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Elevation models for reproducible evaluation of terrain representation / Patrick Kennelly in Cartography and Geographic Information Science, vol 48 n° 1 (January 2021)  

Public [article]  inCartography and Geographic Information Science > vol 48 n° 1 (January 2021) . - pp 63 - 77 Titre : Elevation models for reproducible evaluation of terrain representation Type de document : Article/Communication Auteurs : Patrick Kennelly, Auteur ; Tom Patterson, Auteur ; Bernhard Jenny, Auteur ; et al., Auteur Année de publication : 2021 Article en page(s) : pp 63 - 77 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Photogrammétrie numérique [Termes IGN] altitude [Termes IGN] données multiéchelles [Termes IGN] figuré du terrain [Termes IGN] modèle numérique de surface [Termes IGN] réalité de terrain [Termes IGN] relief [Termes IGN] représentation du relief [Termes IGN] reproductibilité [Termes IGN] visualisation de données Résumé : (auteur) This paper proposes elevation models to promote, evaluate, and compare various terrain representation techniques. Our goal is to increase the reproducibility of terrain rendering algorithms and techniques across different scales and landscapes. We introduce elevation models of varying terrain types, available to the user at no cost, with minimal common data imperfections such as missing data values, resampling artifacts, and seams. Three multiscale elevation models are available, each consisting of a set of elevation grids, centered on the same geographic location, with increasing cell sizes and spatial extents. We also propose a collection of single-scale elevation models of archetypal landforms including folded ridges, a braided riverbed, active and stabilized sand dunes, and a volcanic caldera. An inventory of 78 publications with a total of 155 renderings illustrating terrain visualization techniques guided the selection of landform types in the elevation models. The benefits of using the proposed elevation models include straightforward comparison of terrain representation methods across different publications and better documentation of the source data, which increases the reproducibility of terrain representations. Numéro de notice : A2021-715 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1080/15230406.2020.1830856 date de publication en ligne : 04/11/2020 En ligne : https://doi.org/10.1080/15230406.2020.1830856 Format de la ressource électronique : url article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=96459 [article]

Cartographic symbol design considerations for the space–time cube / Christopher League in Cartographic journal (the), Vol 56 n° 2 (May 2019)  

Public [article]  inCartographic journal (the) > Vol 56 n° 2 (May 2019) . - pp 117 - 133 Titre : Cartographic symbol design considerations for the space–time cube Type de document : Article/Communication Auteurs : Christopher League, Auteur ; Patrick Kennelly, Auteur Année de publication : 2019 Article en page(s) : pp 117 - 133 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Termes IGN] conception cartographique [Termes IGN] cube espace-temps [Termes IGN] données localisées 2D [Termes IGN] données spatiotemporelles [Termes IGN] figuré ponctuel [Termes IGN] saturation de la couleur [Termes IGN] sémiologie graphique [Termes IGN] symbole graphique 3D [Vedettes matières IGN] Géovisualisation Résumé : (Auteur) The cartographic representation of geographic phenomena in the space–time cube comes with special challenges and opportunities when compared with two-dimensional maps. While the added dimension allows the display of attributes that vary with time, it is difficult to display rapidly varying temporal data given the limited display height. In this study, we adapt 2D cyclic point symbols to construct 3D surfaces designed along a helical path for the space–time cube. We demonstrate how these complex 3D helical surfaces can display detailed data, including data reported daily over 100 years and data reported in four-hour intervals over a year. To create the point symbols, each value is plotted along the curve of a helix, with each turn of the helix representing one year or week, respectively. The model is modified by varying the radii from the time axis to all points using the attribute value, in these cases maximum daily temperature and four-hourly ridership, and then creating a triangulated surface from the resulting points. Using techniques common to terrain representation, we apply hue and saturation to the surface based on attribute values, and lightness based on relief shading. Multiple surfaces can be displayed in a space–time cube with a consistent time interval facing the viewer, and the surfaces or viewer perspective can be rotated to display synchronized variations. We see this method as one example of how cartographic design can refine or enhance operations in the space–time cube. Numéro de notice : A2019-239 Affiliation des auteurs : non IGN Thématique : GEOMATIQUE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1080/00087041.2018.1533291 date de publication en ligne : 29/05/2019 En ligne : https://doi.org/10.1080/00087041.2018.1533291 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=92931 [article]

