Classify Ground Points By CSF

Functional Overview

Ground point classsification is the basic operation of point cloud data processing. This function adopts Ground Point Filtering Algorithm Based on Cloth Simulation(Cloth Simulation Filter, IPTD(Zhang et al.,2016))

  • This algorithm can be divided into the following steps:
    1. Turn the point cloud upside down in the Z direction.The point cloud is gridded with a certain resolution in the XY direction, and the nodes of the grid are used as a simulated fabric.
    2. Set the initial height of the fabric to the maximum point cloud Z and start the iteration.During each iteration, the fabric will “sink” to the point cloud with a certain gravity, and the positional relationship between the fabric node and the point cloud is calculated at the same time.Nodes that have fallen on the point cloud will not be movable during the next iteration.Immovable nodes will slow down the sinking speed of surrounding nodes according to the stiffness value R.
    3. After a certain number of iterations, calculate the positional relationship between each point and the fabric; points whose distance from the fabric in the Z direction is less than a certain threshold value will be divided into target categories.

Steps

1.Click Classify Ground Points button, pop up the Classify Ground Points dialog box.

OpenPointCloud

Parameter description:

  • Input Data: The input file can be a single point cloud data or a point cloud dataset.
  • From Class: Source class(es).
  • To Class: Target class.
  • Scenes (Optional): For different terrain scenes, you can choose steep terrain, gentle terrain, and flat terrain.Check different terrain features to correspond to different default parameters
  • Grid Size (meters): The default is “1.0”, the resolution of the fabric node.1.0 is suitable for most point clouds.This value can be appropriately reduced for data with large terrain ups and downs.
  • Classify Threshold (meters): The default is “0.5”. After the iteration is completed, points with a distance of less than this threshold in the Z direction from the fabric will be divided into target categories.
  • Max Iteration: The default is “500”, and the iteration is completed when the algorithm reaches the maximum number of iterations or all fabric nodes are immovable.
  • Smoothes the Margins of Steep Slopes: When the fabric is located on a steep slope, due to internal constraints between the fabric nodes, it cannot be well matched with the ground, and the algorithm may produce large errors.Checking this item can eliminate the impact of steep slopes to a certain extent.If the scene does not contain steep slopes, you can uncheck it.
  • DefaultValue: Click this button to set all parameters as default.

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