Boundary Representation Data Exchange and Healing
Compared to the exchange of simple geometry, the data exchange of boundary representation models requires some level of approximation and repair. Translation is difficult because of the additional connectivity information present in the model and the different system level interpretations of model validity.
For example, in a boundary representation model, vertices must lie on certain edges. In terms of an engineering model system, this means that the point representing a vertex must lie within a distance of 0.001 units from the curve representing the edge. However, when this file is exported and then re-imported into a target system, the target system may assume that a vertex lies on an edge only if the point representing the vertex lies within a distance of 0.0000001 units from the curve representing the edge.
Because of different system tolerances, the model considered valid in the exporting system may not be considered valid in the importing system. Also, geometry considered valid in the exporting system may not be considered valid in the importing system. Therefore, exchange of boundary representation models is usually not a completely successful process. Healing of the imported model is necessary so that it can be used later in the importing system.