Geografic-Information-System/vector/v.to.points/v.to.points.html

<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> parameter 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>
&nbsp;&nbsp;&nbsp; (length of input line / 2) &lt;= <em>dmax</em> &lt;= 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: $Date$</i></p>