Deciduous tree segmentation using airborne lidar point clouds and geometric networks: Examples from the Park Sanssouci, Potsdam, Germany
Authors: Hess Max , Rheinwalt Aljoscha , Brell Maximilian , Bookhagen Bodo 
Published: March 2021

&lt;p&gt;&lt;span&gt;Automated tree segmentation in &lt;/span&gt;&lt;span&gt;anthropogenically&lt;/span&gt; &lt;span&gt;shaped e&lt;/span&gt;&lt;span&gt;nvironments is challenging. &lt;/span&gt;&lt;span&gt;Large&lt;/span&gt;&lt;span&gt; differences in &lt;/span&gt;&lt;span&gt;deciduous&lt;/span&gt; &lt;span&gt;tree &lt;/span&gt;&lt;span&gt;species &lt;/span&gt;&lt;span&gt;composition&lt;/span&gt; &lt;span&gt;narrow&lt;/span&gt;&lt;span&gt;s&lt;/span&gt; &lt;span&gt;down&lt;/span&gt;&lt;span&gt; suitable solutions. &lt;/span&gt;&lt;span&gt;Tree crowns and &lt;/span&gt;&lt;span&gt;vegetation structure&lt;/span&gt;&lt;span&gt;s&lt;/span&gt; &lt;span&gt;exhibit&lt;/span&gt; &lt;span&gt;wide&lt;/span&gt; &lt;span&gt;variet&lt;/span&gt;&lt;span&gt;ies and trees often form &lt;/span&gt;&lt;span&gt;complex&lt;/span&gt; &lt;span&gt;tree &lt;/span&gt;&lt;span&gt;aggregations. &lt;/span&gt;&lt;span&gt;Clear &lt;/span&gt;&lt;span&gt;delineation&lt;/span&gt; &lt;span&gt;of individual &lt;/span&gt;&lt;span&gt;deciduous tree&lt;/span&gt;&lt;span&gt; crowns in &lt;/span&gt;&lt;span&gt;dense tree stands&lt;/span&gt;&lt;span&gt; is &lt;/span&gt;&lt;span&gt;difficult, and methods developed for conifer trees &lt;/span&gt;&lt;span&gt;may not be applicable&lt;/span&gt;&lt;span&gt;. &lt;/span&gt;&lt;span&gt;The dense overlapping structures require alternative approaches.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&lt;span&gt;To overcome &lt;/span&gt;&lt;span&gt;some of these limitations, we have developed a &lt;/span&gt;&lt;span&gt;new &lt;/span&gt;&lt;span&gt;method using &lt;/span&gt;&lt;span&gt;individual point locations and their neighborhood information&lt;/span&gt;&lt;span&gt;. &lt;/span&gt;&lt;span&gt;We &lt;/span&gt;&lt;span&gt;build a network of connected lidar points with&lt;/span&gt;&lt;span&gt; the following steps: (1) &lt;/span&gt;&lt;span&gt;W&lt;/span&gt;&lt;span&gt;e use &lt;/span&gt;&lt;span&gt;a &lt;/span&gt;&lt;span&gt;k-d tree to derive immediate neighborhoods of points. (2) &lt;/span&gt;&lt;span&gt;F&lt;/span&gt;&lt;span&gt;or each point a vector is generated pointing to &lt;/span&gt;&lt;span&gt;the &lt;/span&gt;&lt;span&gt;centroid&lt;/span&gt;&lt;span&gt; of &lt;/span&gt;&lt;span&gt;higher locate&lt;/span&gt;&lt;span&gt;d&lt;/span&gt;&lt;span&gt; points within a &lt;/span&gt;&lt;span&gt;neighborhood.&lt;/span&gt; &lt;span&gt;(3)&lt;/span&gt; &lt;span&gt;Each point is then connected to &lt;/span&gt;&lt;span&gt;the&lt;/span&gt;&lt;span&gt; nearest point above &lt;/span&gt;&lt;span&gt;its corresponding centroid.&lt;/span&gt; &lt;span&gt;Points which do not connect &lt;/span&gt;&lt;span&gt;to higher points &lt;/span&gt;&lt;span&gt;based on &lt;/span&gt;&lt;span&gt;this&lt;/span&gt;&lt;span&gt; rule&lt;/span&gt;&lt;span&gt; are identified as &lt;/span&gt;&lt;span&gt;endpoints&lt;/span&gt;&lt;span&gt;. &lt;/span&gt;&lt;span&gt;Since each point is connected to only one higher point if such a point exists in the neighborhood, these connections form a forest of trees network&lt;/span&gt;&lt;span&gt;. &lt;/span&gt;&lt;span&gt;(4) &lt;/span&gt;&lt;span&gt;With &lt;/span&gt;&lt;span&gt;adaptive&lt;/span&gt;&lt;span&gt; parameters each tree crown is represented by a single component of the network, i.e., each tree crown is represented by a mathematical tree in the network. &lt;/span&gt;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&lt;span&gt;Our&lt;/span&gt;&lt;span&gt; new method is tested &lt;/span&gt;&lt;span&gt;with &lt;/span&gt;&lt;span&gt;a dense airborne point cloud (88 pts/m2) &lt;/span&gt;&lt;span&gt;collected in&lt;/span&gt;&lt;span&gt; 2018 for the Park Sanssouci in Potsdam, Germany.&lt;/span&gt; &lt;span&gt;This area &lt;/span&gt;&lt;span&gt;of high biodiversity &lt;/span&gt;&lt;span&gt;contains more than 25.000 mapped trees &lt;/span&gt;&lt;span&gt;from&lt;/span&gt; &lt;span&gt;over &lt;/span&gt;&lt;span&gt;7&lt;/span&gt;&lt;span&gt;5&lt;/span&gt; &lt;span&gt;different &lt;/span&gt;&lt;span&gt;species&lt;/span&gt; &lt;span&gt;that we use as reference and validation dataset&lt;/span&gt;&lt;span&gt;s&lt;/span&gt;&lt;span&gt;. We demonstrate the &lt;/span&gt;&lt;span&gt;successful&lt;/span&gt;&lt;span&gt; application of our algorithm and present &lt;/span&gt;&lt;span&gt;segmentation&lt;/span&gt;&lt;span&gt; uncertainties.&lt;/span&gt;&lt;/p&gt;