NAME

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

KEYWORDS

       vector, topology, geometry, line, node, vertex

SYNOPSIS

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

   Flags:
       --overwrite
           Allow output files to overwrite existing files

       --help
           Print usage summary

       --verbose
           Verbose module output

       --quiet
           Quiet module output

       --ui
           Force launching GUI dialog

   Parameters:
       input=name [required]
           Name of input vector map
           Or data source for direct OGR access

       output=name [required]
           Name for output vector map

       cats=string
           Category number mode
           Options: no, first, multi, same
           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
           same: Create polyline from lines with same categories

       type=string[,string,...]
           Input 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
       nodes.  The  shortest  possible line consists of only two vertices where the coordinates of the start and
       end nodes are identical to those of the two vertices.

       v.build.polylines 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 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 of 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 without filtering, but the categories are processed according
               to the cats option.

           •   cats=multi - If the  lines  that  make  up  a  polyline  have  different  category  numbers  then
               v.build.polylines  will  set  the  multiple  category  numbers  to  a  polyline.  Also all linked
               attributes tables are copied to the output vector map.

           •   cats=same - Assigned lines to a polyline  have  same  category  numbers  in  all  layers.  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.edit, v.split

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

SOURCE CODE

       Available at: v.build.polylines source code (history)

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       © 2003-2019 GRASS Development Team, GRASS GIS 7.8.2 Reference Manual