v.trees.cd.html

<h2>DESCRIPTION</h2>

<em>v.trees.cd</em> calculates the change between two given treecrown vector
maps (<b>input</b> and <b>reference</b> for time t1 and t2, respectively).
<p>
It returns three vector maps: <i>&ltbasename&gt_congruent</i> for congruent
trees, <i>&ltbasename&gt_only_&ltinput&gt</i> for gone trees and
<i>&ltbasename&gt_only_&ltreference&gt</i> for new trees,
with <i>&ltbasename&gt</i> defined by <b>output</b>.

For the congruent trees the parameter <b>congr_thresh</b> can be set,
defining the threshold of overlap (in percentage) above which trees are
considered to be congruent. Per default it is set to 90%.
<p>
For the two other maps (gone and new trees) two parameters can be set,
to remove small areas: <b>diff_min_size</b> and <b>diff_max_fd</b>.
They define the minimum size of identified change areas in sqm (default
0.25 sqm), and the maximum value of fractal dimension of identified change
areas (default 2.5).
<p>

The calculation can be done in parallel on a grid, with the edge length of
grid tiles given by <b>tile_size</b> and the number of parallel processes
given by <b>nprocs</b>.

<h2>EXAMPLE</h2>

<h3>Calculate change detection with tile_size of 500</h3>

<div class="code"><pre>
v.trees.cd input=treecrowns_2020 reference=treecrowns_2022 output=cd_2020_2022 tile_size=500
</pre></div>

<h3>Calculate change detection with explicit values for filtering congruent and changed maps</h3>

<div class="code"><pre>
v.trees.cd input=treecrowns_2020 reference=treecrowns_2022 output=cd_2020_2022 congr_thresh=80 diff_min_size=1 tile_size=500
</pre></div>

<h2>SEE ALSO</h2>

<em>
<a href="https://grass.osgeo.org/grass-stable/manuals/v.overlay.html">v.overlay</a>,
<a href="v.trees.cd.worker.html">v.trees.cd.worker</a>
</em>

<h2>AUTHORS</h2>

Julia Haas, <a href="https://www.mundialis.de/">mundialis GmbH &amp; Co. KG</a>, Germany
Lina Krisztian, <a href="https://www.mundialis.de/">mundialis GmbH &amp; Co. KG</a>, Germany