CAD Import Difficulties

Learn about possible difficulties you may encounter during CAD import.

If a line does not import correctly and has gaps, the gaps are filled with straight lines. If necessary, pieces of composite curves are reversed to make the entire line continuous. Lines shorter than the object space tolerance are rejected.

A line cannot intersect itself. This condition is not detected, and results may be incorrect if this kind of line is imported. A closed loop can have coincident starting and ending points.

Untrimmed surfaces are corrected if they do not import correctly. Internal gaps (C0-discontinuity) are removed by blending each edge of the gap together. Breaks at C1-discontinuities are controlled internally and may accept lower-level continuities depending on the reader's internal tolerance. While surfaces with one or two dimensions smaller than the object space tolerance are not prohibited, it is likely that they may be rejected.

Each point in the interior of the surface’s parameter space should map to a distinct point in object space. This condition is not detected and incorrect results may occur if such a surface is imported. A surface may be closed in one or both directions.

Trimmed surfaces are a combination of untrimmed surfaces and one or more lines. The above restrictions apply to trimmed surfaces. If a surface cannot be trimmed, as much geometry information as possible is supplied. In most cases, both the underlying surface and its lines are created. It is then possible to use the Surface Edit panel to trim the surface manually.

It is also useful to refer to the .msg files generated by each CAD reader to find warnings/errors that may help in resolving import difficulties.