decimate_qem — 3D `mesh_process` op

• Data kinds: mesh → mesh

• Call: import fullseye as fs; fs.ledger.decimate_qem(V, F, target_faces, protect=None) (to call the implementation directly, import meshrepair; meshrepair.decimate_qem(V, F, target_faces, protect=None); from the registry, ops3d.get("decimate_qem"))

Usage

Quadric-error-metric edge-collapse decimation toward *target_faces*.

*protect* (optional, (nv,) bool): vertices that must survive untouched —

no edge incident to a protected vertex is collapsed, so the faces around a

crater rim, a boulder or any region you flagged keep their exact geometry

(`meshres.mesh_decimate_preserving` derives the mask from the detail map

and reports what the rest of the reduction lost).

Garland & Heckbert 1997: each vertex carries the sum of the squared-distance

quadrics of its incident face planes; the cheapest edge is collapsed to the

position minimising that quadric (a midpoint/endpoint fallback when the 3x3

system is singular, e.g. on a flat face), quadrics are accumulated onto the

surviving vertex, and incident edge costs are re-queued. Collapses that would

flip a face normal or land on a non-manifold edge are skipped, so the result

stays a sane surface.

Honest scope: this is a practical QEM, not production-grade. It has no

boundary-preservation term, no attribute (colour/UV) quadrics and no

aggressive validity recovery, so on awkward meshes a few non-ideal collapses

can survive and the collapse may stop a little short of *target_faces* when

every remaining candidate is blocked by the flip/manifold guard. Good enough

for a cheap collision proxy; not a replacement for a dedicated remesher.

Background guides (the physics and conventions behind this op)

• blender_interop — Blender との併用 — 形を作って fullseye で測る(軸・単位・正解データの罠)

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)

• mesh_decimate — py -3.11 examples_3d/mesh_decimate.py

• mesh_lod_download — py -3.11 examples_3d/mesh_lod_download.py

• mesh_resolution_demo — py -3.11 examples_3d/mesh_resolution_demo.py

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

mesh_to_voxel · mesh_to_points · to_points · fuse_to_voxel · ambient_occlusion · cast_shadow · supersample_mesh · render_beauty

Same category (`mesh_process`)

laplacian_smooth · taubin_smooth · face_normals · vertex_normals · mesh_area · vertex_curvature · face_areas · mesh_volume

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

decimate_qem — 3D mesh_process op