Tool Name	Analytical Hillshading
Tool ID	0
Library ID	ta_lighting
Version	1.0
Author(s)	O.Conrad, V.Wichmann (c) 2003-2025

Description

This tool performs an analytical hillshade computation for an elevation grid. The 'Standard' method simply calculates the angle at which light coming from the position of the light source would hit the surface. This method can produce angles greater than 90 degree. With the second method all values are kept within the range of 0-90 degree. It can be enhanced with shadowing effects, where shadowed cells will be marked with a value of exactly 90 degree. 'Shadows Only' creates a mask for the shadowed areas and sets all other cells to no-data. 'Combined Shading' takes the values of the standard method and multiplies these with the normalized slope. 'Ambient Occlusion' is based on the concepts of Tarini et al. (2006). 'Multidirectional' combines standard shadings computed for six different lighting directions to show more detail. The 'Multidirectional (USGS)' method combines four aspect weighted lighting directions.

References

Mark, R. (1992): Multidirectional, oblique-weighted, shaded-relief image of the Island of Hawaii. U.S. Geological Survey, Open-File Report 92-422. PDF

Tarini, M., Cignoni, P., Montani, C. (2006): Ambient Occlusion and Edge Cueing to Enhance Real Time Molecular Visualization. IEEE Transactions on Visualization and Computer Graphics, Vol. 12, No. 5, pp. 1237-1244. doi:10.1109/tvcg.2006.115

Parameters

Name	Type	Identifier	Description	Constraints
Input
Elevation	grid, input	ELEVATION
Output
Analytical Hillshading	grid, output	SHADE	The angle between the surface and the incoming light beams, measured in radians.
Options
Shading Method	choice	METHOD		Available Choices: [0] Standard [1] Limited Maximum [2] With Shadows [3] Shadows Only [4] Ambient Occlusion [5] Combined Shading [6] Multidirectional [7] Multidirectional (USGS) Default: 0
Sun's Position	choice	POSITION		Available Choices: [0] azimuth and height [1] date and time Default: 0
Azimuth	floating point number	AZIMUTH	Direction of the light source, measured in degree clockwise from the North direction.	Minimum: 0.000000 Maximum: 360.000000 Default: 315.000000
Height	floating point number	DECLINATION	Height of the light source, measured in degree above the horizon.	Minimum: 0.000000 Maximum: 90.000000 Default: 45.000000
Day	date	DATE		Default: 2026-07-17
Hour	floating point number	TIME		Minimum: 0.000000 Maximum: 24.000000 Default: 12.000000
Exaggeration	floating point number	EXAGGERATION	The terrain exaggeration factor allows one to increase the shading contrasts in flat areas.	Default: 1.000000
Unit	choice	UNIT		Available Choices: [0] radians [1] degree Default: 0
Shadow	choice	SHADOW	Choose 'slim' to trace grid node's shadow, 'fat' to trace the whole cell's shadow. The first is slightly faster but might show some artifacts.	Available Choices: [0] slim [1] fat Default: 1
Sampling Hemisphere	choice	SAMPLING	Choose which hemisphere of the ambient-occlusion sampling sphere is used.	Available Choices: [0] north [1] south [2] full Default: 0
Number of Directions	integer number	NDIRS	Number of sample directions for ambient occlusion. Divides azimuth range of hemisphere into sectors. Declination (0 to 90 degree) is divided in (Number of Directions / 4) sectors.	Minimum: 2 Default: 8
Search Radius	floating point number	RADIUS	Radius used to trace for shadows (ambient occlusion) [map units].	Minimum: 0.001000 Default: 10.000000
Radius Smoothing	integer number	KERNEL_RADIUS	The kernel radius used for DEM smoothing [cells].	Minimum: 0 Default: 3