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RFC 595Title: Modify DE fields of B-REP entities Submitted by: Edward Clapp Description of ProblemDuring gray page testing, it was identified that IGES does not permit assigning many DE attributes (e.g., color, line font) to topological entities; instead, such attributes are applied to the constituent geometric entities. This conflicts with many CAD systems that consider the topological entities "primary" and apply the attributes to them. While mapping between the two approaches is possible, it can be difficult. A similar situation exists for transformation matrices.Proposed Solution1) Add to Manifold Solid B-REP Object Entity (Type 186) and Edge List Entity (Type 504): DE fields 4, 6, 12 and 13.2) Add to Loop Entity (Type 508): DE fields 4, 12 and 13. 3) Add to Shell Entity (Type 514, Form 2 ONLY): DE fields 4, 7, 12 and 13. Analysis: The Type 186, 508, 504, and 514 entities are "collector" entities, so it is preferable to assign display attributes at their level rather than to the many geometric entities they reference. Similarly, the Type 514, Form 2 should be permitted to reference a Transformation Matrix Entity (Type 124) rather than requiring the matrix to be referenced by all the geometric entities referenced by the Type 514. No changes are proposed to the Face Entity (Type 510) since it references only one surface; attributes can be applied to the surface. Posted for comment 11/21/2006 |