====== Point Cloud Change Detection ======

This page describes how to use the extension "Point Cloud Change Detection"\\

{{orbit_desktop:how_to_find.png?25&nolink  |}} Main Toolbar > Extension > Point Cloud Change Detection

The "Point Cloud Change Detection" extension makes it possible to compare 2 point clouds.\\

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===== Concepts =====

The change between two point clouds can be analyzed by dividing the point cloud in voxels and counting the number of added and removed points within every voxel.

Point cloud change detection project files are stored in the same location as the source point clouds. 


===== Source =====

Use the generic workflow for [[2210:desktop_ext:generic|]] to define the source file. 

The method for the range of interest is 'Area'. 


===== Compare Point Cloud =====

Add the active point cloud dataset from the dataset list that will be compared with the source point cloud dataset. 
===== Parameters: Algorithm =====

=== Voxel Size ===

The selected area is divided in voxels with a defined size. For every voxel, the change detection will give information on how many points are added or removed. 

For less dense point clouds, a higher voxel size should be used. 

=== Voxels Change Pts Min === 

The minimum number of points that should be added or removed in a voxel in order to add the voxel to the result datasets. 

=== Voxels Context Min ===

The minimum number of voxels that should be around a voxel in order to consider the voxel. This is done to exclude isolated voxels.

=== Classified point cloud ===

Include/Exclude classes to be used. 

===== Parameters: Output =====

=== Voxel Result === 

The change_voxels vector file includes all the voxels that have added or removed points in the change analysis. Every voxel has the attributes:
  * FD_PointCount1: Number of points in voxel in source point cloud
  * FD_PointCount2: Number of points in voxel in compared point cloud
  * FD_PointCloudDelta: The difference in points between the source and compared point cloud
  * FD_PointCloudDeltaAbsolute: The absolute difference in points between the source and compared pointcloud

Depending on the chosen output parameters, the following results are available:

=== Cluster Results ===

This change_voxel_clusters vector file clusters the voxels that are within the clustering distance. Every cluster has the attributes:
  * Cluster size: Number of voxels in cluster
  * FD_AvgPointCount1: Number of points in cluster in source point cloud
  * FD_AvgPointCount2: Number of points in cluster in compared point cloud
  * FD_AvgPointCloudDelta: The difference in points between the source and compared point cloud in the cluster
  * FD_AvgPointCloudDeltaAbsolute: The absolute difference in points between the source and compared pointcloud in the cluster


=== Create Added OPC and Removed OPC ===

The results are two opc and ops files: 
  * The added points in the compared pointcloud
  * The removed points in the compared pointcloud