estimate_alpha — 3D `reconstruct` op

• Data kinds: points → measurement

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

Usage

Return a recommended alpha from the point set's scale (based on the median nearest-neighbour distance).

Computes the median m of each point's nearest-neighbour distance and returns alpha = 1/(2m) so that the radius threshold 1/alpha ≈ 2m (allowing up to about 2 times the neighbour spacing). This keeps well-behaved tetrahedra near the surface while cutting off largely stretched tetrahedra (= concavities, outside). Duplicate points give a nearest-neighbour distance of 0, so only positive distances are used.

Parameters

points : array_like (N,3)

Returns

alpha : float

Positive finite value.

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)

• alpha_shape_topology — py -3.11 examples_3d/alpha_shape_topology.py

• sfm_recon — py -3.11 examples_3d/sfm_recon.py

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

vol_gaussian_psf · fuse_to_voxel · fresnel_reflectance · snell_angle

Same category (`reconstruct`)

poisson_lite · alpha_shape_mesh · alpha_shape_boundary

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

estimate_alpha — 3D reconstruct op