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Principal authors: U. Kroszynski, B. Palstr9Sm 1.1 The evolution of concepts and specifications for CAD data exchange The CAD/CAM community has witnessed, during the last decade, the appearance of several specifications as well as proposals for standards which either attempt to cover wider areas or to be more reliable and stable than the others. With the rapid evolution of both hardware and software, the capabilities offered by CAD systems and CAD based application systems are far more advanced than they were only ten years ago, even when they are now based on micro-computers or personal comput ers. The situation with standards, however, is not and cannot be so. In order to be reliable and accepted by a wide community of both vendors and users, a standard has to be sta ble. This implies a life span of at least a decade. This also implies that the standard has to be general and flexible enough to accommodate present as well as expected future developments. 1.1.1 IGES The initial development of concepts for CAD data exchange is strongly influenced by the US Integrated Computer Aided Manufacturing (ICAM) programme, that dealt with the development of methods for data exchange. In September 1979, a subgroup was estab lished with participation of the National Bureau of Standards, the General Electric Com pany, and the Boeing Company. The result of this effort was the Initial Graphics Exchange Specification (IGES) that was published as a NBS report [61] in 1980.
Contenu
Project Overview.- The Transfer of Solid Models.- 1. Introduction.- 1.1 The evolution of concepts and specifications for CAD data exchange.- 1.1.1 IGES.- 1.1.2 Other standards: VDAFS and SET.- 1.1.3 The need for a new standard.- 1.2 Solid modelling techniques.- 2. The CAD*I approach to solid model transfer.- 2.1 General principles.- 2.2 The specification tools.- 2.2.1 Features of the CAD*I specification language HDSL.- 2.2.2 The specification language for the physical file format.- 2.3 Specification of the CAD*I reference model.- 2.3.1 Content.- 2.3.1.1 Attribute types for general use.- 2.3.1.2 General data base structure.- 2.3.1.3 Referencing mechanisms.- 2.3.1.4 Geometric model entities.- 2.3.1.5 Solid models.- 2.3.1.6 General grouping mechanism.- 2.3.1.7 Test data elements.- 2.3.1.8 Miscellaneous.- 2.3.1.9 Parametric modelling.- 2.3.2 Static models and parametric models.- 2.4 Implementation levels.- 2.4.1 The geometric modelling levels.- 2.4.2 The assembly structure.- 2.4.3 Parametric models and macros.- 2.4.4 References.- 2.5 The specification of semantic meaning.- 2.5.1 Generic semantics of the CAD.' data structures.- 2.5.1.1 Creation of data structure elements.- 2.5.1.2 Deletion of data structure elements.- 2.5.1.3 Modification of attributes.- 2.5.1.4 Navigation in the data structure.- 2.5.2 The semantics of post-processors.- 2.5.3 The static semantics of geometric entities.- 2.5.3.1 Curves and surfaces.- 2.5.3.2 Solids.- 2.5.4 Linear transformation of geometric models.- 2.6 Aspects of the physical file format.- 2.6.1 The transport aspect.- 2.6.2 The presentation aspect.- 2.7 Processor implementation.- 2.8 Access to CAD system data bases.- 3. General implementation problems.- 3.1 Access to the CAD system data base.- 3.1.1 Programming interface.- 3.1.2 Access via files.- 3.2 Mapping problems.- 3.3 Inference of the original meaning: Euclid primitives.- 3.4 Missing CAD*I entity example: Pyramid in Bravo3.- 3.5 Implicit model conversion example: CSG input to a B-rep system.- 3.6 Deviations from the reference model: The Bravo3 one-sided Boolean tree.- 3.7 The overlap problem in CSG modelling: a Bravo3 example.- 3.8 Problems related to Boolean operations in Proren2 and Technovision.- 3.9 The effect of truncation errors: receiving boxes in Bravo3.- Specific Implementations.- 4. The CAD*I processors for Schlumberger's Bravo3.- 4.1 System description.- 4.2 Internal representation of CAD models.- 4.3 Existing interfaces.