v.segment(1)

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
11

SYNOPSIS

13       v.segment
14       v.segment help
15       v.segment  input=name   output=name    [llayer=integer]     [file=name]
16       [--overwrite]  [--verbose]  [--quiet]
17
18   Flags:
19       --overwrite
20           Allow output files to overwrite existing files
21
22       --verbose
23           Verbose module output
24
25       --quiet
26           Quiet module output
27
28   Parameters:
29       input=name
30           Name of input vector map containing lines
31
32       output=name
33           Name for output vector map where segments will be written
34
35       llayer=integer
36           Line layer
37           A  single  vector map can be connected to multiple database tables.
38           This number determines which table to use.
39           Default: 1
40
41       file=name
42           Name of file containing segment rules.  If  not  given,  read  from
43           stdin.
44

DESCRIPTION

46       v.segment  generates segments or points from input lines and from posi‐
47       tions read from a text file or 'stdin'.
48
49       The format is:
50       P <point id>   <line cat> <offset> [<side offset>]
51       L <segment id> <line cat> <start offset> <end offset> [<;side offset>;]
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53
54   EXAMPLE
55       The user could send to stdin something like:
56       P 1 356 24.56
57       P 2 495 12.31
58        (pipe or redirect from file into the command).
59

NOTES

61       A segment is only created for the first line  found  of  the  specified
62       category.
63
64       Points  are generated along the lines at the given distance(s) from the
65       beginning of the vector line.
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67       The side offset is the orthogonal distance from the line. Positive side
68       offsets  are to the right side of the line going forward, negative off‐
69       sets are to the left (d.vect with display=shape,dir shows the direction
70       of  vector lines). As the segment distance is measured along the origi‐
71       nal line, side-offset lines will be longer than the  start-end  segment
72       distance  for  outside corners of curving lines, and shorter for inside
73       corners.
74
75       All offsets are measured in map units (see "g.proj -p").
76
77       To place a point in the middle of a line, the  v.to.db  module  may  be
78       used  to find the line's length. Then half of that distance can be used
79       as the along-line offset.
80

EXAMPLES

82       Spearfish location:
83       # extract lines from railroad map:
84       v.extract railroads out=myrr list=1
85       # join segments into polyline and reassign category numbers
86       v.build.polylines myrr out=myrr_pol
87       v.category myrr_pol out=myrailroads option=add
88       # zoom to an area of interest
89       g.region n=4928200 s=4921100 w=605600 e=613200
90       # show line, category, direction (to find the beginning)
91       d.vect myrailroads disp=shape,cat,dir lsize=12
92       # extract line segment from 400m to 5000m from beginning of line 1
93       echo "L 1 1 400 5000" | v.segment myrailroads out=myrailroads_segl
94       d.erase
95       d.vect myrailroads
96       d.vect myrailroads_segl col=green width=2
97       # set node at 5000m from beginning of line 1
98       echo "P 1 1 5000" | v.segment myrailroads out=myrailroads_segp
99       d.vect myrailroads_segp icon=basic/circle color=red fcolor=red size=5
100       # get points from a text file
101       cat mypoints.txt | v.segment myrailroads out=myrailroads_mypoints
102       # create parallel 1km long line segments along first 8km of track,
103       # offset 500m to the left of the tracks.
104       v.segment myrailroads out=myrailroads_segl_side << EOF
105       L 1 1 1000 2000 -500
106       L 2 1 3000 4000 -500
107       L 3 1 5000 6000 -500
108       L 4 1 7000 8000 -500
109       EOF
110       d.erase
111       d.vect myrailroads disp=shape,dir
112       d.vect -c myrailroads_segl_side width=2
113       # A series of points, spaced every 2km along the tracks
114       v.segment myrailroads out=myrailroads_pt2km << EOF
115       P 1 1 1000
116       P 2 1 3000
117       P 3 1 5000
118       P 4 1 7000
119       EOF
120       d.vect  myrailroads_pt2km  icon=basic/circle   color=blue   fcolor=blue
121       size=5
122       # A series of points, spaced every 2km along the tracks, offset 500m to
123       the right
124       v.segment myrailroads out=myrailroads_pt2kmO500m << EOF
125       P 1 1 1000 500
126       P 2 1 3000 500
127       P 3 1 5000 500
128       P 4 1 7000 500
129       EOF
130       d.vect myrailroads_pt2kmO500m icon=basic/circle color=aqua  fcolor=aqua
131       size=5
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133

BUGS

135       There is a problem with side-offset parallel line generation for inside
136       corners.
137

AUTHOR

144       Radim Blazek, ITC-Irst, Trento, Italy
145
146       Last changed: $Date: 2007-12-17 14:45:01 +0100 (Mon, 17 Dec 2007) $
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148       Full index
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150       © 2003-2008 GRASS Development Team
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154GRASS 6.3.0                                                       v.segment(1)