Constrained Delaunay tetrahedralization (boundary recovery) and mesh.tet.generate (M2) (#29)

* predicates: LNC points, generic insphere and its perturbed form (Diazzi et al. 2023 §4.3)

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

* mesh: constrained Delaunay tetrahedralization (segment recovery with LNC Steiner points, gift-wrapping facet recovery, labelling)

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

* cdt: rounding repair, mesh.tet.generate, corpus CDT column; review cleanups (shared perturbation rule, one facet scan, cached coordinates, worklist segment recovery)

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

* mesh.tet.generate is ready in the catalogue; corpus table with the CDT column

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

---------

Co-authored-by: jyviko <[email protected]>
Co-authored-by: Claude Opus 5.5 <[email protected]>
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## Results
| part | categories | bodies | faces | triangles | tol. mm | build ms | enclosed mm³ | SolidCraft mm³ | rel. diff | exact mm³ | boundary | genus | feature edges | check ms |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| bent-tube | sweepable, thin-wall, genus | 1 | 18 | 4296 | 0.121 | 432 | 4213.1 | 4159.4 | 1.3e-2 | 4159.8 | ok, 2148 vertices | 1 | 268 | 11.4 |
| bolted-assembly | assembly, blocky | 3 | 22 | 284 | 0.117 | 57 | 33004.7 | 32999.0 | 1.7e-4 | 32998.9 | ok, 144 vertices | 0, 1, 1 | 104 | 0.7 |
| cross-cylinders | boolean, sharp | 1 | 10 | 1395 | 0.087 | 7548 | 32197.4 | 32357.8 | -5.0e-3 | 32365.8 | error: Cross: invalid boundary surface: 28 defects; triangles 142 and 184 are oriented inconsistently across edge 0–396 at (-15.488656021315903, 4.577998041166734, 7.853092194999726); triangles 184 and 239 are oriented inconsistently across edge 0–554 at (-18.75000000000002, 5.634596901641276, 7.632255089815496); edge 103–108 at (-0.16007784063084018, 0.03984236936862052, 9.998639270596865) is shared by 3 triangles; … | | | |
| filleted-bracket | fillet, genus, sweepable | 1 | 13 | 540 | 0.088 | 388 | 32162.3 | 32145.0 | 5.4e-4 | 32144.8 | ok, 268 vertices | 2 | 135 | 1.4 |
| i-beam | sweepable, thin-wall | 1 | 14 | 44 | 0.208 | 4 | 61600.0 | 61600.0 | 0.0e0 | 61600.0 | ok, 24 vertices | 0 | 36 | 0.1 |
| loft-transition | organic | 1 | 6 | 292 | 0.075 | 54 | 56390.2 | 56450.6 | -1.1e-3 | – | ok, 148 vertices | 0 | 40 | 0.7 |
| perforated-plate | genus, thin-wall, sweepable | 1 | 54 | 1644 | 0.144 | 270 | 26822.2 | 26764.6 | 2.2e-3 | 26764.2 | ok, 776 vertices | 24 | 828 | 4.9 |
| pinhole-block | small-feature, genus | 1 | 38 | 4044 | 0.073 | 206 | 49919.4 | 49909.6 | 2.0e-4 | 49909.5 | ok, 1992 vertices | 16 | 1548 | 12.9 |
| rounded-box | fillet | 1 | 26 | 2540 | 0.054 | 149 | 23325.7 | 23340.5 | -6.3e-4 | 23340.8 | ok, 1272 vertices | 0 | 216 | 6.7 |
