Specification of a CAD * I Neutral File for CAD Geometry

ESPRIT Project 322, "CAD Interfaces", has been established to define the most important interfaces in CAD/CAM systems for data exchange, data base, finite element analysis, experimental analysis, and advanced modeling. The definitions of these interfaces are being elaborated in harmony with international standardization efforts in this field. One principal goal of the project is to develop techniques for the exchange of CAD information between CAD systems, and from the CAD domain to CAA (Computer Aided Analysis) and CAM (Computer Aided Manufacturing). This volume presents a proposal for a neutral file format for CAD data: curves, surfaces, and solids. The specification is based on a reference schema for CAD data bases and is defined informally with respect to its semantics and formally with respect to its syntax. This volume is a revised edition of "Specification of a CAD*I Neutral File for Solids" Version 3.2. The revision reflects the enhancements which result from the implementation of communication processors in eight different CAD systems and from the practical exchange of solid models between these systems. Due to the close interaction between the CAD*I project and the coming-up international standard STEP this specification also serves as an introduction to the geometry model that will be included in the future international standard.

to the Specification.- 1.1 Purpose.- 1.2 The relation between this proposal and STEP.- 1.3 Stucture of the document.- Approach.- Basic principles.- 3.1 Use of formal languages.- 3.2 Informal description of the CAD data schema.- 3.2.1 Entities and attributes.- 3.2.2 References.- 3.2.3 Properties.- 3.2.4 Scope.- 3.2.5 World.- 3.2.6 Assemblies and components.- 3.2.7 Geometry.- 3.2.7.1 Curves and surfaces.- 3.2.7.2 Solids Models.- 3.2.7.3 Instancing and placement.- 3.2.8 User-defined name.- 3.2.9 Libraries and external references.- 3.2.10 Parametric Models and macros.- 3.2.11 User records.- 3.2.12 Grouping mechanisms.- 3.3 The physical level.- 3.3.1 Strictly sequential,free format,block structure.- 3.3.2 Metafiles,letters and alphabets.- 3.4 Validation of the CAD model transfer.- 3.4.1 Validation of the opertational behaviour of the model.- 3.4.2 Validation of the geometry.- Reference Manual.- The high level data specification language HDSL.- 4.1 Type declaration.- 4.2 Predefined types.- 4.2.1 The type Integer.- 4.2.2 The type Real.- 4.2.3 The type Logical.- 4.2.4 The type String.- 4.2.5 The type User_Defined_Name.- 4.2.6 The NIL.- 4.2.7 The D2,D3.- 4.2.8 The type Arithmetic_Expression.- 4.3 Composite types.- 4.3.1 Enumeration types.- 4.3.2 Fixed structures types.- 4.3.3 Lists.- 4.3.4 Classes.- 4.4 The types Reference,Ref_Only.- 4.5 Generic types.- 4.5.1 Parametric enumeration types.- 4.5.2 Parametric structure.- 4.5.3 Parametric lists.- 4.5.4 Parametric classes.- 4.5.5 Variant structures.- 4.5.6 Variant classes.- 4.5.7 Generic structures.- 4.5.8 Generic enumerations.- 4.5.9 Generic classes.- 4.5.10 Generic lists.- 4.6 The predefined function Dimension.- 4.7 Rules applying to building a schema with HDSL.- 4.8 Semantics of reference models defined with HDSL.- 4.8.1 Entering entities.- 4.8.2 Interrogating the information content of the environment.- 4.8.3 Identifying entities by textual means.- 4.8.4 Identifying entities by interacvite picking.- 4.8.5 Identifying properties.- 4.8.6 Creating a new entity.- 4.8.7 Creating a new property or relation.- 4.8.8 Deleting an existing entity.