The Shape Healing module is a standard kit available for users of the certified version of Open CASCADE on all platforms supported by Open CASCADE (Linux, Sun Solaris, Windows).
It provides a comprehensive functionality to heal various defects and inconsistencies in shapes and optimize shapes for use in Open CASCADE.
One of the main uses of Shape Healing is Advanced Data Exchange module. It provides advanced functionality for translation Open CASCADE shapes to and from IGES and STEP formats. It is based on Open CASCADE IGES and STEP translators, but provides much better reliability, performance and quality.
The paragraphs below explain the differences between Advanced Data Exchange and Open CASCADE translators, and give detailed information on functionality provided by Shape Healing toolkit.
Open CASCADE IGES and STEP translators
IGES and STEP translators in Open CASCADE can read and write IGES files conforming to IGES standard in version 5.3 and to STEP AP203 and AP214 (both CD and DIS versions) standards. The translators themselves as they are published in Open CASCADE provide all the necessary classes and tools to map IGES and STEP entities into Open CASCADE shapes:
- classes representing IGES and STEP entities and whole models with relationships between entities
- conversion from IGES and STEP entities to Open CASCADE shapes and vice-versa
- convenient API to perform the translation
These tools provide good results on perfect IGES and STEP files that fully conform to IGES (or STEP) rules and satisfy Open CASCADE requirements for validity of shapes.
However, many of IGES and STEP files encountered in real practice have some inconsistencies that lead to invalidity of shape resulting from translation. The Advanced Data Exchange module is intended to deal with such cases.
Advanced Data Exchange
The Advanced Data Exchange module features Shape Healing toolkit to heal various problems which may be encountered in shapes, so as to make shape valid in Open CASCADE. The Shape Healing is smoothly connected to IGES and STEP translators: the same API as for Open CASCADE IGES and STEP translators is used, just names of API packages change.
Here are a few examples of typical problems that can be encountered in real IGES and STEP files, with illustrations of how Shape Healing deals with them:
Face with missing seam edge
The problem: Face on a periodical surface is limited by wires which make a full trip around the surface. These wires are closed in 3d but not closed in parametric space of the surface. This is not valid in Open CASCADE.
The solution: Advanced Shape Healing fixes this face by inserting seam edge which combines two open wires and thus closes the parametric space. Note that internal wires are processed correctly.
Wrong orientation of wires
The problem: Wires on face have incorrect orientation, so that interior and outer parts of the face are mixed.
The solution: Advanced Shape Healing recovers correct orientation of wires.
The problem: Face is invalid because its boundary wire has self-intersection (on two adjacent edges)
The solution: Advanced Shape Healing cuts intersecting edges at intersection points thus making boundary valid.
The problem: There is a gap between two edges in the wire, so that wire is not closed
The solution: Advanced Shape Healing closes a gap by inserting lacking edge.