Mesh defects and repair

Copal checks every model you open for defects in its mesh, the triangles that make up its surface. Some defects change what gets printed; others only make the mesh untidy and leave the printed layers as they are. This page lists each defect, whether it matters for a print, and which repair resolves it.

Defect	Changes the print	Fixed by Repair	Fixed by Repair fully
Holes Gaps in the surface, so it does not close around a solid.	Yes: layers around a gap can come out missing or wrongly filled.	Yes	Yes
Open edges Edges with a triangle on one side only. They border holes.	Yes: they leave the solid open.	Yes	Yes
Inconsistent edges Neighboring triangles facing opposite ways.	Yes: the slicer can mistake inside for outside.	Yes	Yes
Inside-out shells A closed part whose surface faces inward.	Yes: the slicer reads its inside as outside.	Yes	Yes
Degenerate triangles Triangles so thin they have no direction.	No: a triangle without area adds nothing to any layer. Repair removes them all the same, as its other steps need them gone.	Yes	Yes
Loose fragments Tiny separate pieces enclosing almost no volume.	Yes: they print as specks that float off into the vat.	Yes	Yes
Self-intersections The surface passes through itself, as where a support is pushed into a model.	No: the slice fills everything the surface encloses.	No	Yes*
Non-manifold edges Surfaces that touch along an edge, as where two parts meet.	No: surfaces that touch slice as one solid.	No	Yes

Repair and Repair fully

Repair resolves every defect that changes the print, and is quick even on large models. It also removes degenerate triangles: filling holes leaves some, and its other steps need them gone. After it, a model prints as its shape intends.

Repair fully also resolves self-intersections and non-manifold edges, for a clean mesh to export or to edit in another program. It takes longer, and it changes nothing in the printed layers.

What Repair fully leaves

Where two thin parts of a model touch along an edge and their faces lie almost exactly in one plane, a few self-intersections can remain. On a very densely supported model this is a handful of places, each a few hundredths of a millimeter across, and none changes a printed layer.

Rarely, a part whose surfaces meet too exactly to be cut apart is left as it was, and the repair report lists it. Slicing fills the space it encloses, so the print is usually unaffected.