Geometry and Topology Error Reference (Repair and Construction)

Geometry Errors

Self-intersecting surfaces

A surface that folds onto itself is a self-intersecting surface. Surfaces must be continuous and smooth without changing direction.

Self-intersecting curves

Curve data comprises lines, arcs, or splines. Curves must be smooth without changing direction. Curves cannot reverse, twist, or intersect.

Modeling Uncertainty

The bodies or surfaces have low level errors.

Overlapping Faces

Two or more faces are coplanar or overlay each other.

Intersecting Faces

Two or more faces converge or pass through one another.

Irregular Surfaces

The generated surface that was approximated during translation did not fit within system tolerances of the original surface in the imported file. Or, a point on the surface is not pointing in the same direction as the rest of the surface.

These errors can occur if surfaces are twisted or collapse into a small area.

Irregular Curve

Math data is inconsistent in the curve definition or a vector is zero. This error can occur when the approximating surface does not fit within the system tolerance of the defining surface in the neutral file.

Singularity surface

A point on the surface vector is poorly defined. The surface normal cannot be determined.

Degenerate surface

The points that comprise the surface are in an area that is too small.

Surface discontinuities

The normal direction or curvature of the surface changed abruptly. The error may be caused by disconnected geometry. Surfaces must be smooth and cannot have an abrupt change in direction (G0).

Curve discontinuities

Curve data comprises lines, arcs, or splines. Curves must be smooth without abruptly changing direction (G0) and cannot have an abrupt transition between curves.

Topology Errors

Loop orientation

The outer loop is going in a wrong direction compared to the face normal direction. If the face includes islands (loops enclosed within the outer loop), the normal direction of the islands must point opposite to the outer loop.

Loop direction is defined by the start and endpoint and direction indicator. In addition to the loop and islands having the same direction, a surface has a normal direction that must agree with the loop direction.

If any of the directions are opposite the others, an error is found.

Face orientation

The top side of a face is referred to as the surface normal. Adjacent faces within a solid must all have the same normal direction. For example, all six faces of a box must point in to be a valid solid.

The loop direction is inconsistent with the normal direction of the face or inner loops do not agree with each other.

Loop connectivity (Construction Environment Only)

Geometry such as lines, arcs, and splines are combined into structures. Many edges and geometry can be combined into structures referred to as loops. Loops are used as boundaries on surfaces and trim a potentially infinite size to a face. Sometimes the structure of the loop is incorrect in the neutral IGES or STEP file.

Duplicate vertices

Start and endpoints of an edge are vertices. During translation, attempts are made to merge vertices that fall within the system tolerances. Duplicate vertices can occur when extremely small edges make up a complex object.

Bad face missing data (Construction Environment Only)

The face does not have its underlying geometric definition and is incomplete. Typically, the face cannot be used for modeling.

Bad edge missing data (Construction Environment Only)

The edge does not have its underlying geometric definition and is incomplete. Typically, the edge cannot be used for modeling