A computer-implemented method of determining a set of mesh polygons or fragments of said mesh polygons visible from a view region having a plurality of view region vertices, said mesh polygons forming polygon meshes, the method for use in 3D rendering and comprising steps of: a) determining an edge of at least one of said polygon meshes and determining at least one supporting polygon between said view region and the at least one edge; b) constructing at least one wedge based on said at least one supporting polygon, said at least one wedge defined in a supporting plane in which supporting plane the supporting polygon lies, and extending away from said view region beyond at least said one polygon mesh; c) determining intersections of plural such wedges with each other and with at least one other of said mesh polygons, the intersections together forming a polyhedral aggregate umbrae, PAU, the said PAU being the volume of space occluded by a mesh object from the view region; and d) determining whether or not said set of said mesh polygons or fragments of said mesh polygons is visible from said view region, wherein the set of said mesh polygons or fragments of said mesh polygons is visible if the set of said mesh polygons or fragments of said mesh polygons is outside said PAU; wherein the determining a) of the edge includes determining the edge to be only a first-order silhouette edge of the at least one of said polygon meshes, wherein said at least one supporting polygon is determined between said view region and at least one vertex of said at least one first-order silhouette edge, and wherein the determined edge is a first-order silhouette edge if the following conditions are met: i) first and second polygons of said set of mesh polygons or fragments thereof sharing said at least one first-order silhouette edge, ii) the first polygon backfacing (315,320) relative to each view region vertex from the plurality of view region vertices, wherein the backfacing implies that the plurality of view region vertices are in a different half-space from the half-space pointed to by the normal vector of the plane of the first polygon in which plane the first polygon lies; iii) the second polygon front-facing (325,340) to at least one view region vertex from the plurality of view region vertices, wherein the front-facing implies that at least one of the view region vertices is in the same half-space pointed to by the normal vector of the plane of the second polygon in which plane the second polygon lies, and iv) the first and second polygons having a backfacing (330,345) orientation with respect to each other, wherein at least one of the first and second polygons has a backfacing orientation with respect to a vertex of the at least one other of the first and second polygons, wherein said vertex is not a vertex of the shared first-order silhouette edge. a) determining an edge of at least one of said polygon meshes and determining at least one supporting polygon between said view region and the at least one edge; b) constructing at least one wedge based on said at least one supporting polygon, said at least one wedge defined in a supporting plane in which supporting plane the supporting polygon lies, and extending away from said view region beyond at least said one polygon mesh; c) determining intersections of plural such wedges with each other and with at least one other of said mesh polygons, the intersections together forming a polyhedral aggregate umbrae, PAU, the said PAU being the volume of space occluded by a mesh object from the view region; and d) determining whether or not said set of said mesh polygons or fragments of said mesh polygons is visible from said view region, wherein the set of said mesh polygons or fragments of said mesh polygons is visible if the set of said mesh polygons or fragments of said mesh polygons is outside said PAU; wherein the determining a) of the edge includes determining the edge to be only a first-order silhouette edge of the at least one of said polygon meshes, wherein said at least one supporting polygon is determined between said view region and at least one vertex of said at least one first-order silhouette edge, i) first and second polygons of said set of mesh polygons or fragments thereof sharing said at least one first-order silhouette edge, ii) the first polygon backfacing (315,320) relative to each view region vertex from the plurality of view region vertices, wherein the backfacing implies that the plurality of view region vertices are in a different half-space from the half-space pointed to by the normal vector of the plane of the first polygon in which plane the first polygon lies; iii) the second polygon front-facing (325,340) to at least one view region vertex from the plurality of view region vertices, wherein the front-facing implies that at least one of the view region vertices is in the same half-space pointed to by the normal vector of the plane of the second polygon in which plane the second polygon lies, and iv) the first and second polygons having a backfacing (330,345) orientation with respect to each other, wherein at least one of the first and second polygons has a backfacing orientation with respect to a vertex of the at least one other of the first and second polygons, wherein said vertex is not a vertex of the shared first-order silhouette edge.