v.segment(1grass)

1v.segment(1)                  Grass User's Manual                 v.segment(1)
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NAME

6       v.segment   - Creates points/segments from input vector lines and posi‐
7       tions.
8

KEYWORDS

10       vector, geometry, node, point, segment, vertex
11

SYNOPSIS

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
18   Flags:
19       --overwrite
20           Allow output files to overwrite existing files
21
22       --help
23           Print usage summary
24
25       --verbose
26           Verbose module output
27
28       --quiet
29           Quiet module output
30
31       --ui
32           Force launching GUI dialog
33
34   Parameters:
35       input=name [required]
36           Name of input vector lines map
37           Or data source for direct OGR access
38
39       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
46       output=name [required]
47           Name for output vector map
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49       rules=name
50           Name of file containing segment rules
51           ’-’ for standard input
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DESCRIPTION

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
58       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.
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65   EXAMPLE
66       The user could send to stdin something like:
67       P 1 356 24.56
68       P 2 495 12.31
69       P 3 500 -12.31
70       P 4 510 -20%
71       ...
72       (pipe or redirect from file into the command).
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NOTES

75       A  segment  is  only  created for the first line found of the specified
76       category.
77
78       Points are generated along the lines at the given distance(s)  or  per‐
79       cent(s)  of  the  line length from the beginning or end, if offsets are
80       negative, of the vector line.
81
82       The side offset is the orthogonal distance from the line. Positive side
83       offsets  are to the right side of the line going forward, negative off‐
84       sets are to the left (d.vect with display=shape,dir shows the direction
85       of  vector lines). As the segment distance is measured along the origi‐
86       nal line, side-offset lines will be longer than the  start-end  segment
87       distance  for  outside corners of curving lines, and shorter for inside
88       corners.
89
90       All offsets are measured in map units (see "g.proj -p") or percents  of
91       the line length, if followed by a % character.
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93       To place a point in the middle of a line, 50% offset can be used or the
94       v.to.db module may be used to find the line’s length. Then half of that
95       distance can be used as the along-line offset.
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EXAMPLES

98       The examples may be used in the North Carolina sample location.
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100       Example: Extract line segment from 400m to 5000m from beginning of line
101       1:
102       # extract lines from railroad map:
103       v.extract railroads out=myrr cats=1
104       # join segments into polyline and reassign category numbers
105       v.build.polylines myrr out=myrr_pol
106       v.category myrr_pol out=myrailroads option=add
107       # zoom to an area of interest
108       g.region vector=myrailroads -p
109       # show line, category, direction (to find the beginning)
110       d.mon wx0
111       d.vect myrailroads disp=shape,cat,dir lsize=12
112       # extract line segment from 400m to 5000m from beginning of line 1
113       echo "L 1 1 400 5000" | v.segment myrailroads out=myrailroads_segl
114       d.erase
115       d.vect myrailroads
116       d.vect myrailroads_segl col=green width=2
117       # set node at 5000m from beginning of line 1
118       echo "P 1 1 5000" | v.segment myrailroads out=myrailroads_segp
119       d.vect myrailroads_segp icon=basic/circle color=red fcolor=red size=5
120       Extract line segment from 400m to 5000m from beginning of line 1
121
122       Example: Create parallel 1km long line  segments  along  first  8km  of
123       track, offset 500m to the left of the tracks.
124       v.segment myrailroads out=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 myrailroads disp=shape,dir
132       d.vect -c myrailroads_segl_side width=2
133
134       Example: A series of points, spaced every 2km along the tracks
135       v.segment myrailroads out=myrailroads_pt2km << EOF
136       P 1 1 1000
137       P 2 1 3000
138       P 3 1 5000
139       P 4 1 7000
140       EOF
141       d.erase
142       d.vect myrailroads disp=shape,dir
143       d.vect myrailroads_pt2km icon=basic/circle color=blue fcolor=blue size=5
144       A series of points, spaced every 2km along the tracks
145
146       Example:  A series of points, spaced every 2km along the tracks, offset
147       500m to the right
148       v.segment myrailroads out=myrailroads_pt2kmO500m << EOF
149       P 1 1 1000 500
150       P 2 1 3000 500
151       P 3 1 5000 500
152       P 4 1 7000 500
153       EOF
154       d.erase
155       d.vect myrailroads disp=shape,dir
156       d.vect myrailroads_pt2kmO500m icon=basic/circle color=aqua fcolor=aqua size=5
157       A series of points, spaced every 2km along the tracks, offset  500m  to
158       the right
159
160       Example:  A  series  of  points,  spaced every 10% of the line’s length
161       along the tracks from the end of the line up to the middle point,  off‐
162       set 500m to the right
163       v.segment myrailroads out=myrailroads_pt10pctO500m << EOF
164       P 1 1  -0% 500
165       P 2 1 -10% 500
166       P 3 1 -20% 500
167       P 4 1 -30% 500
168       P 5 1 -40% 500
169       P 6 1 -50% 500
170       EOF
171       d.erase
172       d.vect myrailroads disp=shape,dir
173       d.vect myrailroads_pt10pctO500m icon=basic/circle color=red fcolor=black size=5
174       A  series  of  points,  spaced every 10% of the line’s length along the
175       tracks from the end of the line up to the middle point, offset 500m  to
176       the right
177

KNOWN ISSUES

179       There is a problem with side-offset parallel line generation for inside
180       corners.
181

AUTHOR

188       Radim Blazek, ITC-Irst, Trento, Italy
189
190       Last changed: $Date: 2015-05-11 02:11:34 +0200 (Mon, 11 May 2015) $
191

SOURCE CODE

193       Available at: v.segment source code (history)
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195       Main  index  | Vector index | Topics index | Keywords index | Graphical
196       index | Full index
197
198       © 2003-2019 GRASS Development Team, GRASS GIS 7.4.4 Reference Manual
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202GRASS 7.4.4                                                       v.segment(1)