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]   [type=string[,string,...]]   [--overwrite]
       [--verbose]  [--quiet]

   Flags:
       -q
           Unused

       --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

       type=string[,string,...]
           Feature type
           Options: line,boundary
           Default: line,boundary

DESCRIPTION

       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.digit, or the wxGUI vector digitizer.

       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

       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.

                     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.  Areas are guaranteed to be preserved.

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
       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) $

       Full index

       © 2003-2013 GRASS Development Team

GRASS 6.4.3                                                                            v.build.polylines(1grass)