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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. KEYWORDS: Illumination model, point source illumination, uniform diffuse illumination, shading, shadowing, Introduction Illumination models are important in computer graphics to create realistic surface renderings. These models consist of a source of illuminating light and an illuminated surface, and they can include [...]

In this paper, the design and implementation of a high-speed 'CSG renderer' for displaying convex and concave objects and its performance analysis are presented. The renderer comprises a binary tree-structured depth generator that produces the depth values of a plane at each pixel on the display window simultaneously, and pipelined pixel processors that processes the depth values, a corner bender, and a frame-buffer. In this work, constructive solid geometry (CSG) scene models are used to simplify the hidden area removal and object interference testing. The field programmable gate array technology is used in the implementation. Keywords: CSG, Computer graphics; FPGA; Z-buffer