- 4.8.9 Deleting an existing property or relation.- 4.8.10 Modifying values of attributes.- 4.8.11 Invoking a modeling function.- 4.8.12 Invoking evaluation functions.- 4.8.13 Linear transformations.- The CAD*I reference model specification.- 5.1 Attribute types for general use.- 5.1.1 Any.- 5.1.2 Dim.- 5.1.3 Type_ID.- 5.1.4 Update.- 5.1.5 List of predefined values.- 5.2 General data base structure.- 5.2.1 World.- 5.2.2 Assembly.- 5.2.3 Component.- 5.2.4 Part_Library.- 5.2.5 Routine_Library.- 5.3 Referencing mechanisms.- 5.3.1 Index_Entry.- 5.3.2 Ref_External.- 5.3.3 Ref_Part_Library.- 5.3.4 Ref_Any.- 5.4 Geometric model entities.- 5.4.1 Geometric_Model.- 5.4.2 Wireframe_Model.- 5.4.3 Surface_Model.- 5.4.4 Solid_Model.- 5.5 Points and Curves.- 5.5.1 Attribute types related to curves.- 5.5.1.1 Curve_Transition_Code.- 5.5.2 Direction.- 5.5.3 Point.- 5.5.4 Curves classes.- 5.5.4.1 Curve.- 5.5.4.2 Elementary_Curve.- 5.5.4.3 Bounded_Curve.- 5.5.4.4 Closed_Curve.- 5.5.5 Elementary curves.- 5.5.5.1 Line.- 5.5.5.2 Line_Segment.- 5.5.5.3 Circle.- 5.5.5.4 Ellipse.- 5.5.5.5 Hyperbola.- 5.5.5.6 Parabola.- 5.5.5.7 Polygon.- 5.5.5.8 B_Spline_Curve.- 5.5.6 Derived curve entities.- 5.5.6.1 Trimmed_Curve.- 5.5.6.2 Composite_Curve.- 5.5.7 Curves with functional dependency.- 5.5.7.1 Offset_Curve.- 5.6 Surfaces.- 5.6.1 Surface classes.- 5.6.1.1 Surfaces.- 5.6.1.2 Rectangular_Surface.- 5.6.1.3 Elementary_Surface.- 5.6.2 Planar_Surface.- 5.6.3 Spherical_Surface.- 5.6.4 Conical_Surface.- 5.6.5 Cylindrical_Surface.- 5.6.7 B_Spline_Surface.- 5.6.8 Surface_of_Revolution.- 5.6.9 Surface_of_Translation.- 5.6.10 Rectangular_Trimmed_Surface.- 5.6.11 Rectangular_Composite_Surface.- 5.6.12 Curve_Bounded_Surface.- 5.6.13 Offset_Surface.- 5.7 Geometry on surfaces.- 5.7.1 Surface_Curve.- 5.7.2 Classes of curves on surfaces.- 5.7.2.1 Curves_On_Surface.- 5.7.3 Point_On_Surface.- 5.7.4 Curves on surfaces.- 5.7.5 Elementary curves on surface.- 5.7.5.1 Elementary_Curve_On_Surface.- 5.7.5.2 Line_Segment_On_Surface.- 5.7.5.3 B_Spline_Curve_On_Surface.- 5.7.6 Intersection_Curve.- 5.7.7 Derived curves on surfaces.- 5.7.7.1 Trimmed_Curve_On_Surface.- 5.7.7.2 Composite_Curve_On_Surface.- 5.8 Boundary representations.- 5.8.1 Standard boundary representation.- 5.8.1.1 B_Rep.- 5.8.1.2 Shell.- 5.8.1.3 Face.- 5.8.1.4 Face_Surface.- 5.8.1.5 Loop.- 5.8.1.6 Edge_Loop.- 5.8.1.7 Edge.- 5.8.1.8 Edge_Curve.- 5.8.1.9 Vertex_Loop.- 5.8.1.10 Vertex.- 5.8.2 The Poly_Hedron:a boundary representation with planar faces.- 5.8.2.1 Poly_Hedron.- 5.8.2.2 Poly_Shell.- 5.8.2.3 Poly_Face.- 5.8.2.4 Poly_Loop.- 5.8.3 An experimental compound boundary representation.- 5.8.3.1 Compound_B_Rep.- 5.8.3.2 Region.- 5.9 Constructive solid geometry.- 5.9.1 Construct.- 5.9.2 Boolean.- 5.9.3 Bool_Operand.- 5.9.4 Bool_Operator.- 5.9.5 Primitive.- 5.9.6 Primitives for consturctive solid geometry.- 5.9.6.1 Planar_Halfspace.- 5.9.6.2 Regular_Prism.- 5.9.6.3 Box.- 5.9.6.4 Solid_Cylinder.- 5.9.6.5 Solid_Sphere.- 5.9.6.6 Truncated_Cone.- 5.9.6.7 Truncated_Pyramid.- 5.9.6.9 Solid_Torus.- 5.9.6.10 Contour_Element.- 5.9.6.11 Linear_Sweep.- 5.9.6.12 Rotational_Sweep.- 5.10 Hybrid_Solid.- 5.11 General grouping mechanism.- 5.11.1 Aspect.- 5.11.2 Geometry_Association.- 5.12 Placement and instancing.- 5.12.1 Geometric.- 5.12.2 Instance.- 5.12.3 Rotation.- 5.12.4 Rot_Axis.- 5.12.5 Rot_Global.- 5.12.6 Rot_Matrix.- 5.12.7 Placement.- 5.13 Test data elements.- 5.13.1 Test_Relation_For_D2_Wireframe.- 5.13.2 Test_Relation_For_D3_Wireframe.