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)

       Accessed: unknown

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