1v.build.polylines(1)          Grass User's Manual         v.build.polylines(1)
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NAME

6       v.build.polylines  - Builds polylines from lines or boundaries.
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KEYWORDS

9       vector, topology, geometry, line, node, vertex
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SYNOPSIS

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
18   Flags:
19       --overwrite
20           Allow output files to overwrite existing files
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22       --help
23           Print usage summary
24
25       --verbose
26           Verbose module output
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28       --quiet
29           Quiet module output
30
31       --ui
32           Force launching GUI dialog
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34   Parameters:
35       input=name [required]
36           Name of input vector map
37           Or data source for direct OGR access
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39       output=name [required]
40           Name for output vector map
41
42       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
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51       type=string[,string,...]
52           Input feature type
53           Options: line, boundary
54           Default: line,boundary
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DESCRIPTION

57       v.build.polylines  builds  polylines  from the lines or boundaries in a
58       vector map.
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60       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.
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65       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
72       reversed 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.
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78       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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NOTES

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.
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89       Category number(s) are assigned to a polyline based on cats parameter.
90
91           ·   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.
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95           ·   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.
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100           ·   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.
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105           ·   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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ACKNOWLEDGEMENTS

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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SEE ALSO

117        v.build, v.in.ascii, v.edit, v.split
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AUTHORS

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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SOURCE CODE

128       Available at: v.build.polylines source code (history)
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130       Main  index  | Vector index | Topics index | Keywords index | Graphical
131       index | Full index
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133       © 2003-2019 GRASS Development Team, GRASS GIS 7.8.2 Reference Manual
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137GRASS 7.8.2                                               v.build.polylines(1)
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