Visible surface algorithms for quadric patches

This paper describes two algorithms which find the visible portions of surfaces in a picture of a cluster of three-dimensional quadric patches. A quadric patch is a portion of quadric surface defined by a quadratic equation and by zero, one or several quadratic inequalities. The picture is cut by parallel planes called scan planes; the visibility problem is solved in one scan plane at a time by making "a good guess" as t o what is visible according to the visible portions found in the previous can plane. The algorithm for intersecting patches works in a time roughly proportional to the number of patches involved (and not to the square of this number as with some previous algorithms).