Patrick J. Kennelly

An Online Social Networking Approach to Reinforce Learning of Rocks and Minerals

Numerous and varied methods are used in introductory Earth science and geology classes to help students learn about rocks and minerals, such as classroom lectures, laboratory specimen identification, and field trips. This paper reports on a method using online social networking. The choice of this forum was based on two criteria. First, many traditional students are likely comfortable with such an interface and its associated learning style. Second, social networking sites have functionality, such as the ability for users to link and group themselves, which is not available in other common web-facilitated learning environments such as course management systems. Each student was assigned the role of a unique mineral and rock. They were required to create a separate web page for each, with a photograph and description, on MySpace.com, a popular social networking web site. They were also required to join groups based on the classification of the rock or mineral. Finally, they were required to link to the minerals that constitute each rock by becoming “friends.” A post-exercise questionnaire showed all students found this a useful and enjoyable exercise, and most believed it helped them to learn and remember information about rocks and minerals.

A Uniform Sky Illumination Model to Enhance Shading of Terrain and Urban Areas

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.

Non-Photorealistic Rendering and Terrain Representation

In recent years, a branch of computer graphics termed non-photorealistic rendering (NPR) has defined its own niche in the computer graphics community. While photorealistic rendering attempts to render virtual objects into images that cannot be distinguished from a photograph, NPR looks at techniques designed to achieve other ends. Its goals can be as diverse as imitating an artistic style, mimicking a look comparable to images created with specific reproduction techniques, or adding highlights and details to images. In doing so, NPR has overlapped the study of cartography concerned with representing terrain in two ways. First, NPR has formulated several techniques that are similar or identical to antecedent terrain rendering techniques including inclined contours and hachures. Second, NPR efforts to highlight or add information in renderings often focus on the use of innovative and meaningful combinations of visual variables such as orientation and color. Such efforts are similar to recent terrain rendering research focused on methods to symbolize disparate areas of slope and aspect on shaded terrain representations. We compare these fields of study in an effort to increase awareness and foster collaboration between researchers with similar interests.

Hillshading of Terrain Using Layer Tints with Aspect-Variant Luminosity

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 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 maps are highlighted with this technique.

General sky models for illuminating terrains

Sky models are quantitative representations of natural luminance of the sky under various atmospheric conditions. They have been used extensively in studies of architectural design for nearly a century, and more recently for rendering objects in the field of computer graphics. The objectives of this paper are to (1) describe sky models, (2) demonstrate how map designers can render terrain under various sky models in a typical geographic information system (GIS), (3) illustrate potential enhancements to terrain renderings using sky models, and (4) discuss how sky models, with their well-established standards from a different discipline, might contribute to a virtual geographic environment (VGE). Current GIS hill-shading tools use the Lambertian assumption which can be related to a simple point light source at an infinite distance to render terrain. General sky models allow the map designer to choose from a gamut of sky models standardized by the International Commission on Illumination (CIE). We present a computer application that allows the map designer to select a general sky model and to use existing GIS tools to illuminate any terrain under that model. The application determines the orientations and weights of many discrete point light sources that, in the aggregate, approximate the illumination provided by the chosen sky model. We discuss specific enhancements to terrains that are shaded and shadowed with these general sky models, including additional detail of secondary landforms with soft shadows and more realistic shading contrasts. We also illustrate how non-directional illumination models result in renderings that lack the perceptual relief effect. Additionally, we argue that this process of creating hill-shaded visualizations of terrain with sky models shows parallels to other geo-simulations, and that basing such work on standards from the computer graphics industry shows potential for its use in VGE.

