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v.build.polylines

NAME

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

KEYWORDS

vector, geometry, topology

SYNOPSIS

v.build.polylines
v.build.polylines help
v.build.polylines [-q] input=name output=name [cats=string] [--overwrite] [--verbose] [--quiet]

Flags:

-q

Do not print polyline info

--overwrite

Allow output files to overwrite existing files

--verbose

Verbose module output

--quiet

Quiet module output

Parameters:

input=name

Name of input vector map

output=name

Name for output vector map

cats=string

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

DESCRIPTION

v.build.polylines builds polylines from the lines or boundaries in a vector map.

A line is a single straight line segment defined by one start node, one end node and no other nodes. A polyline is also defined by one start node, one end node and no other nodes, but is made of two or more consecutive straight line segments. The connections between the constituent line segments of a polyline do not appear as nodes in the vector map.

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 polylines.

NOTES

If the lines that make up a polyline are of different types, then v.build.polylines will set the type from the first constituent line.

Category number(s) are assigned to a polyline based on cats parameter.

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 vector map.

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.

v.build.polylines correctly handles input vector maps containing lines, boundaries, centroids and points. Lines and boundaries will be converted to polylines of the desired type. Areas are only guaranteed to be preserved if the constituent lines of the polylines that define them are all boundaries in the input vector map.

ACKNOWLEDGEMENTS

This program was originally written during Mark Lake's tenure of a Leverhulme Special Research Fellowship at University College London.

SEE ALSO

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

AUTHORS

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

Last changed: $Date: 2007-10-10 13:49:16 +0200 (Wed, 10 Oct 2007) $

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