- 4.4 Embedding the processors into the Bravo3 environment.- 4.5 The pre-processor.- 4.5.1 Instances.- 4.5.2 Names.- 4.5.3 Features.- 4.5.4 The mapping from Bravo design input to CAD*I format.- 4.6 Examples of pre-processor conversions.- 4.6.1 Parallelepiped.- 4.6.2 Polyhedron.- 4.6.3 Right Angle Wedge.- 4.6.4 Sphere.- 4.6.5 Right Circular Cylinder.- 4.6.6 Truncated Right Cone.- 4.6.7 Solid Torus.- 4.6.8 Arbitrary Slab.- 4.6.9 Surface of revolution.- 4.7 The post-processor.- 4.8 Examples of post-processor conversions and approximations.- 4.8.1 Examples of the command input file.- 4.8.2 Some details to post-processor transactions.- 4.8.3 Special features.- 4.9 The formal Bravo3 solid model transfer schema.- 4.9.1 Pre-processor schema.- 4.9.1.1 General data base structure.- 4.9.1.2 Points and curves.- 4.9.1.3 Constructive solid geometry.- 4.9.1.4 General grouping mechanism.- 4.9.1.5 Placement and instancing.- 4.9.1.6 Miscellaneous.- 4.9.2 Post-processor.- 4.9.2.1 General data base structure.- 4.9.2.2 Points and curves.- 4.9.2.3 Constructive solid geometry.- 4.9.2.4 General grouping mechanism.- 4.9.2.5 Placement and instancing.- 4.10 Test results.- 5. The CAD*I processors for IBM's Catia.- 5.1 System description.- 5.2 Existing interfaces.- 5.3 Internal representation of CAD models.- 5.4 Embedding the processors in the Catia environment.- 5.4.1 Hardware and operating system.- 5.4.2 Programming Language and Compiler.- 5.4.3 CATGEO routines to access the Catia database.- 5.4.4 Standardisation of routine names.- 5.4.5 Internal programme documentation.- 5.5 The pre-processor.- 5.5.1 Implementation levels.- 5.5.2 The formal Catia solid model transfer schema.- 5.5.3 Programme description.- 5.6 The post-processor.- 5.6.1 Implementation levels.- 5.6.2 The formal Catia solid model transfer schema.- 5.6.3 Programme description.- 5.7 Test results.- 6. The CAD*I processors for Matra Datavision's Euclid.- 6.1 System description.- 6.2 Existing interfaces.- 6.3 Internal representation of CAD models.- 6.4 Embedding the processors into the Euclid environment.- 6.4.1 Pre-processor.- 6.4.2 Post-processor.- 6.5 The mapping from Euclid data structure to CAD*I data structure.- 6.5.1 Processing of Euclid solid primitives.- 6.5.1.1 Processing of the Euclid solid of revolution.- 6.5.1.2 Processing of special cases of Euclid polyhedron entities (BOX).- 6.5.1.3 Processing of general Euclid polyhedron entities.- 6.5.2 The processing of Euclid hybrid solids.- 6.5.3 The processing of the Euclid "figure" entities.- 6.6 The mapping from CAD*I data structure to Euclid data structure.- 6.6.1 Processing of information related to the neutral file.- 6.6.2 Processing of information related to the world.- 6.6.3 Processing of elementary geometric information.- 6.6.4 Processing of composite geometric information.- 6.6.4.1 Mapping of sweep entities to Euclid representations.- 6.6.4.2 Mapping of polyhedron entities to the Euclid polyhedron.- 6.6.5 Processing of structural information.- 6.7 Mapping problems in the pre-processor.- 6.7.1 Mapping problems with the Euclid primitives.- 6.7.2 Mapping problems with Boolean expressions in Euclid.- 6.7.3 Mapping problems with polyhedron entities in Euclid.- 6.8 Mapping problems in the post-processor.- 6.9 Possible enhancements of the processors.- 6.10 Test results.- 7. The CAD*I processors for DTH's GDS.- 7.1 System description.- 7.2 User interaction and internal representation.- 7.3 Existing interfaces.- 7.4 The pre-processors.- 7.4.1 The data base traversal.- 7.4.2 Limitations.- 7.5 An example of pre-processor conversion.- 7.6 The post-processors.- 7.6.1 The data structure.- 7.7 An example of post-processor conversion.- 8. The CAD*I processors for SDRC's Geomod.- 8.1 System description.- 8.2 Existing interfaces.- 8.2.1 IGES.- 8.2.2 Universal file.- 8.2.3 Programme files (log file).- 8.2.4 PEARL data base interface (PDI).- 8.2.5 Internal representation of CAD models.- 8.2.6 Object Representation.- 8.2.7 Polygonal model.- 8.2.8 Context-free geometry.- 8.2.9 Grouping…