Ground Classification

Author: V. Wichmann (c) 2021
Menu: Shapes | Point Clouds | Classification

Description

The tool allows one to filter a point cloud into ground (bare earth) and non-ground points. The ground points can be used later to create a digital elevation model from the data, for example. The tool uses concepts as described by Vosselman (2000) and is based on the assumption that a large height difference between two nearby points is unlikely to be caused by a steep slope in the terrain. The probability that the higher point might be non-ground increases when the distance between the two points decreases. Therefore the filter defines a maximum height difference (dz_max) between two points as a function of the distance (d) between the points (dz_max(d) = d). A point is classified as terrain if there is no other point within the kernel radius to which the height difference is larger than the allowed maximum height difference at the distance between these two points. The approximate terrain slope (s) parameter is used to modify the filter function to match the overall slope in the study area (dz_max(d) = d * s). A 5% confidence interval (ci = 1.65 * sqrt(2 * stddev)) may be used to modify the filter function even further by either relaxing (dz_max(d) = d * s + ci) or amplifying (dz_max(d) = d * s - ci) the filter criterium.

References

Vosselman, G. (2000): Slope based filtering of laser altimetry data. IAPRS, Vol. XXXIII, Part B3, Amsterdam, The Netherlands, 935-942

Parameters

	Name	Type	Identifier	Description	Constraints
Input	Point Cloud	point cloud, input	`PC_IN`	The input point cloud to classify.	-
Output	Point Cloud Classified	point cloud, output, optional	`PC_OUT`	The classified point cloud.	-
Options	Filter Radius	floating point number	`RADIUS`	The radius of the filter kernel [map units]. Must be large enough to reach ground points next to non-ground objects.	Minimum: 0.001000 Default: 2.500000
	Terrain Slope [%]	floating point number	`TERRAINSLOPE`	The approximate terrain slope [%]. Used to relax the filter criterium in steeper terrain.	Minimum: 0.000000 Default: 30.000000
	Filter Modification	choice	`FILTERMOD`	Choose whether to apply the filter kernel without modification or to use a confidence interval to relax or amplify the height criterium.	Available Choices: [0] none [1] relax filter [2] amplify filter Default: 0
	Standard Deviation	floating point number	`STDDEV`	The standard deviation used to calculate a 5% confidence interval applied to the height threshold [map units].	Minimum: 0.000000 Default: 0.100000

Command Line


Usage: saga_cmd pointcloud_tools 15 [-PC_IN ] [-PC_OUT ] [-RADIUS ] [-TERRAINSLOPE ] [-FILTERMOD ] [-STDDEV ]
  -PC_IN:          	Point Cloud
	point cloud, input
  -PC_OUT:         	Point Cloud Classified
	point cloud, output, optional
  -RADIUS:      	Filter Radius
	floating point number
	Minimum: 0.001000
	Default: 2.500000
  -TERRAINSLOPE:	Terrain Slope [%]
	floating point number
	Minimum: 0.000000
	Default: 30.000000
  -FILTERMOD:      	Filter Modification
	choice
	Available Choices:
	[0] none
	[1] relax filter
	[2] amplify filter
	Default: 0
  -STDDEV:      	Standard Deviation
	floating point number
	Minimum: 0.000000
	Default: 0.100000