1v.build.polylines(1) GRASS GIS User's Manual v.build.polylines(1)
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6 v.build.polylines - Builds polylines from lines or boundaries.
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9 vector, topology, geometry, line, node, vertex
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12 v.build.polylines
13 v.build.polylines --help
14 v.build.polylines input=name output=name [cats=string]
15 [type=string[,string,...]] [--overwrite] [--help] [--verbose]
16 [--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 map
37 Or data source for direct OGR access
38 output=name [required]
40 Name for output vector map
41 cats=string
43 Category number mode
44 Options: no, first, multi, same
45 Default: no
46 no: Do not assign any category number to polyline
47 first: Assign category number of first line to polyline
48 multi: Assign multiple category numbers to polyline
49 same: Create polyline from lines with same categories
50 type=string[,string,...]
52 Input feature type
53 Options: line, boundary
54 Default: line,boundary
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57 v.build.polylines builds polylines from the lines or boundaries in a
58 vector map.
59 A line is defined by one start node, one end node and any number of
61 vertices between the start and end nodes. The shortest possible line
62 consists of only two vertices where the coordinates of the start and
63 end nodes are identical to those of the two vertices.
64 v.build.polylines picks a line and from its start node, walks back as
66 long as exactly one other line of the same type is connected to this
67 node. Line directions are reversed as required, i.e. it does not matter
68 if the next line is connected to the current node by its start or end
69 node. Once the start line of a polyline is identified, it walks forward
70 and adds all vertices (in reverse order if needed) of connected lines
71 to the start line, i.e. the start line and connecting lines are re‐
72 versed as needed. That is, if a line is reversed depends on what node
73 is initially picked for building polylines. If the direction of lines
74 is important (it’s not for boundaries to build areas), you have to man‐
75 ually change line directions with either v.edit or the wxGUI vector
76 digitizer.
77 Polylines provide the most appropriate representation of curved lines
79 when it is important that nodes serve to define topology rather than
80 geometry. Curved lines are usually digitized as polylines, but these
81 are sometimes broken into their constituent straight line segments dur‐
82 ing conversion from one data format to another. v.build.polylines can
83 be used to rebuild such broken polylines.
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86 v.build.polylines combines only lines of the same type to a new poly‐
87 line, i.e. lines and boundaries are kept separate.
88 Category number(s) are assigned to a polyline based on cats parameter.
90 • cats=no - No category number is assigned to a polyline. Also
92 attributes tables linked to the input vector map are not copied
93 to the output vector map.
94 • cats=first - Assign to a polyline category number of the first
96 line. All linked attributes tables are copied to the output
97 vector map without filtering, but the categories are processed
98 according to the cats option.
99 • cats=multi - If the lines that make up a polyline have differ‐
101 ent category numbers then v.build.polylines will set the multi‐
102 ple category numbers to a polyline. Also all linked attributes
103 tables are copied to the output vector map.
104 • cats=same - Assigned lines to a polyline have same category
106 numbers in all layers. Linked attributes tables are copied to
107 the output vector map.
108 v.build.polylines correctly handles input vector maps containing lines,
109 boundaries, centroids and points. Lines and boundaries will be con‐
110 verted to polylines. Areas are guaranteed to be preserved.
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113 This program was originally written during Mark Lake’s tenure of a Lev‐
114 erhulme Special Research Fellowship at University College London.
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117 v.build, v.in.ascii, v.edit, v.split
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120 Mark Lake, Institute of Archaeology, University College London.
121 Major rewrite by Radim Blazek, October 2002
122 Category mode added by Martin Landa, FBK-irst, Trento, Italy, October
123 2007
124 Support for categories, attributes, and different line types by Markus
125 Metz
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128 Available at: v.build.polylines source code (history)
129 Accessed: Saturday Jan 21 20:39:41 2023
131 Main index | Vector index | Topics index | Keywords index | Graphical
133 index | Full index
134 © 2003-2023 GRASS Development Team, GRASS GIS 8.2.1 Reference Manual
136GRASS 8.2.1 v.build.polylines(1)