A uniform sky illumination model to enhance shading of terrain and urban areas

Patrick Joseph Kennelly, A. James Stewart

Research output: Contribution to journalArticle

14 Citations (Scopus)

Abstract

Users of geographic information systems (GIS) usually render terrain using a point light source defined by an illumination vector. A terrain shaded from a single point provides good perceptual cues to surface orientation. This type of hill shading, however, does not include any visual cues to the relative height of surface elements. We propose shading the terrain under uniform diffuse illumination, where light arrives equally from all directions of a theoretical sky surrounding the terrain. Surface elements at lower elevations tend to have more of the sky obscured from view and are thus shaded darker. This tinting approach has the advantage that it provides more detailed renderings than point source illumination. We describe two techniques of computing terrain shading under uniform diffuse illumination. One technique uses a GIS-based hill-shading and shadowing tool to combine many point source renderings into one approximating the terrain under uniform diffuse illumination. The second technique uses a C+ + computer algorithm for computing the inclination to the horizon in all azimuth directions at all points of the terrain. These virtual horizons are used to map sky brightness to the rendering of the terrain. To evaluate our techniques, we use two Digital Elevation Models (DEMs) - of the Schell Creek Range of eastern Nevada and a portion of downtown Houston, Texas, developed from Light Detection and Ranging (lidar) data. Renderings based on the uniform diffuse illumination model show more detailed changes in shading than renderings based on a point source illumination model.

Original languageEnglish (US)
Pages (from-to)21-36
Number of pages16
JournalCartography and Geographic Information Science
Volume33
Issue number1
DOIs
StatePublished - Jan 1 2006

Fingerprint

shading
urban area
Lighting
information system
point source
city center
Geographic information systems
visual cue
Urban areas
Light sources
Luminance
azimuth
digital elevation model

All Science Journal Classification (ASJC) codes

  • Civil and Structural Engineering
  • Geography, Planning and Development
  • Management of Technology and Innovation

Cite this

@article{8858ce6338854e048a5ad8d243eb7eab,
title = "A uniform sky illumination model to enhance shading of terrain and urban areas",
abstract = "Users of geographic information systems (GIS) usually render terrain using a point light source defined by an illumination vector. A terrain shaded from a single point provides good perceptual cues to surface orientation. This type of hill shading, however, does not include any visual cues to the relative height of surface elements. We propose shading the terrain under uniform diffuse illumination, where light arrives equally from all directions of a theoretical sky surrounding the terrain. Surface elements at lower elevations tend to have more of the sky obscured from view and are thus shaded darker. This tinting approach has the advantage that it provides more detailed renderings than point source illumination. We describe two techniques of computing terrain shading under uniform diffuse illumination. One technique uses a GIS-based hill-shading and shadowing tool to combine many point source renderings into one approximating the terrain under uniform diffuse illumination. The second technique uses a C+ + computer algorithm for computing the inclination to the horizon in all azimuth directions at all points of the terrain. These virtual horizons are used to map sky brightness to the rendering of the terrain. To evaluate our techniques, we use two Digital Elevation Models (DEMs) - of the Schell Creek Range of eastern Nevada and a portion of downtown Houston, Texas, developed from Light Detection and Ranging (lidar) data. Renderings based on the uniform diffuse illumination model show more detailed changes in shading than renderings based on a point source illumination model.",
author = "Kennelly, {Patrick Joseph} and Stewart, {A. James}",
year = "2006",
month = "1",
day = "1",
doi = "10.1559/152304006777323118",
language = "English (US)",
volume = "33",
pages = "21--36",
journal = "Cartography and Geographic Information Science",
issn = "1523-0406",
publisher = "American Congress on Surveying and Mapping",
number = "1",

}

A uniform sky illumination model to enhance shading of terrain and urban areas. / Kennelly, Patrick Joseph; Stewart, A. James.

In: Cartography and Geographic Information Science, Vol. 33, No. 1, 01.01.2006, p. 21-36.

Research output: Contribution to journalArticle

TY - JOUR

T1 - A uniform sky illumination model to enhance shading of terrain and urban areas

AU - Kennelly, Patrick Joseph

AU - Stewart, A. James

PY - 2006/1/1

Y1 - 2006/1/1

N2 - Users of geographic information systems (GIS) usually render terrain using a point light source defined by an illumination vector. A terrain shaded from a single point provides good perceptual cues to surface orientation. This type of hill shading, however, does not include any visual cues to the relative height of surface elements. We propose shading the terrain under uniform diffuse illumination, where light arrives equally from all directions of a theoretical sky surrounding the terrain. Surface elements at lower elevations tend to have more of the sky obscured from view and are thus shaded darker. This tinting approach has the advantage that it provides more detailed renderings than point source illumination. We describe two techniques of computing terrain shading under uniform diffuse illumination. One technique uses a GIS-based hill-shading and shadowing tool to combine many point source renderings into one approximating the terrain under uniform diffuse illumination. The second technique uses a C+ + computer algorithm for computing the inclination to the horizon in all azimuth directions at all points of the terrain. These virtual horizons are used to map sky brightness to the rendering of the terrain. To evaluate our techniques, we use two Digital Elevation Models (DEMs) - of the Schell Creek Range of eastern Nevada and a portion of downtown Houston, Texas, developed from Light Detection and Ranging (lidar) data. Renderings based on the uniform diffuse illumination model show more detailed changes in shading than renderings based on a point source illumination model.

AB - Users of geographic information systems (GIS) usually render terrain using a point light source defined by an illumination vector. A terrain shaded from a single point provides good perceptual cues to surface orientation. This type of hill shading, however, does not include any visual cues to the relative height of surface elements. We propose shading the terrain under uniform diffuse illumination, where light arrives equally from all directions of a theoretical sky surrounding the terrain. Surface elements at lower elevations tend to have more of the sky obscured from view and are thus shaded darker. This tinting approach has the advantage that it provides more detailed renderings than point source illumination. We describe two techniques of computing terrain shading under uniform diffuse illumination. One technique uses a GIS-based hill-shading and shadowing tool to combine many point source renderings into one approximating the terrain under uniform diffuse illumination. The second technique uses a C+ + computer algorithm for computing the inclination to the horizon in all azimuth directions at all points of the terrain. These virtual horizons are used to map sky brightness to the rendering of the terrain. To evaluate our techniques, we use two Digital Elevation Models (DEMs) - of the Schell Creek Range of eastern Nevada and a portion of downtown Houston, Texas, developed from Light Detection and Ranging (lidar) data. Renderings based on the uniform diffuse illumination model show more detailed changes in shading than renderings based on a point source illumination model.

UR - http://www.scopus.com/inward/record.url?scp=33645290488&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=33645290488&partnerID=8YFLogxK

U2 - 10.1559/152304006777323118

DO - 10.1559/152304006777323118

M3 - Article

VL - 33

SP - 21

EP - 36

JO - Cartography and Geographic Information Science

JF - Cartography and Geographic Information Science

SN - 1523-0406

IS - 1

ER -