- 5.13.3 Test_Relation_For_Surface_Model.- 5.13.4 Test_Relation_For_Solid_Model.- 5.14 Miscellaneous.- 5.14.1 Material.- 5.14.2 Private record structures attached to CAD data.- 5.14.2.1 Record.- 5.14.2.2 Record_Type.- 5.14.3 interfacing with other data bases (not CAD data bases).- 5.14.3.1 Data_Base_Brigde.- 5.14.3.2 Data_Base_Link.- 5.15 Parametric modeling.- 5.15.1 Predefined.- 5.15.2 Integer.- 5.15.3 Integer_Expression.- 5.15.4 Real.- 5.15.5 Real_Expression.- 5.15.6 Macro.- 5.15.7 Routine.- 5.15.8 Formal_Parameter.- 5.16 Extensions of the reference mocel under consideration.- 5.16.1 Poly_Curve.- 5.16.2 Poly_Surface.- 5.16.3 Presentation of line geometry.- Levels of schema implementations.- 6.1 The geometric modeling levels.- 6.1.1 Two-dimensional wireframes.- 6.1.2 Three-dimensional wireframes.- 6.1.3 Surfaces models.- 6.1.4 Single modeling type solids.- 6.1.4.1 Pure CSG models.- 6.1.4.2 Pure Poly_Hedron models.- 6.1.4.3 Pure boundary representation models.- 6.1.5 Hybrid models.- 6.1.6 Full geometric capabilities.- 6.2 The assembly structure.- 6.2.1 No assembly structure with three levels.- 6.2.2 Full assembly structure.- 6.3 Parametric models and macros.- 6.3.1 No parametric models,no macros.- 6.3.2 Only one parametric capability.- 6.3.2.1 Parametric models only.- 6.3.2.2 Macro parametric only.- 6.3.3 Full parametric models capabilities.- 6.4 References.- 6.4.1 No external references,no library references.- 6.4.2 No external references.- 6.4.3 No library references.- 6.4.4 Full referencing capabilities.- The physical layer.- 7.1 The physical level.- 7.1.1 Tape characteristics.- 7.1.2 File transfer via computer networks.- 7.2 The metafile level.- 7.3 The alphabet level.- 7.4 Tokens of the neutral file language.- 7.4.1 Arithmetic expressions.- 7.5 The statement level.- 7.5.1 Basic statement productions.- 7.6 Rules for translating from the HDSL into BNF.- 7.7 Structure of the neutral file language.- Implementation Guidelines.- Definition of the state machine post-processor.- 8.1 The finite state approach.- 8.2 Interpreter.- 8.2.1 Begin interpretation of the neutral file.- 8.3 World.- 8.4 Entity with scope (expect World).- 8.5 Begin scope definition.- 8.6 End scope definition.- 8.7 Close entity.- 8.7.1 Close world.- 8.7.2 Close entity (expect World).- 8.8 Entity world.- 8.9 Property definition.- 8.10 Interpertation of argument lists (expect references).- 8.11 References.- 8.12 Examples of error messages.- State lists.- Relationships between operating systems and CAD.- 10.2 Data bases and libraries.- Programming rules for CAD*I processors.- 11.1 Programming language.- 11.1.1 Determination of the programming language.- 11.1.2 Requirements of the structured programming.- 11.2 Software design.- 11.2.1 Organisation of the program.- 11.2.2 Software commenting.- Programming interface.- 12.1 Mapping of HDSL data types onto Fortran.- 12.2 Application program interface routines.- Comments on pre-processors.- 13.1.1 Implementation of level 1 and level 2 per-processor routines.- 13.1.1.1 Level 1 routines.- 13.1.1.2 Level 2 routines.- 13.1.1.3 An example level 3 routine.- Comments on post-processors.- The interface of the CAD*I parser.- 15.1 Parse tree.- 15.2 Example.- Appendix A. The graphical alphabet.- Appendix B. The escape sequences.- B.1 The Latin alphabet (ISO6937).- B.2 The Greek alphabet.- B.3 The Kanji alphabet.- Appendix C. Alphabet translation into a private alphabet.- Appendix D. A neutral file for fixed format letters.- Appendix E. Examples of a CAD*I neutral files.