A combined octant/Delaunay method for fully automatic 3D mesh generation with multiple level octant differences
Roger T. Marchand, S.M. Riad, Aicha Elshabini-Riad · Communications in Numerical Methods in Engineering · 1996
Automated mesh generation using a combined octree/Delaunay approach typically requires that rectangular elements be bounded by other rectangular elements which are not more that one division smaller (i.e. 1/8 the volume in 3D). This limitation is sometimes referred to as the 2 : 1 rule. This paper presents a modification which allows for any level of difference.