Ground points are classified by fitting quadric surfaces. The specific idea is: first, mesh the point cloud, select the lowest point of the grid within a certain size window to construct the quadric surface, and compare the distance between the point cloud and the fitting surface in the calculation window and the set distance threshold, which is less than this Thresholds are classified as ground points; otherwise, they are classified as non-ground points. This method is suitable for undulating terrain, but not very steep areas. Click this button, and the dialog as shown below pops up.
- From Class: Source class (es).
- To Class: Target class.
- dz Tolerance (m, default value is"0.3"): After fitting the surface using the grid low point, calculate the height difference between each unclassified point and the surface. If the height difference is greater than the threshold, the unclassified point is classified as non-ground point. Otherwise, it’s classified as ground point.
- Grid Size (m, default value is"1"): The size of the grid that meshes the point cloud. The smaller the grid size, the finer the ground will be fitted, which keeps more details, but the filter efficiency will be a bit affected.
- Window Size (default value is"3"): This function uses a moving window to fit the surface, so the window size directly affects the final filtering result. The larger the window, the larger the area where surface is fitted each time. The grid size and window size need to complement each other for best results.