1. A method of determining the visibility of surfaces of three-dimensional objects, projected on a view plane from data defining said surfaces of three- dimensional objects, said method comprising: a) deriving data indicative of boundaries of projections of said surfaces on said view plane, b) determining a finite number of subdivisions of said view plane thereby providing perimeters of each of said subdivisions, c) determining points of intersection of said perimeter of one of said subdivisions with said boundaries of said surfaces projected on said view plane; d) determining the distribution of surfaces visible along said perimeter of said of one of said subdivisions by utilizing said points of intersection, and e) determining if said one subdivision is terminal from at least said distribution of surfaces visible along said perimeter of said one subdivision.