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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)  

Public [article]  inCartography and Geographic Information Science > vol 33 n° 1 (January 2006) . - pp 21 - 36 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 urbaine Résumé : (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 [article]

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Hillshading of terrain using layer tints with aspect-variant luminosity / Patrick Kennelly in Cartography and Geographic Information Science, vol 31 n° 2 (April 2004)  

Public [article]  inCartography and Geographic Information Science > vol 31 n° 2 (April 2004) . - pp 67 - 77 Titre : Hillshading of terrain using layer tints with aspect-variant luminosity Type de document : Article/Communication Auteurs : Patrick Kennelly, Auteur ; A.J. Kimerling, Auteur Année de publication : 2004 Article en page(s) : pp 67 - 77 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Cartographie numérique [Termes IGN] éclairement lumineux [Termes IGN] estompage [Termes IGN] luminance lumineuse [Termes IGN] transformation intensité-teinte-saturation Résumé : (Auteur) Hillshading provides a rendering of topographic surfaces by assigning brightness to surface elements based on the orientation of these elements and a selected direction of illumination. Users easily visualize many topographic features, but some areas lack detail, as one shade of gray does not define a unique surface orientation. We clarify some of this ambiguity by varying the color of layer tints with aspect direction. We use the CIELAB [commission internationale de l'éclairage] color model to quantify color specifications and map variations in luminosity onto slices of the Hue-Saturation-Value (HSV) color model. Traditionally, cartographers assign an aspect-invariant color (or colors) based on H and S and vary V with the hillshading values. In our research, we assign aspect-variant H and V values in close proximity in HSV color space. We use values of luminosity and saturation from the CIELAB and HSV color models to select colors that are least saturated, most saturated, least luminous, and most luminous to represent the northwest, southeast, southwest, and northeast directions, respectively. We then vary V in the traditional manner with hillshading from the northwest. Topographic details not apparent in the original hillshaded mas are highlighted with this technique. Numéro de notice : A2004-340 Affiliation des auteurs : non IGN Thématique : GEOMATIQUE Nature : Article DOI : 10.1559/1523040041649416 En ligne : https://doi.org/10.1559/1523040041649416 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=26867 [article]

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Modifications of Tanaka's illuminated contour method / Patrick Kennelly in Cartography and Geographic Information Science, vol 28 n° 2 (April 2001)  

Public [article]  inCartography and Geographic Information Science > vol 28 n° 2 (April 2001) . - pp 111 - 123 Titre : Modifications of Tanaka's illuminated contour method Type de document : Article/Communication Auteurs : Patrick Kennelly, Auteur ; A.J. Kimerling, Auteur Année de publication : 2001 Article en page(s) : pp 111 - 123 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Cartographie numérique [Termes IGN] carte des pentes [Termes IGN] contour [Termes IGN] éclairement lumineux [Termes IGN] niveau de gris (image) [Termes IGN] représentation du relief [Termes IGN] visualisation cartographique Résumé : (Auteur) Visualization of topography can be greatly facilitated by the illuminated contour method. This method, popularized in a hand-drafted map byTanaka, uses a gray background with black and white contours. A direction of illumination is assumed, and white contours represent illuminated topography, while black contours represent non-illuminated or shaded areas. Additionally, thickness of contours varies with the cosine of the angle between the azimuth of maximum slope (i.e., aspect) and the azimuth of illumination. We modified Tanaka's method by basing thickness of contour lines on twice the cosine of the angle between the surface normal and the illumination vector. The cosine of this angle is most commonly used in analytical bill shading. In addition, we present maps with changes in other visual variables and offer our evaluations. Lines with gray tones instead of black and white lines do not improve the illumination effect. We believe variations in the colors of contours and background with elevation can visually enforce information regarding topography. Our use of colors for aspect and variations in the width of contours for slope adds information to the map but does not assist with visualization of topography. Numéro de notice : A2001-100 Affiliation des auteurs : non IGN Thématique : GEOMATIQUE Nature : Article DOI : 10.1559/152304001782173709 En ligne : https://doi.org/10.1559/152304001782173709 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=21800 [article]

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