310 likes | 317 Vues
Tamal K. Dey Joshua A. Levine Andrew G. Slatton The Ohio State University. Localized Delaunay Refinement for Sampling and Meshing. Restricted Delaunay. Del S| M : Collection of Delaunay simplices t where V t intersects M. Delaunay Refinement. Input surface M Check conditions
E N D
Tamal K. Dey Joshua A. Levine Andrew G. Slatton The Ohio State University Localized Delaunay Refinement for Sampling and Meshing
Restricted Delaunay • Del S|M: Collection of Delaunay simplices t where Vt intersects M
Delaunay Refinement • Input surface M • Check conditions • If violated, insert • Vt∩M into S • Output: Del S|M
Existing Methods Check surface Delaunay ball size [BO05] Check topological disk [CDRR06]
Limitations Traditional refinement maintains Delaunay triangulation in memory This does not scale well Causes memory thrashing May be aborted by OS
Our Contribution A simple algorithm that avoids the scaling issues of the Delaunay triangulation Avoids memory thrashing Topological and geometric guarantees Guarantee of termination Potentially parallelizable
A Natural Solution Use an octree T to divide S and process points in each node v of T separately
Two Concerns • Termination • Mesh consistency
Termination Trouble A locally furthest point in node v can be very close to a point in other nodes
Messing Mesh Consistency Individual meshes do not blend consistently across boundaries
LocDel Algorithm: Overview Process nodes from a queue Q Refines nodes with parameter λ if there are violations
Splitting and reprocessing Split Let S = ∩ S Split into eight children if ||S||> Reprocess
Refining node Augment Assemble R=NUS Compute Del R|M Refine Surface Delaunay ball larger than λ Fp Del R|M is not a disk
Returned points for violations Checking Violations Large triangle t incident to p ϵ S Radius of surface ball > λ Return (p,p*) where p* is furthest dual(t) ∩ M Non-disk surface star Fp Return (p,p*) where p* is the furthest dual(t) ∩ M among all triangles
Point Insertions Modified insertion strategy If nearest point s ϵ S to p* is within λ/8 and s ≠ p, then add s to R Else add p* to R p* augments S, but s does not
Reprocessing nodes • Needed for mesh consistency • Suppose s is added • Enqueue each node ' ≠ s.t. d(s, ') ≤ 2λ
Maintaining light structures • For each node keep: • S = S ∩ • Up ϵ S Fp • Output: union of surface stars Up ϵ S Fp
Termination If insertions are finite, so are enqueues and splits Augmenting R by an existing point does not grow S Consider inserting a new point s Nearest point ≠ p → at least λ/8 from S Insertion due to triangle size → at least λ from S Else → at least εM from S by Proposition 1
Termination Proposition 1 [Cheng-Dey-Ramos-Ray 2007]: εM>0 s.t. if intersections of all edges of Vp with M lie within εM of p then Fp forms a topological disk
Guarantees The underlying space of the output mesh is a 2-manifold without boundary Each point in the output is within distance λ of M λ*>0 s.t. if λ<λ* the output is isotopic to M with Hausdorff distance of O(λ2)
Manifoldness • We require surface stars to fit together globally • Consistency condition: In the output complex UpFp, a triangle abc is in Fa if and only if it is also in Fb and Fc
Manifoldness Theorem: At termination UFp Del S|M Consider the last time is processed; t in Size condition → t in Del S|M when is done If t Del S|M afterward, there is a point s in Delaunay ball. But, s causes to be reprocessed
Topology For sufficiently small λ Homeomorphism follows from [Amenta-Choi-Dey-Leekha 02] Isotopy and Hausdorff distance follow from [Boissonnat-Oudot 05]
Results • Varying does not change the mesh qualitatively
Results • Optimal is platform-dependent
Conclusions A simple algorithm for Delaunay refinement Avoids memory thrashing Topological and geometric guarantees Guarantee of termination Potentially parallelizable