Abstract: The lines representing each edge of each face of each object of a model for producing a multiple object image are segmented at line of sight intersections with other lines representing contour edges of visible faces. Each resulting edge line segment is checked against all visible faces to determine which are visible and which are invisible, and information on visibility is stored together with detailed information on each edge line segment for each object. The model is modified by changing the number of component objects and after each change checking the edge line segments for visibility only with respect to the changes associated with the changed component objects. This results in a substantial reduction in the required number of comparisons between segments and faces as compared to prior methods.

Abstract: A projection screen of improved aesthetic quality. The screen comprises a plurality of rectilinear rows of precisely contoured optical microelements each adapted to redistribute substantially all of the incident image flux through a predefined audience angle with uniform luminance. The microelements are formed in a surface of a work piece by applying an electrical signal of predefined waveform but of random frequency to the input of the cutting stylus of a sound recording head which moves relative to the work piece in a series of parallel traverses. The electrical signal is recorded on a memory element which moves with the work piece past a stationary pickup head as each row is cut. Because the same signal from the memory element is used to cut each row, an identical phase relationship is maintained between the microelements in adjacent rows.