v.segment(1)

1v.segment(1)                  Grass User's Manual                 v.segment(1)
2
3
4

NAME

6       v.segment  - Create points/segments from input lines and and positions.
7

KEYWORDS

9       vector, geometry
10

SYNOPSIS

12       v.segment
13       v.segment help
14       v.segment input=name output=name  [llayer=integer]   [--overwrite]
15
16   Flags:
17       --overwrite
18
19   Parameters:
20       input=name
21           Input map containing lines
22
23       output=name
24           Output map where segments will be written
25
26       llayer=integer
27           Line layer Default: 1
28

DESCRIPTION

30       v.segment  generates segments or points from input lines and from posi‐
31       tions read from 'stdin'.
32
33       The format is:
34       P <point id>   <line cat> <;offset>; [<;side offset>;]
35       L <segment id> <line cat> <;start offset>; <;end offset>; [<;side  off‐
36       set>;]
37
38
39   EXAMPLE
40       The user must send to stdin something like:
41       P 1 356 24.56
42       P 2 495 12.31
43        (pipe or redirect from file into the command).
44

NOTES

46       A  segment  is  only  created for the first line found of the specified
47       category.
48
49       Points are generated along the lines at the given distance(s) from  the
50       beginning of the vector line.
51
52       The side offset is the orthogonal distance from the line. Positive side
53       offsets are to the right side of the line going forward, negative  off‐
54       sets  are  to  the  left. As the segment distance is measured along the
55       original line, side-offset lines will be longer than the start-end seg‐
56       ment  distance  for  outside  corners of curving lines, and shorter for
57       inside corners.
58
59       All offsets are measured in map units (see "g.proj -p").
60
61       To place a point in the middle of a line, the  v.to.db  module  may  be
62       used  to find the line's length. Then half of that distance can be used
63       as the along-line offset.
64

EXAMPLES

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

BUGS

119       There is a problem with side-offset parallel line generation for inside
120       corners.
121

AUTHOR

128       Radim Blazek, ITC-Irst, Trento, Italy
129
130       Last changed: $Date: 2007/05/04 05:33:50 $
131
132       Full index
133
134
135
136GRASS 6.2.2                                                       v.segment(1)