1v.to.points(1) Grass User's Manual v.to.points(1)
2
6 v.to.points - Create points along input lines.
7
9 vector
10
12 v.to.points
13 v.to.points help
14 v.to.points [-vit] input=name [type=string[,string,...]] output=name
15 [llayer=integer] [dmax=float] [--overwrite]
16 Flags:
18 -v Write line vertices.
19 -i Interpolate points between line vertices.
21 -t Do not create attribute table.
23 --overwrite
25 Parameters:
27 input=name
28 Input map containing lines
29 type=string[,string,...]
31 Type Options: point,line,boundary,centroid,area Default:
32 point,line,boundary,centroid
33 output=name
35 Output map where points will be written
36 llayer=integer
38 Line layer Default: 1
39 dmax=float
41 Maximum distance between points in map units. Default: 100
42
44 v.to.points creates points along input lines. The output is a vector
45 with 2 layers. Layer 1 holds the category and attributes of the input
46 lines; all points created along the same line have the same category,
47 equal to the category of that line. In layer 2 each point has it's
48 unique category; other attributes stored in layer 2 are lcat - the cat‐
49 egory of the input line and along - the distance from line's start.
50
52 The dmax parameter is the maximum limit but not an exact distance. To
53 place points with exact distance from the beginning of the vector line
54 the user should use v.segment.
55 The type parameter is used to control which input vector geometry types
57 to convert into points. Some caveats to consider about this parameter:
58 Points and centroids can be considered as "lines" with
60 only one node. Consequently, the result of selecting
61 point or centroid as the type parameter is that all
62 points/centroids get written into the output vector. The
63 original category numbers of the input points/centroids
64 get written to the 'lcat' attribute in layer 2 of the
65 output vector. All values for along are zero in the out‐
66 put vector, as only point geometry was used for input
67 (there is no linear distance to calculate along, as each
68 point/centroid is the start and end of its own "line".
69 Boundaries are treated as lines, with points getting
71 interpolated along the boundary perimeter according to
72 dmax. If two adjoining polygons share a topological
73 boundary, the boundary only gets converted to points
74 once.
75 If the type paramter is set to area, the boundary of each
77 area is converted to points regardless of whether or not
78 there is a topological boundary between adjacent areas.
79 In other words, the common boundary of two adjoining
80 areas, for example, gets converted to points twice. The
81 centroid is not converted to a point in the output vector
82 for type=area.
83 The -v flag is used to digitize points that fall on the line's vertices
84 only. dmax is ignored in this case.
85 If the -i flag is used in conjunction with the -v flag, v.to.points
87 will digitize points on the line vertices, as well as interpolate
88 points between line vertices using dmax as the maximum allowable spac‐
89 ing.
90 To get points created for the beginning, middle and end only, use the
92 -i switch and set dmax so that:
93 (length of input line / 2) <= dmax <= length of input line
95 So if dmax is between 0.5x and 1.0x the line length, you will always
97 get points created at exactly the beginning, middle and end of the
98 input line.
99
101 In this example, the 't_powerlines' vector lines map in the Spearfish 6
102 location is used to create points along the input lines:
103 v.to.points in=t_powerlines out=t_powerlines_points dmax=120
104 d.vect t_powerlines_points
105
108 v.segment, v.to.rast, v.to.db
109
111 Radim Blazek
112 Last changed: $Date: 2006/09/28 12:20:21 $
114 Full index
116GRASS 6.2.2 v.to.points(1)