alpha_shape_boundary — 3D `reconstruct` op

• Data kinds: points → indices

• Call: import fullseye as fs; fs.ledger.alpha_shape_boundary(points, alpha) (to call the implementation directly, import recon3d; recon3d.alpha_shape_boundary(points, alpha); from the registry, ops3d.get("alpha_shape_boundary"))

Usage

The indices of the boundary points by alpha shapes (point set → boundary points).

Collects the surface triangles (boundary faces) of the Delaunay tetrahedra whose circumsphere radius < 1/alpha, and takes their vertex set as the boundary points. Suited to extracting only the surface-shell points from a solid (surface + interior) point cloud. Making alpha larger makes the allowed radius 1/alpha smaller, giving a tighter boundary (one that picks up fine detail).

Parameters

points : array_like (N,3)

alpha : float

Positive real number. The radius threshold is 1/alpha. estimate_alpha gives a rough guide.

Returns

boundary_point_indices : numpy.ndarray (K,) int64

Indices of the boundary points into points (ascending, no duplicates). Empty array if there is no boundary.

Background guides (the physics and conventions behind this op)

• blender_interop — Using Blender alongside — build the shape, measure it with fullseye (pitfalls: axes, units, ground truth)

References (sample data, literature)

• Sample-data catalog (download URLs / licences) — 2-D uses skimage.data (BSD/public domain) plus synthetic images; 3-D lists download URLs for real data sources (Stanford, PDS, …).

• Operator provenance and references — the sources of the research/methods this op family came from.

Runnable examples (verified samples that actually call this op)

• sfm_recon — py -3.11 examples_3d/sfm_recon.py

Ops the type connects to (they accept `indices` as input)

fuse_to_voxel

Same category (`reconstruct`)

poisson_lite · alpha_shape_mesh · estimate_alpha

*Provenance: recon3d.py — 3D operator registry. This per-op note is generated by tools/opdocs.py md (do not hand-edit).*

alpha_shape_boundary — 3D reconstruct op