| shallow-groove | near-tangent, boolean | 1 | 8 | 62 | 0.075 | 11 | 47795.2 | 47782.3 | 2.7e-4 | 47781.5 | ok, 33 vertices | 0 | 24 | 0.1 |
| sharp-wedge | sharp, thin-wall, sweepable | 1 | 5 | 8 | 0.083 | 2 | 3200.0 | 3200.0 | 0.0e0 | 3200.0 | ok, 6 vertices | 0 | 9 | 0.0 |
| sphere-on-plate | near-tangent, boolean | 1 | 12 | 2826 | 0.098 | 682 | 69353.3 | 69509.0 | -2.2e-3 | 69509.7 | ok, 1415 vertices | 0 | 124 | 6.1 |
| spline-vase | organic | 1 | 11 | 3890 | 0.106 | 217 | 94891.2 | 94948.5 | -6.0e-4 | – | ok, 1947 vertices | 0 | 243 | 8.9 |
| stepped-block | blocky, sharp | 1 | 14 | 96 | 0.078 | 35 | 47000.0 | 47000.0 | 0.0e0 | 47000.0 | ok, 48 vertices | 1 | 60 | 0.4 |
| thin-ribs | thin-wall, blocky | 1 | 26 | 92 | 0.119 | 69 | 32000.0 | 32000.0 | -4.5e-16 | 32000.0 | ok, 48 vertices | 0 | 72 | 0.5 |
| thin-wall-enclosure | thin-wall, blocky | 1 | 11 | 36 | 0.108 | 9 | 15564.0 | 15564.0 | 0.0e0 | 15564.0 | ok, 20 vertices | 0 | 28 | 0.1 |
| analytic-sphere | analytic | 1 | 6 | 2784 | 0.069 | 245 | 33353.4 | 33507.9 | -4.6e-3 | 33510.3 | ok, 1394 vertices | 0 | 96 | 6.1 |
| analytic-torus | analytic, genus | 1 | 6 | 7230 | 0.109 | 334 | 37644.1 | 37893.7 | -6.6e-3 | 37899.3 | ok, 3615 vertices | 1 | 180 | 16.1 |
| analytic-cylinder | analytic, sweepable | 1 | 4 | 1004 | 0.049 | 25 | 12533.1 | 12564.7 | -2.5e-3 | 12566.4 | ok, 504 vertices | 0 | 106 | 2.7 |
| analytic-pipe | analytic, genus, sweepable | 1 | 6 | 1448 | 0.104 | 44 | 94150.9 | 94238.0 | -9.3e-4 | 94247.8 | ok, 724 vertices | 1 | 220 | 3.9 |
| analytic-plate-hole | analytic, genus, sweepable | 1 | 8 | 112 | 0.224 | 11 | 98449.1 | 98429.5 | 2.0e-4 | 98429.2 | ok, 56 vertices | 1 | 62 | 0.4 |
| part | categories | bodies | faces | triangles | tol. mm | build ms | enclosed mm³ | SolidCraft mm³ | rel. diff | exact mm³ | boundary | genus | feature edges | check ms | CDT tets | Steiner | cavities | tet gate | CDT ms |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| bent-tube | sweepable, thin-wall, genus | 1 | 18 | 4296 | 0.121 | 435 | 4213.1 | 4159.4 | 1.3e-2 | 4159.8 | ok, 2148 vertices | 1 | 268 | 10.9 | 15550 | 2338 | 0 | pass | 550 |
| bolted-assembly | assembly, blocky | 3 | 22 | 284 | 0.117 | 54 | 33004.7 | 32999.0 | 1.7e-4 | 32998.9 | ok, 144 vertices | 0, 1, 1 | 104 | 0.7 | 690 | 181 | 0 | pass | 31 |
