CSF (plugin)
Introduction
Airborne LiDAR Data Filtering Algorithm Based on Cloth Simulation
Wuming Zhang, Jianbo Qi, Peng Wan, Hongtao Wang, Donghui Xi, Guangjian Yan, Xihan Mu (School of Geography, Beijing Normal University, China)
Introduction
Separating point clouds into ground and non-ground measurements is an essential step to generate digital terrain models (DTMs) from airborne LiDAR (light detection and ranging) data. Many filtering algorithms have been developed. However, even state-of-the-art filtering algorithms need to set up a number of complicated parameters carefully to achieve high accuracy.
For the purpose of reducing the parameters users to set, and promoting the filtering algorithms, we present a new filtering method which only needs a few easy-to-set integer and Boolean parameters. This method is based on cloth simulation which is a 3D computer graphics algorithm and is used for simulating cloth within a computer program. In this proposed approach, a LiDAR point cloud is inverted, and then a rigid cloth is used to cover the inverted surface. By analyzing the interactions between the cloth nodes and the corresponding LiDAR points, the locations of the cloth nodes can be determined to generate an approximation of the ground surface. Finally, the ground points can be extracted from the LiDAR point cloud by comparing the original LiDAR points and the generated surface. This filtering algorithm could be called cloth simulation filtering, CSF.
Algorithm Details
Our method is based on the simulation of a simple physical process. Imagine a piece of cloth is placed above a terrain, and then this cloth drops because of gravity. Assuming that the cloth is soft enough to stick to the surface, the final shape of the cloth is the DSM (digital surface model). However, if the terrain is firstly turned upside down and the cloth is defined with rigidness, then the final shape of the cloth is the DTM. To simulate this physical process, we employ a technique that is called cloth simulation (Weil, 1986). Based on this technique, we developed our cloth simulation filtering (CSF) algorithm to extract ground points from LiDAR points. The overview of the proposed algorithm is illustrated in Fig. 1. First, the original point cloud is turned upside down, and then a cloth drops to the inverted surface from above. By analyzing the interactions between the nodes of the cloth and the corresponding LiDAR points, the final shape of the cloth can be determined and used as a base to classify the original points into ground and non-ground parts.
Fundamental of the cloth simulation
During cloth simulation, the cloth can be modeled as a grid that consists of particles with mass and interconnections called a Mass-Spring Model (Provot, 1995). Fig. 2 shows the structure of the grid model. A particle on the node of the grid has no size but is assigned with a constant mass.