Abstract: A method of simulating the appearance of smoke in an electronically generated video image that uses one or more intersecting opaque spheres. Each sphere has a nonuniform smoke density that produces feathered edges. The smoke sphere is an object modeled as a center point (the coordinates of the center of the sphere in three dimensions), a radius (in database coordinates), and a set of parameters that include density and color. The center point is transformed into display screen coordinates, and the radius is transformed into a screen coordinate length. The sphere is projected into a circle in screen coordinates, and a bounding square is generated in screen coordinates that is centered at the sphere center point. The bounding square is then converted into a transparency having color and density attributes added to its data structure. Thus the bounding square has the same data structure as transparent or opaque objects and is processed in the same manner.

Abstract: A locomotion simulator has two independently controlled movable footpads. Each footpad is positioned dynamically in three-dimensions. The top of each footpad has a controlled rotational motion, and the assembly having the two footpads is rotated under control. In operation, a user, whose feet are tracked in position and angle, walks or runs on the simulator and the footpads are controlled to simulate ground contact. Controlled rotation and translation movements permit simulation of turning, climbing, and decending.

Abstract: A method for determining which objects are visible in each pixel of a digitally-generated image is described. The method uses comparison of distances from the viewpoint (Z-sorting) for occlusion. The number of Z comparisons required is minimized by utilizing a hierarchy of regions in the screen area, and thereby, resolving occlusion for areas larger than pixel areas where possible. Use of the area hierarchy increases the efficiency of the occlusion processing. In a preferred implementation, the screen is divided into equal-sized horizontal regions each corresponding to typically four scanlines. Polygons for each image are subdivided into pieces that correspond to the preset hierarchy of regions, and occlusion processing occurs independently in parallel for two or more regions. Each region is subdivided further into smaller regions, each level of the hierarchy having regions half the size of a higher level region.

Abstract: The specification describes a way of using distance sorting in order not to require a prioritization of those polygons that are to be rendered prior to a pixel-by-pixel construction of an image. The video processor recalls the input data into the pixel processor at least a number of times equal to the number of objects to be displayed.

Abstract: A logarithmic mixer circuit in the form of a conversion circuit for mixing digital representations of logarithmic values eliminating the usual mathematical processes of determining anti-logs, summing them and then determining the logs again, the invention using addition, subtraction and a look up table. Additional utiity is obtained by the use of scaled offset representations of logarithmic values for digital processing and separate representations for zero values. Also the final output values are limited to the range of the inputs in anticipation of further processing.

Abstract: An airborne positioning system for acquiring range information from at least three distance measuring equipment (DME) stations, including a computer controlled range gate and means for estimating and removing bias errors from range measurements and smoothing noise to accurately determined aircraft position to typically better than 100 feet circular error probable (C.E.P.).