The Application & Effects of Sky Models on Hill Shading Patrick - PowerPoint PPT Presentation

The Application & Effects of Sky Models on Hill Shading Patrick Kennelly – LIU Post, Brookville, New York, USA James Stewart – Queens University, Kingston, Ontario, Canada

Hill Shading with Point Source Illumination Elevation Grid Hill Shaded Grid Background Objectives Methodology Results Summary

Point Source Illumination Background Objectives Methodology Results Summary

Point Source Illumination Background Objectives Methodology Results Summary

CIE Sky Models Non-Directional  Uniform  Overcast  Directional  Clear  Sharp  Turbid  General (1 – 15)  Background Objectives Methodology Results Summary

CIE Sky Models Directional Non-Directional ✔ ✔ Point Source Clear Day Uniform ✔ Sharp Sharp + Uniform Overcast Sky Background Objectives Methodology Results Summary

Objectives  Use CIE sky models to create shaded and shadowed terrain representations.  Understand the distribution of shades of gray with respect to slope, aspect, and elevation.  Understand which sky models create useful effects for illuminating various types of terrain or landforms. Background Objectives Methodology Results Summary

Methodology Begin with large number of sky sample points of equal  azimuth spacing for equal increments of inclination. Sky radiance for each sample point is computed.  Radiance values of sample points are divided into a  given number of standard deviations, each representing a strata. Each stratum allocated approximately the same  number of illumination vectors. Illumination vectors iteratively chosen to maximize  angular distance from all previously chosen directions. Background Objectives Methodology Results Summary

Methodology x x x x x W 1 W 2 W 3 W 4 W 5 + + + + + Background Objectives Methodology Results Summary

Mt. Hood, OR Point Source Clear Day Background Objectives Methodology Results Summary

Mt. Hood, Oregon Point Source Clear Day Background Objectives Methodology Results Summary

Mt. Hood, Oregon Aspect m=-0.5072 R 2 =0.69441 Point m=-1.0026 R 2 =0.36791 Clear Background Objectives Methodology Results Summary

Mt. Hood, Oregon Point Source Overcast Sky Background Objectives Methodology Results Summary

Grand Canyon, Arizona Point Source Clear Day Background Objectives Methodology Results Summary

Grand Canyon, Arizona Elevation m=-0.6517 R 2 =0.00189 m=9.7655 R 2 =0.05161 Background Objectives Methodology Results Summary

Grand Canyon, Arizona Point Source Overcast Sky Background Objectives Methodology Results Summary

Grand Canyon, AZ Point Source Overcast Sky Background Objectives Methodology Results Summary

Summary CIE sky models can be rigorously implemented to hill shade  terrain. Sky model illumination can reveals details of terrain that can  be lost in weakly or strongly illuminated terrain. Directional sky models preserve the three-dimensional  appearance of terrain with predominantly positive relief while more evenly distributing shades of gray with aspect. Non-directional sky models permit more light to illuminate  the depths of dissected terrain, allowing for enhanced rendering of landforms such as canyon floors. Background Objectives Methodology Results Summary

Beta Application Download PC Application plus Python script (etc.)  http://watkins.cs.queensu.ca/~jstewart/SkyLum.zip  Background Objectives Methodology Results Summary