About the Representation of Face Boundaries

Below are listed some facts about the representation of face boundaries.

The corresponding options are found in the IGES section of the Preferences.

There are two types of IGES faces:

  • Trimmed Parametric Surfaces (IGES entity type 144).
  • Bounded Surfaces (IGES entity type 143).

Trimmed and bounded surfaces are transformed into faces.

They are defined by:

  • A support surface, e.g. IGES entity of the following types:
    • 120: Surfaces of Revolution
    • 122: Tabulated Cylinders
    • 128: BSpline Surfaces.
  • One or more boundaries (IGES entity types 142 and 141, resp.) that have two representations:
    • 2D or P-Curves (parametric)
    • 3D (spatial).

For each boundary, the IGES file contains a parameter defining the preferred representation:

  • 3D
  • 2D
  • None
  • Equal preference.

In the three last cases, 3DEXPERIENCE tries to import the 2D representation of the boundary. In case of failure, the 3D representation is imported. If the preferred representation is 3D, but if there is a failure, then the 2D representation will be imported.

3D curves can be used with every type of surfaces and curves whereas 2D curves can be used:

  • When the surface is
    • BSpline (type 128)
    • Non-closed C2 Ruled surface (type 118)
    • Surface of revolution (type 120) or
    • Tabulated cylinder (type 122)
  • and if these curves are P-Lines (type 110, form 0) or P-Nu(r)bs (type 126).

Using 2D or P-Curves instead of 3D Curves as face boundaries allow better performance (it is not necessary to lay down or project 3D Curves on the surfaces) and quality improvements (faces that could be KO because of invalid, unsupported or missing 3D Curves will be processed with P-Curves and correctly transferred).