<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <title>GRASS GIS: v.segment</title> <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"> <link rel="stylesheet" href="grassdocs.css" type="text/css"> </head> <body bgcolor="white"> <img src="grass_logo.png" alt="GRASS logo"><hr align=center size=6 noshade> <h2>NAME</h2> <em><b>v.segment</b></em> - Creates points/segments from input vector lines and positions. <h2>KEYWORDS</h2> vector, geometry <h2>SYNOPSIS</h2> <b>v.segment</b><br> <b>v.segment help</b><br> <b>v.segment</b> <b>input</b>=<em>name</em> <b>output</b>=<em>name</em> [<b>llayer</b>=<em>integer</em>] [<b>file</b>=<em>name</em>] [--<b>overwrite</b>] [--<b>verbose</b>] [--<b>quiet</b>] <h3>Flags:</h3> <DL> <DT><b>--overwrite</b></DT> <DD>Allow output files to overwrite existing files</DD> <DT><b>--verbose</b></DT> <DD>Verbose module output</DD> <DT><b>--quiet</b></DT> <DD>Quiet module output</DD> </DL> <h3>Parameters:</h3> <DL> <DT><b>input</b>=<em>name</em></DT> <DD>Name of input vector map containing lines</DD> <DT><b>output</b>=<em>name</em></DT> <DD>Name for output vector map where segments will be written</DD> <DT><b>llayer</b>=<em>integer</em></DT> <DD>Line layer</DD> <DD>A single vector map can be connected to multiple database tables. This number determines which table to use.</DD> <DD>Default: <em>1</em></DD> <DT><b>file</b>=<em>name</em></DT> <DD>Name of file containing segment rules. If not given, read from stdin.</DD> </DL> <h2>DESCRIPTION</h2> <em>v.segment</em> generates segments or points from input lines and from positions read from a text file or '<tt>stdin</tt>'. <P> The format is: <div class="code"><pre> P <point id> <line cat> <offset> [<side offset>] L <segment id> <line cat> <start offset> <end offset> [<side offset>] </pre></div> <h4>EXAMPLE</h4> The user could send to <tt>stdin</tt> something like: <div class="code"><pre> P 1 356 24.56 P 2 495 12.31 ... </pre></div> (pipe or redirect from file into the command).<br> <H2>NOTES</H2> A segment is only created for the first line found of the specified category. <P> Points are generated along the lines at the given distance(s) from the beginning of the vector line. <p> The side offset is the orthogonal distance from the line. Positive side offsets are to the right side of the line going forward, negative offsets are to the left (<em>d.vect</em> with <em>display=shape,dir</em> shows the direction of vector lines). As the segment distance is measured along the original line, side-offset lines will be longer than the start-end segment distance for outside corners of curving lines, and shorter for inside corners. <P> All offsets are measured in map units (see "<em>g.proj -p</em>"). <P> To place a point in the middle of a line, the <em>v.to.db</em> module may be used to find the line's length. Then half of that distance can be used as the along-line offset. <h2>EXAMPLES</h2> Spearfish location: <div class="code"><pre> # extract lines from railroad map: v.extract railroads out=myrr list=1 # join segments into polyline and reassign category numbers v.build.polylines myrr out=myrr_pol v.category myrr_pol out=myrailroads option=add # zoom to an area of interest g.region n=4928200 s=4921100 w=605600 e=613200 # show line, category, direction (to find the beginning) d.vect myrailroads disp=shape,cat,dir lsize=12 # extract line segment from 400m to 5000m from beginning of line 1 echo "L 1 1 400 5000" | v.segment myrailroads out=myrailroads_segl d.erase d.vect myrailroads d.vect myrailroads_segl col=green width=2 # set node at 5000m from beginning of line 1 echo "P 1 1 5000" | v.segment myrailroads out=myrailroads_segp d.vect myrailroads_segp icon=basic/circle color=red fcolor=red size=5 # get points from a text file cat mypoints.txt | v.segment myrailroads out=myrailroads_mypoints # create parallel 1km long line segments along first 8km of track, # offset 500m to the left of the tracks. v.segment myrailroads out=myrailroads_segl_side << EOF L 1 1 1000 2000 -500 L 2 1 3000 4000 -500 L 3 1 5000 6000 -500 L 4 1 7000 8000 -500 EOF d.erase d.vect myrailroads disp=shape,dir d.vect -c myrailroads_segl_side width=2 # A series of points, spaced every 2km along the tracks v.segment myrailroads out=myrailroads_pt2km << EOF P 1 1 1000 P 2 1 3000 P 3 1 5000 P 4 1 7000 EOF d.vect myrailroads_pt2km icon=basic/circle color=blue fcolor=blue size=5 # A series of points, spaced every 2km along the tracks, offset 500m to the right v.segment myrailroads out=myrailroads_pt2kmO500m << EOF P 1 1 1000 500 P 2 1 3000 500 P 3 1 5000 500 P 4 1 7000 500 EOF d.vect myrailroads_pt2kmO500m icon=basic/circle color=aqua fcolor=aqua size=5 </pre></div> <h2>BUGS</h2> There is a problem with side-offset parallel line generation for inside corners. <!-- in Vect_line_parallel(), v.parallel is also affected --> <h2>SEE ALSO</h2> <em> <a href="lrs.html">LRS tutorial</a> (Linear Referencing System),<BR> <a href="d.vect.html">d.vect</a>, <a href="v.build.polylines.html">v.build.polylines</a>, <a href="v.lrs.segment.html">v.lrs.segment</a>, <a href="v.parallel.html">v.parallel</a>, <a href="v.split.html">v.split</a>, <a HREF="v.to.db.html">v.to.db</a>, <a HREF="v.to.points.html">v.to.points</a> </em> <h2>AUTHOR</h2> Radim Blazek, ITC-Irst, Trento, Italy <p> <i>Last changed: $Date: 2007-12-17 14:45:01 +0100 (Mon, 17 Dec 2007) $</i> <HR> <P><a href="index.html">Main index</a> - <a href="vector.html">vector index</a> - <a href="full_index.html">Full index</a></P> <P>© 2003-2008 <a href="http://grass.osgeo.org">GRASS Development Team</a></p> </body> </html>
