<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <title>GRASS GIS: v.to.points</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.to.points</b></em> - Create points along input lines in new vector with 2 layers. <h2>KEYWORDS</h2> vector, geometry <h2>SYNOPSIS</h2> <b>v.to.points</b><br> <b>v.to.points help</b><br> <b>v.to.points</b> [-<b>nvit</b>] <b>input</b>=<em>name</em> <b>output</b>=<em>name</em> [<b>type</b>=<em>string</em>[,<i>string</i>,...]] [<b>llayer</b>=<em>integer</em>] [<b>dmax</b>=<em>float</em>] [--<b>overwrite</b>] [--<b>verbose</b>] [--<b>quiet</b>] <h3>Flags:</h3> <DL> <DT><b>-n</b></DT> <DD>Write line nodes</DD> <DT><b>-v</b></DT> <DD>Write line vertices</DD> <DT><b>-i</b></DT> <DD>Interpolate points between line vertices</DD> <DT><b>-t</b></DT> <DD>Do not create attribute table</DD> <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>Input vector map containing lines</DD> <DT><b>output</b>=<em>name</em></DT> <DD>Output vector map where points will be written</DD> <DT><b>type</b>=<em>string[,<i>string</i>,...]</em></DT> <DD>Type</DD> <DD>Feature type(s)</DD> <DD>Options: <em>point,line,boundary,centroid,area</em></DD> <DD>Default: <em>point,line,boundary,centroid</em></DD> <DT><b>llayer</b>=<em>integer</em></DT> <DD>Layer number</DD> <DD>Line layer</DD> <DD>Default: <em>1</em></DD> <DT><b>dmax</b>=<em>float</em></DT> <DD>Maximum distance between points in map units</DD> <DD>Default: <em>100</em></DD> </DL> <h2>DESCRIPTION</h2> <em>v.to.points</em> creates points along input lines. The output is a vector with 2 layers. Layer 1 holds the category and attributes of the input lines; all points created along the same line have the same category, equal to the category of that line. In layer 2 each point has it's unique category; other attributes stored in layer 2 are <em>lcat</em> - the category of the input line and <em>along</em> - the distance from line's start. <h2>NOTES</h2> The <em>dmax</em> parameter is the maximum limit but not an exact distance. To place points with exact distance from the beginning of the vector line the user should use <a HREF="v.segment.html">v.segment</a>. <p> The <em>type</em> parameter is used to control which input vector geometry types to convert into points. Some caveats to consider about this parameter: </p> <ul> <li> Points and centroids can be considered as "lines" with only one node. Consequently, the result of selecting <em>point</em> or <em>centroid</em> as the type parameter is that all points/centroids get written into the output vector. The original category numbers of the input points/centroids get written to the '<em><i>lcat</i></em>' attribute in layer 2 of the output vector. All values for <em>along</em> are zero in the output vector, as only point geometry was used for input (there is no linear distance to calculate <i>along</i>, as each point/centroid is the start <em><i>and</i></em> end of its own "line".</li> <li> Boundaries are treated as lines, with points getting interpolated along the boundary perimeter according to <em>dmax</em>. If two adjoining polygons share a topological boundary, the boundary only gets converted to points once.</li> <li> If the <em>type</em> paramter is set to <em>area</em>, the boundary of each area is converted to points <i>regardless</i> of whether or not there is a topological boundary between adjacent areas. In other words, the common boundary of two adjoining areas, for example, gets converted to points twice. The centroid is not converted to a point in the output vector for <em>type=area</em>.</li> </ul> The -v flag is used to digitize points that fall on the line's vertices <em>only</em>. <em>dmax</em> is ignored in this case. <p> If the -i flag is used in conjunction with the -v flag, <em>v.to.points</em> will digitize points on the line vertices, as well as interpolate points between line vertices using <em>dmax</em> as the maximum allowable spacing. <p> To get points created for the beginning, middle and end only, use the -i switch and set <em>dmax</em> so that: <p> (length of input line / 2) <= <em>dmax</em> <= length of input line <p> So if <em>dmax</em> is between 0.5x and 1.0x the line length, you will always get points created at exactly the beginning, middle and end of the input line. <h2>EXAMPLE</h2> In this example, the 't_powerlines' vector lines map in the <a HREF="http://grass.itc.it/download/data6.php">Spearfish 6</a> location is used to create points along the input lines: <div class="code"><pre> v.to.points in=t_powerlines out=t_powerlines_points dmax=120 d.vect t_powerlines_points </pre></div> <h2>SEE ALSO</h2> <em> <a HREF="v.segment.html">v.segment</a>, <a HREF="v.to.rast.html">v.to.rast</a>, <a HREF="v.to.db.html">v.to.db</a></em> <h2>AUTHOR</h2> Radim Blazek <p><i>Last changed: $Date: 2006-09-28 14:19:12 +0200 (Thu, 28 Sep 2006) $</i></p> <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>
