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

▶

Sep 06, 2022 383 likes •580 views

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

SLIDE 1

The Application & Effects of Sky Models on Hill Shading

Patrick Kennelly – LIU Post, Brookville, New York, USA James Stewart – Queens University, Kingston, Ontario, Canada

SLIDE 2

Hill Shading with Point Source Illumination

Elevation Grid Hill Shaded Grid

Background Objectives Methodology Results Summary

SLIDE 3

Point Source Illumination

Background Objectives Methodology Results Summary

SLIDE 4

Point Source Illumination

Background Objectives Methodology Results Summary

SLIDE 5

CIE Sky Models

 Non-Directional

 Uniform  Overcast

 Directional

 Clear  Sharp  Turbid  General (1 – 15)

Background Objectives Methodology Results Summary

SLIDE 6

CIE Sky Models

Background Objectives Methodology Results Summary

Directional Non-Directional

Uniform Overcast Sky Point Source Sharp + Uniform Sharp Clear Day

✔ ✔ ✔

SLIDE 7

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

f terrain or landforms.

Background Objectives Methodology Results Summary

SLIDE 8

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

SLIDE 9

Methodology

Background Objectives Methodology Results Summary x W1 x W2 x W3 x W4 x W5 + + + + +

SLIDE 10

Mt. Hood, OR

Point Source Clear Day

Background Objectives Methodology Results Summary

SLIDE 11

Mt. Hood, Oregon

Point Source Clear Day

Background Objectives Methodology Results Summary

SLIDE 12

Mt. Hood, Oregon

Background Objectives Methodology Results Summary

Clear Point

Aspect

m=-0.5072 R2=0.69441 m=-1.0026 R2=0.36791

SLIDE 13

Mt. Hood, Oregon

Point Source Overcast Sky

Background Objectives Methodology Results Summary

SLIDE 14

Grand Canyon, Arizona

Point Source Clear Day

Background Objectives Methodology Results Summary

SLIDE 15

Grand Canyon, Arizona

Background Objectives Methodology Results Summary

Elevation

m=-0.6517 R2=0.00189 m=9.7655 R2=0.05161

SLIDE 16

Grand Canyon, Arizona

Point Source Overcast Sky

Background Objectives Methodology Results Summary

SLIDE 17

Grand Canyon, AZ

Point Source Overcast Sky

Background Objectives Methodology Results Summary

SLIDE 18

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

SLIDE 19

Beta Application Download

 PC Application plus Python script (etc.)  http://watkins.cs.queensu.ca/~jstewart/SkyLum.zip

Background Objectives Methodology Results Summary