The Compare Point Clouds tool performs a change detection between a set of point clouds to find points that have changed more than an allowed minimum difference. This can be used both to determine edits that have been made to a file, and also to detect change over time when there are point clouds from two different time periods. With change over time, the clouds may have some minor variation from the collection discrepancies which can be ignored with the minimum distance setting, and then the larger changes in the terrain will be detected between the two clouds.
This tool requires Global Mapper Pro.
Select the Compare Point Clouds button from the Lidar Toolbar.
Point Cloud(s) to Compare Against
Select the reference point cloud or clouds. If this comparison is for detecting change over time, this would typically the initial starting point cloud.
Point Cloud(s) to Find Changes In
Select the point cloud(s) that will be searched for differences. In a change over time analysis, this would typically be the later observation.
Minimum Distance Between Point Clouds – Specify the minimum distance which is considered a significant change between the two point clouds. Only points that have a difference greater than or equal to the minimum distance will be marked as change points. Use this setting to ignore minor differences between point clouds that may occur between different collection times, to find only the significantly changed points.
Difference Layer Description – Set the name of the output point layer than contains the changed points.
Ignore Differences with Fewer than x Neighbor Points – This setting will help to ignore noise points that may not match the comparison cloud, but do not represent enough of a cluster of changed points to be significant. For example you may only care about areas where 5 or more nearby points show up as different from the reference point cloud.
Include Points from Both Point Sets Not in the Other – By default the output layer of changed points will only include points from the clouds checked for Point Clouds to Find Changes In. Check this option to include points that are significantly different in either the reference cloud or the changed cloud. This will produce multiple changed lidar point layers, one for each input layer.
Mark Changed Points as Deleted in Original Cloud – Check this option to delete the changed points from the original layer. See Deleting and Undeleting Features for more information.
Include Changes Outside Intersection of Cloud Bounding Boxes – Check this option to include points outside of the intersection of the input point clouds as change points. The default when this is unchecked is to only only compare the horizontal extent cover the overlap in bounds of the reference cloud(s) and change cloud(s).