VoxelForge/Standalone/Research/WorldAssemblerM3/Research29/first-pass.md

Research29 — L59 open shaft rim

Mechanism

The L59 dimensions make the ramp’s inner boundary exactly coincide with the core boundary: 6.0 m centerline radius minus 1.5 m passage radius equals the 4.5 m core radius. The ramp has a 1.0 m support depth and a 5.0 m pitch. (Linux59 report records these dimensions; Standalone/Research/WorldAssemblerM3/Linux59/REPORT.md:5.)

The core void is a hard intersection:

radial = hypot(dx, dy) - radius;
bottom = floor - point[2];
featureVoid = max(radial, bottom);

wip/l59-open-shaft:Standalone/Core/src/ShapeWorldInternal.h:7340–47

The ramp void is an annular tube intersected with the floor/ceiling interval. The interval uses a hard max, then the tube and interval use cubic smooth-max:

corridorSdf = max((floorZ-point[2])*scale,
                  (point[2]-(floorZ+height))*scale);
featureVoid = SmoothMaxMetres(tube, openHelixVerticalSdf, width);

ShapeWorldInternal.h:7410–17, 7522–25. Core and ramp voids are then combined by smooth-min, falling back from unionWidth to smoothWidth, before subtraction from constant host rock: ShapeWorldInternal.h:7532–50.

The leading suspect is the coincident, oppositely directed zero surfaces at the core/ramp contact. With zero or insufficient union width, the touching voids form a sharp or pinched seam. Marching Cubes samples that off-grid feature with its ordinary cell topology; the resulting aliasing is consistent with the torn shards. Kobbelt et al. describe severe alias artifacts at sharp features in regular-grid surface extraction and explain that grid refinement alone does not resolve the normal error (paper). The ramp floor/tube intersection is smooth-max blended, but its actual width and the feature-union width are absent from the tracked L59 report.

There is also a likely support-field defect. The open-helix support uses:

vertical = max((floorZ-point[2])*scale,
               (point[2]-(floorZ-supportDepth))*scale);
supportSdf = max(nearestRadial-radius, vertical);
composed = min(composed, latticeFloorSupportMinimum);

ShapeWorldInternal.h:7497–15, 7551–55

With VoxelForge’s negative-solid, positive-air convention, this vertical expression is nonnegative everywhere; it is positive inside the intended below-floor slab. The final min therefore cannot add negative solid there. A negative-inside support slab would reverse both vertical terms. This is a high-confidence sign concern from the equations, but I cannot isolate its visual effect without field samples. The hard support cap can also distort field values after the smooth feature union.

The reported 1 m support is four LOD0 cell steps at 0.25 m, so support thickness alone is unlikely to explain the LOD0 capture. It is only two steps at 0.5 m and falls below one cell at a 2 m step. Relief noise is unlikely to be the cause: the open-shaft path bypasses the legacy cap path, where the noise evaluation lives (ShapeWorldInternal.h:7187–91, 7249–55).

Construction and numbers

Build one continuous core-plus-ramp void, smooth-union its components, then subtract that void from the host once. Encode the ledge floor in the void definition and remove the post-union support cap; preserve the support as negative solid in the composed field. Verify that smoothing keeps the intended 4.5 m core opening.

For the current cubic smooth-max, Research16 estimates a local fillet radius R ≈ W/(2√2) for perpendicular unit-gradient fields (Research16/REPORT.md:29–31). Applied as a sizing guide:

Mesh step h	Minimum bullnose R=2h	Approx. width W=2√2R	Slab thickness T≥2R*
0.25 m	0.50 m	1.41 m	1 m
0.50 m	1.00 m	2.83 m	2 m
2.00 m	4.00 m	11.31 m	8 m

*For a bullnose that rounds both the top and underside. A preferred R=3h increases the required width and thickness by 50%. These are sampling targets, not guarantees; measure the composed field because its gradients and intersection angles vary.

At LOD0, the existing 1 m support only meets the minimum two-sided bullnose thickness, with no margin. A 0.75 m radius is a safer preferred LOD0 target and calls for at least 1.5 m of slab.

Far LODs

The L59 capture command forces --max-level=0 (CaptureNativeLatticeL59.py:78–85), so it provides no evidence for coarser meshes. With the owner defaults (0.25 m Core voxels, full_res_clip_levels=2, coarse_tile_cells=16) and the mesher’s extent/cell calculation (VoxelForgeCore.cpp:2121–22), nominal steps are 0.25 m at LOD0, 0.5 m at LOD1, then 2, 4, 8, 16, 32, 64, 128 m at LOD2–8. The ramp is a resolved cavern edge; the separate fine-resolution override checks type-4 world-assembly shelf features (VoxelForgeCore.cpp:2124–49).

A fixed 1 m ledge cannot survive those far steps. Keep the detailed ledge in near LODs, refining ramp tiles where needed. At far LODs, fade it into a broad, rounded wall bump and then out of the silhouette. Do not keep thickening the walkable slab: at LOD2 the two-sided bullnose sizing already asks for an 8 m slab and an 11.3 m smooth width against a 3 m passage.

Audit and slice plan

The L59 audit uses a 0.25 m corridor margin and excludes the shaft-core room from its room ROI (AuditLatticeSurfaceL59.py:82–91, 159–205, 229–48). That leaves only a one-voxel allowance for shards protruding into the core. Expand the ROI and its bounds to cover at least a 1 m band on both sides of each free edge, plus the full 1 m underside and headroom. Add edge-specific coverage and roughness measurements so the free rim is scored even when its triangles cannot serve as smooth reference terrain.

Run the raw L59 mesh as a negative control with expect=fail; require the edge defect to be detected. Require the corrected candidate and plain-native control to pass. Include all four turns, both free edges, and the support underside.

Proposed slices: sample radial/vertical sections through the core and ledge at quarter-turn intervals and multiple azimuths, at 0.0625 m increments. Record the core, ramp, support, union, and final density values. Then compare current and corrected LOD0 meshes across half-cell grid phases; inspect LOD1 and LOD2 transitions, followed by the far-LOD bump/fade through LOD8. The existing audit phase option shifts its analytical reference; it does not remesh a shifted grid.

Uncertainty

The tracked L59 report does not give the resolved smoothWidth or unionWidth, and the branch has no raw mesh/audit JSON here to localize the shard triangles. The tangent-seam diagnosis is therefore likely, not proven. The support sign reversal is directly visible in the equations and deserves field-level confirmation.

Read-only inspection only; no files were changed and no tests or binaries were run.