| cross-cylinders | boolean, sharp | 1 | 10 | 1395 | 0.087 | 7682 | 32197.4 | 32357.8 | -5.0e-3 | 32365.8 | error: Cross: invalid boundary surface: 28 defects; triangles 142 and 184 are oriented inconsistently across edge 0–396 at (-15.488656021315903, 4.577998041166734, 7.853092194999726); triangles 184 and 239 are oriented inconsistently across edge 0–554 at (-18.75000000000002, 5.634596901641276, 7.632255089815496); edge 103–108 at (-0.16007784063084018, 0.03984236936862052, 9.998639270596865) is shared by 3 triangles; … | | | | error: Cross: invalid boundary surface: 28 defects; triangles 142 and 184 are oriented inconsistently across edge 0–396 at (-15.488656021315903, 4.577998041166734, 7.853092194999726); triangles 184 and 239 are oriented inconsistently across edge 0–554 at (-18.75000000000002, 5.634596901641276, 7.632255089815496); edge 103–108 at (-0.16007784063084018, 0.03984236936862052, 9.998639270596865) is shared by 3 triangles; … | | | | |
| filleted-bracket | fillet, genus, sweepable | 1 | 13 | 540 | 0.088 | 381 | 32162.3 | 32145.0 | 5.4e-4 | 32144.8 | ok, 268 vertices | 2 | 135 | 1.4 | 5582 | 1613 | 0 | pass | 187 |
| i-beam | sweepable, thin-wall | 1 | 14 | 44 | 0.208 | 4 | 61600.0 | 61600.0 | 0.0e0 | 61600.0 | ok, 24 vertices | 0 | 36 | 0.1 | 94 | 24 | 0 | pass | 3 |
| loft-transition | organic | 1 | 6 | 292 | 0.075 | 55 | 56390.2 | 56450.6 | -1.1e-3 | – | ok, 148 vertices | 0 | 40 | 0.7 | 1329 | 256 | 1 | pass | 33 |
| perforated-plate | genus, thin-wall, sweepable | 1 | 54 | 1644 | 0.144 | 265 | 26822.2 | 26764.6 | 2.2e-3 | 26764.2 | ok, 776 vertices | 24 | 828 | 4.6 | 33611 | 9798 | 0 | pass | 1195 |
| pinhole-block | small-feature, genus | 1 | 38 | 4044 | 0.073 | 202 | 49919.4 | 49909.6 | 2.0e-4 | 49909.5 | ok, 1992 vertices | 16 | 1548 | 12.4 | 96411 | 30221 | 0 | pass | 4408 |
| rounded-box | fillet | 1 | 26 | 2540 | 0.054 | 156 | 23325.7 | 23340.5 | -6.3e-4 | 23340.8 | ok, 1272 vertices | 0 | 216 | 6.3 | 11666 | 1913 | 0 | pass | 371 |
| shallow-groove | near-tangent, boolean | 1 | 8 | 62 | 0.075 | 11 | 47795.2 | 47782.3 | 2.7e-4 | 47781.5 | ok, 33 vertices | 0 | 24 | 0.2 | 267 | 87 | 0 | pass | 11 |
| sharp-wedge | sharp, thin-wall, sweepable | 1 | 5 | 8 | 0.083 | 2 | 3200.0 | 3200.0 | 0.0e0 | 3200.0 | ok, 6 vertices | 0 | 9 | 0.0 | 11 | 3 | 0 | pass | 0 |
| sphere-on-plate | near-tangent, boolean | 1 | 12 | 2826 | 0.098 | 703 | 69353.3 | 69509.0 | -2.2e-3 | 69509.7 | ok, 1415 vertices | 0 | 124 | 5.7 | 4898 | 309 | 9 | pass | 214 |
| spline-vase | organic | 1 | 11 | 3890 | 0.106 | 230 | 94891.2 | 94948.5 | -6.0e-4 | – | ok, 1947 vertices | 0 | 243 | 8.5 | 12461 | 1512 | 0 | pass | 419 |
| stepped-block | blocky, sharp | 1 | 14 | 96 | 0.078 | 30 | 47000.0 | 47000.0 | 0.0e0 | 47000.0 | ok, 48 vertices | 1 | 60 | 0.4 | 223 | 41 | 0 | pass | 6 |
| thin-ribs | thin-wall, blocky | 1 | 26 | 92 | 0.119 | 62 | 32000.0 | 32000.0 | -4.5e-16 | 32000.0 | ok, 48 vertices | 0 | 72 | 0.5 | 171 | 33 | 0 | pass | 6 |
| thin-wall-enclosure | thin-wall, blocky | 1 | 11 | 36 | 0.108 | 8 | 15564.0 | 15564.0 | 0.0e0 | 15564.0 | ok, 20 vertices | 0 | 28 | 0.1 | 191 | 47 | 2 | pass | 5 |
