Conformity check

check_conformity(mesh) reports whether a mesh is conforming — whether every two cells meet in a whole shared face, edge or corner with the same point ids on both sides — and, where it is not, which points hang and which facets only partly overlap. It answers the question find_interface leaves to the caller ("conforming" or "proximity"?), and gives refine and undo_green, whose conformity was only discussed in comments, a checker.

import meshioplusplus as mp

mesh = mp.read("assembly.vtu")

checked, report = mp.check_conformity(mesh, return_report=True)
report["conforming"]          # False
report["num_hanging_nodes"]   # 12
report["interface_mode"]      # "proximity": pass that to find_interface
mp.write("flags.vtu", checked)  # conformity:hanging marks the hanging nodes

What it reports

The mesh's volume cells are examined when it has any, else its 2-D cells; lines and vertices are ignored, and a mesh of nothing else reports dimension 0 with a warning. Only the unmatched facets — a face one volume cell uses, an edge one 2-D cell uses — can hold a defect: a node hanging on a face is always a corner of an unmatched facet on the finer side, and a face its neighbour matches cannot hold one.

Defect	Rule	Counted as
hanging node (3-D)	a point some cell uses lies on a face of a volume cell — inside it or on one of its edges — that does not use it	num_hanging_nodes, flag 1
T-junction (2-D)	a point some cell uses lies on the interior of an edge of a 2-D cell that does not use it	num_t_junctions, flag 2
partial overlap	two unmatched facets lie in one plane (on one line) and overlap over a positive area (length) without being one facet	num_partial_overlaps, per pair
unwelded facets	two unmatched facets have coincident corners but different point ids	num_unwelded_facets, per pair

A cell's own nodes are never flagged against it, so the mid-edge nodes of quadratic cells do not hang. Two points closer than the tolerance are one location: a point on a facet's corner is an unwelded duplicate, not a hanging node. A hanging node also shows as partial overlaps — the coarse face against each fine face on it — so a mesh with hanging nodes is never "conforming" in either count.

The report also has num_boundary_facets (the unmatched facets examined, the domain's boundary included), num_non_manifold_facets (facets three or more cells use), dimension, conforming (none of the four defects), warnings (blocks with no known face topology, polyhedra that are not closed) and interface_mode:

interface_mode	When	What to do
"conforming"	nothing reported	find_interface(mode="conforming") matches the facets by their point ids
"weld"	only unwelded facets	merge the coincident points (clean or merge(weld=True)), then "conforming"
"proximity"	hanging nodes, T-junctions or partly overlapping facets	find_interface(mode="proximity"), with the coarse side as master

Output

The input, bit-identical — points, connectivity, block order, every data array and region — with one int64 point-data array, conformity:hanging: 0, 1 for a hanging node, 2 for a T-junction. attach_flags=False leaves it off.

Tolerance

tolerance (default 1e-9) is a fraction of the bounding-box diagonal of the examined facets' corners: a distance at or below it counts as zero, in every test — a point on a facet, a point on a corner, a facet in another's plane. A midpoint computed as (a + b) / 2 is within a few units in the last place of its edge, far inside the default; points an algorithm moved off a facet by more than the tolerance are not on it.

Probes

The tests hold the check to meshes whose defects are known by construction: refine(closure="balanced") flags exactly the points refine:hanging marks, the "redgreen" and "propagate" closures report nothing, an octree with transition="polyhedra" or "templates" reports no hanging node and with "hanging" flags exactly octree:hanging, and undo_green's restored green parents leave T-junctions beside the red children they meet. The notebook example/python/43_conformity_and_planes.ipynb runs the same probes on an octree of the Stanford bunny and on two parts meshed apart.

Core only

The check runs in the compiled core and has no numpy twin: its geometric tests would be a second implementation of the same tolerances to keep in step, and the wheels always carry the core. Without the core, the Python entry point raises NotImplementedError naming it.

CLI

meshioplusplus check-conformity IN [OUT] [--tolerance T] [--json]

Exit status 0 when the mesh is conforming, 1 when it is not and 2 when it could not be checked, as for check. OUT writes the mesh with conformity:hanging.

Pipeline

{ "Op": "CheckConformity", "Tolerance": 1e-9, "Require": true, "AttachFlags": false }

A gate by default: a mesh that is not conforming stops the pipeline with the counts as the error. "Require": false only reports (NumHangingNodes, NumTJunctions, NumPartialOverlaps, NumUnweldedFacets), and "AttachFlags": true writes conformity:hanging onto the mesh that flows on. See pipelines.

Bindings

C: mio_check_conformity(mesh, &opts, &report) with mio_conformity_opts (48 bytes, initialized by mio_conformity_opts_init) and mio_conformity_report (104 bytes, interface_mode a mio_conformity_mode), both with reserved tails, and mio_check_conformity_warnings. Fortran m%check_conformity([tolerance, attach_flags, report, warnings]), Julia check_conformity(m; tolerance, attach_flags), R mio_check_conformity(mesh, tolerance, attach_flags), WASM checkConformity(mesh, {tolerance, attachFlags}) and the MCP tool check_conformity (with an optional output_path).