  I present a 3D advancing-front mesh refinement algorithm that generates a
constrained Delaunay mesh for any piecewise linear complex (PLC) and extend
this algorithm to produce truly Delaunay meshes for any PLC. First, as in my
recently published 2D algorithm, I split the input line segments such that the
length of the subsegments is asymptotically proportional to the local feature
size (LFS). For each facet, I refine the mesh such that the edge lengths and
the radius of the circumcircle of every triangular element are asymptotically
proportional to the LFS. Finally, I refine the volume mesh to produce a
constrained Delaunay mesh whose tetrahedral elements are well graded and have a
radius-edge ratio less than some $\omega^* > 2/\sqrt{3}$ (except ``near'' small
input angles). I extend this algorithm to generate truly Delaunay meshes by
ensuring that every triangular element on a facet satisfies Gabriel's
condition, i.e., its diametral sphere is empty. On an ``apex'' vertex where
multiple facets intersect, Gabriel's condition is satisfied by a modified
split-on-a-sphere (SOS) technique. On a line where multiple facets intersect,
Gabriel's condition is satisfied by mirroring meshes near the line of
intersection. The SOS technique ensures that the triangles on a facet near the
apex vertex have angles that are proportional to the angular feature size
(AFS), a term I define in the paper. All tetrahedra (except ``near'' small
input angles) are well graded and have a radius-edge ratio less than $\omega^*
> \sqrt{2}$ for a truly Delaunay mesh. The upper bounds for the radius-edge
ratio are an improvement by a factor of $\sqrt{2}$ over current
state-of-the-art algorithms.