Illuminated Choropleth Maps

Choropleth maps are commonly used to show statistical variation among map enumeration units. Mapmakers take into account numerous considerations and make many decisions to produce a product that will effectively communicate spatially complex information to the map user. One design consideration is the choice between classed or unclassed choropleth maps. Unclassed maps assign a unique color, shade, or pattern based on each units value. These maps are rich in information but might not be optimal for visual discrimination of regions or identifying values from a legend. Classed maps classify enumeration units based on unit values and in some cases consider geographic area per class or contiguity. These classed maps better delineate regions and interclass variation but are designed to eliminate visibility of intraclass variations. We present a method designed to use colors for choropleth classes and soft shadows to show intraclass variations associated with adjacent or nearby polygons. We conceptualize the choropleth data as a three-dimensional prism model under simulated illumination, with the height of each enumeration unit a function of its mapped value. Our user studies have demonstrated that participants were able to use soft shadows to better identify which of two adjacent units was of greater population density, regardless of whether units were in the same or different classes. Additionally, the resulting soft shadows rarely interfere with the map readers ability to match color classes to a legend or to compare estimated differences in mean and variance of population density between two regions.

Modifications of Tanaka's Illuminated Contour Method

Visualization of topography can be greatly facilitated by the illuminated contour method. This method, popularized in a hand-drafted map by Tanaka, uses a gray background with black and white contours. A direction of illumination is assumed, and white contours represent illummated 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 Tanakas 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 hill 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.

GIS APPLICATIONS TO HISTORICAL CARTOGRAPHIC METHODS TO IMPROVE THE UNDERSTANDING AND VISUALIZATION OF CONTOURS

This article illustrates applications of Geographic Information System (GIS) technology to two alternative contouring methods published in English in 1932 and 1950 by the Japanese cartographer Kitiro Tanaka. Both of these methods have the potential to help students better understand and visualize contours. Inclined contour traces are defined by the intersection of topography with a series of evenly spaced, inclined planes, as opposed to the traditional horizontal planes used for most contours. This method has the potential to help students understand the concept of contour lines and profiles, aid students in the visualization of topography, and introduce students to the cartographic concept of analytical hillshading. Illuminated contours use black and white contours of varying thickness on a gray background to give the impression of an obliquely lit 3-dimensional surface. This method could help students visualize topography and introduce students to the concepts of aspect, slope and analytical hillshading.This article illustrates applications of Geographic Information System (GIS) technology to two alternative contouring methods published in English in 1932 and 1950 by the Japanese cartographer Kitiro Tanaka. Both of these methods have the potential to help students better understand and visualize contours. Inclined contour traces are defined by the intersection of topography with a series of evenly spaced, inclined planes, as opposed to the traditional horizontal planes used for most contours. This method has the potential to help students understand the concept of contour lines and profiles, aid students in the visualization of topography, and introduce students to the cartographic concept of analytical hillshading. Illuminated contours use black and white contours of varying thickness on a gray background to give the impression of an obliquely lit 3-dimensional surface. This method could help students visualize topography and introduce students to the concepts of aspect, slope and analytical hillshading.

Hillshading With Oriented Halftones

Hillshading renders a surface with a three-dimensional appearance using shades of gray. Although shades appear as continuous tones, they must undergo a halftoning process for use with most computer output devices. This process generally uses one pattern of black and white pixels for each shade of gray, while attempting to make patterns associated with black and white pixels as difficult to detect as possible. The method described in this paper adds aspect information to hillshaded maps with oriented halftones. Twelve orientations of clustered-dot ordered dithers represent 30° intervals of aspect. Additionally, dithering matches sixteen shades of gray associated with analytical hillshading, with each interval representing 16 of 256 shades of gray. This process allows pattern and gray tone representations of the surface simultaneously.

Cross-Hatched Shadow Line Maps

Abstract Cross-hatching is an artistic drawing method in which lines of variable thickness and orientation approximate tonal variations associated with shading and shadowing. Research in computer graphics has focused primarily on creating illustrations with cross-hatching that conforms to the three dimensional surface of virtual objects. Cross-hatched shadow maps apply cross-hatching to shadowed areas, with the length of these hatching lines based on the distance shadows are cast from point illumination sources at a number of discrete inclinations above the horizon. Thickness of lines increase within areas remaining shadowed at greater inclinations. By adding hatching lines from a second illumination azimuth, the resulting map is both cross-hatched and rendered with more diffuse shadows. The resulting map uses only shadows to represent terrain, a departure from other techniques such as hill-shading.