Abstract: A method for grouping primitives into pairs of adjoining triangles for use in a ray tracing process. An input list of edges of triangular primitives is obtained, an edge bounding volume surface area (BVSA) and an additional edge qualifier is determined for each of the edges. The entries in the input list are sorted by edge BVSA then by edge qualifier, giving a sorted list in which the entries have a sorted order. The list is traversed in the sorted order to seek groups of matched edges within a predetermined window of list entries, each edge in a matched group having a matching edge BVSA and edge qualifier with another edge in the matched group from a different triangular primitive. When a group of matched edges is found, associated triangular primitives are designated as a cluster of adjoining primitives. The cluster of adjoining primitives are processed together as a group.