| analytic-sphere | analytic | 1 | 6 | 2784 | 0.069 | 263 | 33353.4 | 33507.9 | -4.6e-3 | 33510.3 | ok, 1394 vertices | 0 | 96 | 5.8 | 4211 | 58 | 0 | pass | 258 |
| analytic-torus | analytic, genus | 1 | 6 | 7230 | 0.109 | 345 | 37644.1 | 37893.7 | -6.6e-3 | 37899.3 | ok, 3615 vertices | 1 | 180 | 15.4 | 19790 | 466 | 0 | pass | 717 |
| analytic-cylinder | analytic, sweepable | 1 | 4 | 1004 | 0.049 | 25 | 12533.1 | 12564.7 | -2.5e-3 | 12566.4 | ok, 504 vertices | 0 | 106 | 2.7 | 7437 | 1568 | 0 | pass | 259 |
| analytic-pipe | analytic, genus, sweepable | 1 | 6 | 1448 | 0.104 | 43 | 94150.9 | 94238.0 | -9.3e-4 | 94247.8 | ok, 724 vertices | 1 | 220 | 3.7 | 6238 | 1340 | 0 | pass | 264 |
| analytic-plate-hole | analytic, genus, sweepable | 1 | 8 | 112 | 0.224 | 11 | 98449.1 | 98429.5 | 2.0e-4 | 98429.2 | ok, 56 vertices | 1 | 62 | 0.4 | 1868 | 543 | 0 | pass | 53 |
## Categories
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@@ -238,6 +238,21 @@ Delaunay methods with Voronoi/ODT improvement, then (2) all-hex and hex-dominant
- **Complexity.** High: about 8–12k lines of Rust including the predicate generator. It is the single most valuable
investment in the tet pipeline.
- **Code.** `MarcoAttene/CDT` is **GPL, or LGPL by build option** (README): FORBIDDEN.
- **Implemented** in `modelcraft-mesh::cdt` from the paper only, with these choices:
- Steiner points are LNC points (§4.3) on the original segment, `a + t (b − a)` with `t` a double; the in-sphere test
on them is exact (interval filter, then exact dyadic integers) and perturbed with the same lexicographic lift as
the Delaunay step, so Bowyer–Watson insertion of Steiner points stays consistent with it.
- Facet recovery uses the modified gift-wrapping (§4.4) for every cavity, not only after Si's cavity expansion
fails: it is the always-correct path, and Si's expansion is a speed-up. Condition (ii) is an exact
proper-intersection test of closed simplices (separating plane through three of the vertices, then recursion
into the contact plane), which handles the coplanar configurations of CAD tessellations; recovered facets inside
a cavity stay constraints.
- Reference points (§3.3) are searched among the tetrahedra whose boxes meet the missing subsegment's box (they
contain the tetrahedra the subsegment crosses); on the corpus this picks the same point as searching the whole
diametral ball.
- Rounding (§5.1): a Steiner point whose rounding leaves an incident tetrahedron non-positive tries the doubles
within two ulps per coordinate, nearest first; the flip-based improvement of §5.1 is not implemented. All 20
valid corpus parts pass the validity gate after rounding.
**A2.4 Diazzi and Attene 2021, convex polyhedral meshing.** **Verdict: reference.**
- **Citation.** L. Diazzi, M. Attene. *Convex polyhedral meshing for robust solid modeling.* ACM TOG 40(6):259, 2021.