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A uniform sky illumination model to enhance shading of terrain and urban areas / Patrick Kennelly in Cartography and Geographic Information Science, vol 33 n° 1 (January 2006)
[article]
Titre : A uniform sky illumination model to enhance shading of terrain and urban areas Type de document : Article/Communication Auteurs : Patrick Kennelly, Auteur ; J. Stewart, Auteur Année de publication : 2006 Article en page(s) : pp 21 - 36 Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Cartographie numérique
[Termes IGN] correction des ombres
[Termes IGN] éclairement lumineux
[Termes IGN] estompage automatique
[Termes IGN] Nevada (Etats-Unis)
[Termes IGN] ombre
[Termes IGN] représentation des détails topographiques
[Termes IGN] système d'information géographique
[Termes IGN] Texas (Etats-Unis)
[Termes IGN] zone urbaineRésumé : (Auteur) 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. Copyright CaGISociety Numéro de notice : A2006-203 Affiliation des auteurs : non IGN Thématique : GEOMATIQUE Nature : Article DOI : 10.1559/152304006777323118 En ligne : https://doi.org/10.1559/152304006777323118 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=27930
in Cartography and Geographic Information Science > vol 33 n° 1 (January 2006) . - pp 21 - 36[article]Réservation
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