SAGA-GIS Module Library Documentation (v2.1.3)

Module DTM Filter (slope-based)

The module can be used to filter a digital surface model (DSM), i.e. to classify its cells into bare earth and object cells (ground and nonground cells).

The module uses concepts described by VOSSELMAN (2000) and is based on the assumption that a large height difference between two nearby cells is unlikely to be caused by a steep slope in the terrain. The probability that the higher cell could be a ground point decreases if the distance between the two cells decreases. Therefore the filter defines the acceptable height difference between two cells as a function of the distance between the cells. A cell is classified as terrain if there is no other cell within the kernel search radius such that the height difference between these cells is larger than the allowed maximum height difference at the distance between these cells.

The approximate terrain slope parameter is used to modify the filter function to match the overall slope in the study area. A confidence interval may be used to reject outliers.

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

Parameters

 NameTypeIdentifierDescriptionConstraints
InputGrid to filterGrid (input)INPUTThe grid to filter.-
OutputBare EarthGrid (output)GROUNDFiltered DTM-
Removed ObjectsGrid (output)NONGROUNDObjects removed from input grid-
OptionsSearch RadiusIntegerRADIUSSearch radius of kernel in cells.Minimum: 1
Default: 2
Approx. Terrain SlopeFloating pointTERRAINSLOPEApproximate Terrain Slope [%]Minimum: 0.000000
Default: 30.000000
Use Confidence IntervalBooleanSTDDEVUse 5 percent confidence intervalDefault: 0

Command-line

Usage: saga_cmd grid_filter 7 -INPUT <str> [-RADIUS <num>] [-TERRAINSLOPE <str>] [-STDDEV <str>] [-GROUND <str>] [-NONGROUND <str>]
  -INPUT:<str>       	Grid to filter
	Grid (input)
  -RADIUS:<num>      	Search Radius
	Integer
	Minimum: 1
	Default: 2
  -TERRAINSLOPE:<str>	Approx. Terrain Slope
	Floating point
	Minimum: 0.000000
	Default: 30.000000
  -STDDEV:<str>      	Use Confidence Interval
	Boolean
	Default: 0
  -GROUND:<str>      	Bare Earth
	Grid (output)
  -NONGROUND:<str>   	Removed Objects
	Grid (output)