Tolerant Modeling
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Due to enhanced ACIS functionality when importing problem data (with gaps or other problems) some inaccuracies can be accepted after healing using an ACIS tolerant edge capability.  For example, you can import a model with gaps and heal the model.  If the model doesn’t heal 100% you can place a tolerant edge on the problem edges or rebuild problem faces using the surface create capabilities to sew them into a closed, manifold solid.  By utilizing the tolerant modeling capabilities the gaps and data inaccuracies are allowed to successfully complete the desired operation. 

n        This tolerant edge capability will not accommodate all types of geometry errors and modeling operations.

n        Since tolerant modeling is applied to a body that fails to heal completely and tolerance values are attached to edges and vertices, flawed models from other CAD systems can be modified.  For example, you might only import a set of surfaces that should be a solid; or, two edges might be stitched to one tolerance and another two edges to a different tolerance.  Tolerant modeling technology will allow you to work with these flawed models.  

n        Be aware that when a tolerant modeled body is exported to another format (IGES, STEP, STL), it will continue to have gaps.

n        Tolerant modeling attempts to solve two problems.  The first problem is how faces that do not intersect are represented.  The second problem is how edges that do not intersect are represented.  So even when the edges do not exactly intersect, these will not be regarded as defective models, they will be considered a valid model as a result of tolerant modeling.

n        Tolerant modeling deviates from the assumption that geometry agrees with the topology.  Specifically, the geometry matches the topology with some geometric error.  Tolerant modeling means that the geometric error in the topology has to be taken into consideration when doing modeling operations and calculations.  The approach of tolerant modeling is to tolerate imperfections and work around them: let the software heal as much as possible and then attach tolerance information to uncorrectable areas.