Non-Planar Faces#

Description#

Non-planar faces visualization

A non-planar face is a polygon whose vertices do not all lie in the same plane. Non-planar boundary faces can cause tetrahedral meshing to fail or can produce poor-quality boundary triangulation, increasing the risk of sliver, low-volume, or badly angled tetrahedra. Such faces should be planarized or explicitly triangulated before tetrahedral meshing.

Detection#

Detection Method: Perpendicular distance from best-fit plane

Tolerances:

  • Non-Planar Threshold: 1e-4 m (0.1 mm)

Detection process:

  1. Fit a best-fit plane to all vertices of the face (least-squares)

  2. Calculate maximum perpendicular distance of any vertex from the plane

  3. Calculate RMS (root mean square) distance

Note

Tolerances are distance-based (absolute). Large models have the same absolute tolerance, which may be more permissive relative to their size. Unlike zero area faces (which are inherently invalid), moderate non-planarity is often acceptable.

Auto-Repair#

Status: ❌ No automatic repair

Action: Detection and reporting only

Non-planar faces are detected and reported in the issue list but not automatically fixed. This allows users to:

  • Inspect which regions have planarity issues

  • Decide whether to accept the geometry as-is

  • Manually repair in CAD if needed

Why no auto-repair? There is no single “correct” repair for a non-planar face:

  • Project all vertices onto the plane (changes vertex positions)

  • Triangulate into smaller planar faces (increases face count)

  • Re-mesh the region (complex topology changes)

Manual Fix / Avoidance#

In 3D Modelling Tools (Before Export):

  1. Check mesh quality: - Use CAD mesh checking tools - Look for high-aspect-ratio faces or skewed elements - Visualize face normals to spot inconsistencies