v.build.polylines - Builds polylines from lines or boundaries.
vector, geometry, topology
v.build.polylines [-q] input=name output=name [cats=string] [type=string[,string,...]] [--overwrite] [--verbose] [--quiet]
- Allow output files to overwrite existing files
- Verbose module output
- Quiet module output
- Name of input vector map
- Name for output vector map
- Category number mode
- Options: no,first,multi
- Default: no
- no: Do not assign any category number to polyline
- first: Assign category number of first line to polyline
- multi: Assign multiple category numbers to polyline
- Feature type
- Options: line,boundary
- Default: line,boundary
v.build.polylines builds polylines from the lines or
boundaries in a vector map.
A line is defined by one start node, one end node and any number of
vertices between the start and end node. The shortest possible line
consists of only two vertices where the coordinates of the start and end
node are identical to those of the two vertices.
v.build.polyline picks a line and from its start node, walks
back as long as exactly one other line of the same type is connected to
this node. Line directions are reversed as required, i.e. it does not
matter if the next line is connected to the current node by its start or
end node. Once the start line of a polyline is identified, it walks
forward and adds all vertices (in reverse order if needed) of
connected lines to the start line, i.e. the start line and connecting
lines are reversed as needed. That is, if a line is reversed depends
on what node is initially picked for building polylines. If the
direction of lines is important (it's not for boundaries to build
areas), you have to manually change line directions with
either v.edit, v.digit,
or the wxGUI vector
Polylines provide the most appropriate representation of curved lines when it
is important that nodes serve to define topology rather than geometry. Curved
lines are usually digitized as polylines, but these are sometimes broken into
their constituent straight line segments during conversion from one data
format to another. v.build.polylines can be used to rebuild such broken
v.build.polylines combines only lines if the same type to
a new polyline, i.e. lines and boundaries are kept separate.
Category number(s) are assigned to a polyline based on cats parameter.
v.build.polylines correctly handles input vector maps
containing lines, boundaries, centroids and points. Lines and
boundaries will be converted to polylines. Areas
are guaranteed to be preserved.
- cats=no - No category number is assigned to a
polyline. Also attributes tables linked to the input vector map are
not copied to the output vector map.
- cats=first - Assign to a polyline category number of the
first line. All linked attributes tables are copied to the output
- cats=multi - If the lines that make up a polyline have
different category numbers then v.build.polylines will
set the multiple catetory numbers to a polyline. Also all linked
attributes tables are copied to the output vector map.
This program was originally written during Mark Lake's tenure of a
Leverhulme Special Research Fellowship at University College London.
Mark Lake, Institute of Archaeology, University College London.
Major rewrite by Radim Blazek, October 2002
Category mode added by Martin Landa, FBK-irst, Trento, Italy, October 2007
Support for categories, attributes, and different line types by Markus Metz
Last changed: $Date: 2012-08-22 13:38:23 -0700 (Wed, 22 Aug 2012) $
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