delaunayRefine: guard against inserting a circumcenter coincident with an existing vertex#249
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…ng vertex Constrained delaunayRefine (edges fixed via setMarkedEdges) could trace a circumcenter onto an existing vertex -- it ends as a Face point on a triangle corner -- creating a zero-area "needle" triangle that poisons downstream cotan-Laplacian / BFF solves. After insertVertex, if the new vertex has a near-zero incident edge (minInc <= 1e-9 * maxInc) it landed on existing geometry: undo the insertion and return Vertex(). delaunayRefine already treats a Vertex() return as "insertion failed" and continues, leaving the unrefinable constrained corner as a healthy (non-degenerate) triangle. Upstream report: nmwsharp#246
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Fix for #246.
Constrained
delaunayRefine(edges fixed viasetMarkedEdges) can trace acircumcenter onto an existing vertex — it ends as a
Facepoint on a trianglecorner — producing a zero-area "needle" triangle (min angle 0°, ~1e-9 edge)
that then poisons downstream cotan-Laplacian / BFF solves. The same mesh and
metric refine cleanly to the angle bound when no interior edges are marked, so
only the segment-constrained path hits it.
This adds a proximity guard in
IntrinsicTriangulation::insertCircumcenter:after
insertVertex, if the new vertex has a near-zero incident edge(
minInc <= 1e-9 * maxInc) it landed on existing geometry, so undo theinsertion and return
Vertex().delaunayRefinealready treats aVertex()return as "insertion failed" and continues, leaving the unrefinable constrained
corner as a healthy (non-degenerate) triangle.
On the reproducer in #246 (stock build, otherwise unchanged): constrained refine
0° → 4.21°, no degeneracy, deterministic; the unmarked control on the
identical mesh is unchanged at 25.12°.
Full analysis + runnable reproducer: #246.
Fixes #246.