions.
8
10 vector, geometry, node, point, segment, vertex
11
13 v.segment
14 v.segment --help
15 v.segment input=name [layer=string] output=name [rules=name]
16 [--overwrite] [--help] [--verbose] [--quiet] [--ui]
17 Flags:
19 --overwrite
20 Allow output files to overwrite existing files
21 --help
23 Print usage summary
24 --verbose
26 Verbose module output
27 --quiet
29 Quiet module output
30 --ui
32 Force launching GUI dialog
33 Parameters:
35 input=name [required]
36 Name of input vector lines map
37 Or data source for direct OGR access
38 layer=string
40 Layer number or name
41 Vector features can have category values in different layers. This
42 number determines which layer to use. When used with direct OGR
43 access this is the layer name.
44 Default: 1
45 output=name [required]
47 Name for output vector map
48 rules=name
50 Name of file containing segment rules
51 ’-’ for standard input
52
54 v.segment generates segments or points from input lines and from posi‐
55 tions read from a text file or ’stdin’. It includes the creation of
56 parallel lines or points in given destination from the line.
57 The format is:
59 P <point id> <line cat> <offset> [<side offset>]
60 L <segment id> <line cat> <start offset> <end offset> [<side offset>]
61 The offsets can be percent values of the line length. If the offsets
62 are negative, they start from the end node of the line. -0 means the
63 end of the line.
64 The user could send to stdin something like:
66 P 1 356 24.56
67 P 2 495 12.31
68 P 3 500 -12.31
69 P 4 510 -20%
70 ...
71 (pipe or redirect from file into the command).
72
74 A segment is only created for the first line found of the specified
75 category.
76 Points are generated along the lines at the given distance(s) or per‐
78 cent(s) of the line length from the beginning or end, if offsets are
79 negative, of the vector line.
80 The side offset is the orthogonal distance from the line. Positive side
82 offsets are to the right side of the line going forward, negative off‐
83 sets are to the left (d.vect with display=shape,dir shows the direction
84 of vector lines). As the segment distance is measured along the origi‐
85 nal line, side-offset lines will be longer than the start-end segment
86 distance for outside corners of curving lines, and shorter for inside
87 corners.
88 All offsets are measured in map units (see "g.proj -p") or percents of
90 the line length, if followed by a % character.
91 To place a point in the middle of a line, 50% offset can be used or the
93 v.to.db module may be used to find the line’s length. Then half of that
94 distance can be used as the along-line offset.
95
97 The examples are based on the North Carolina sample location.
98 Extraction of a line segment
100 Extract line segment from 400m to 5000m from beginning of line 1:
101 # extract lines from railroad map:
102 v.extract input=railroads output=myrr cats=1
103 # join segments into polyline and reassign category numbers
104 v.build.polylines myrr out=myrr_pol
105 v.category input=myrr_pol output=myrailroads option=add
106 # zoom to an area of interest
107 g.region vector=myrailroads -p
108 # show line, category, direction (to find the beginning)
109 d.mon wx0
110 d.vect map=myrailroads display=shape,cat,dir lsize=12
111 # extract line segment from 400m to 5000m from beginning of line 1
112 echo "L 1 1 400 5000" | v.segment input=myrailroads output=myrailroads_segl
113 d.erase
114 d.vect map=myrailroads
115 d.vect map=myrailroads_segl col=green width=2
116 # set node at 5000m from beginning of line 1
117 echo "P 1 1 5000" | v.segment input=myrailroads output=myrailroads_segp
118 d.vect map=myrailroads_segp icon=basic/circle color=red fcolor=red size=5
119 Extract line segment from 400m to 5000m from beginning of line 1
120 Parallel line segments
122 Creation of parallel, 1km long line segments along the first 8km of
123 track, offset 500m to the left of the tracks:
124 v.segment input=myrailroads output=myrailroads_segl_side << EOF
125 L 1 1 1000 2000 -500
126 L 2 1 3000 4000 -500
127 L 3 1 5000 6000 -500
128 L 4 1 7000 8000 -500
129 EOF
130 d.erase
131 d.vect map=myrailroads display=shape,dir
132 d.vect -c map=myrailroads_segl_side width=2
133 Points equidistant along the tracks
135 Creation of a series of points, spaced every 2km along the tracks:
136 v.segment input=myrailroads output=myrailroads_pt2km << EOF
137 P 1 1 1000
138 P 2 1 3000
139 P 3 1 5000
140 P 4 1 7000
141 EOF
142 d.erase
143 d.vect map=myrailroads display=shape,dir
144 d.vect map=myrailroads_pt2km icon=basic/circle color=blue fcolor=blue size=5
145 A series of points, spaced every 2km along the tracks
146 Points equidistant along and offset the tracks
148 Creation of a series of points, spaced every 2km along the tracks, off‐
149 set 500m to the right:
150 v.segment input=myrailroads output=myrailroads_pt2kmO500m << EOF
151 P 1 1 1000 500
152 P 2 1 3000 500
153 P 3 1 5000 500
154 P 4 1 7000 500
155 EOF
156 d.erase
157 d.vect map=myrailroads display=shape,dir
158 d.vect map=myrailroads_pt2kmO500m icon=basic/circle color=aqua fcolor=aqua size=5
159 A series of points, spaced every 2km along the tracks, offset 500m to
160 the right
161 Points equidistant in percent along and offset the tracks
163 Creation of a series of points, spaced every 10% of the line’s length
164 along the tracks from the end of the line up to the middle point, off‐
165 set 500m to the right:
166 v.segment input=myrailroads output=myrailroads_pt10pctO500m << EOF
167 P 1 1 -0% 500
168 P 2 1 -10% 500
169 P 3 1 -20% 500
170 P 4 1 -30% 500
171 P 5 1 -40% 500
172 P 6 1 -50% 500
173 EOF
174 d.erase
175 d.vect map=myrailroads display=shape,dir
176 d.vect map=myrailroads_pt10pctO500m icon=basic/circle color=red fcolor=black size=5
177 A series of points, spaced every 10% of the line’s length along the
178 tracks from the end of the line up to the middle point, offset 500m to
179 the right
180
182 There is a problem with side-offset parallel line generation for inside
183 corners.
184
186 LRS tutorial (Linear Referencing System),
187 d.vect, v.build.polylines, v.lrs.segment, v.parallel, v.split, v.to.db,
188 v.to.points
189
191 Radim Blazek, ITC-Irst, Trento, Italy
192
194 Available at: v.segment source code (history)
195 Main index | Vector index | Topics index | Keywords index | Graphical
197 index | Full index
198 © 2003-2020 GRASS Development Team, GRASS GIS 7.8.5 Reference Manual
200GRASS 7.8.5 v.segment(1)