Data exchange format and types

1. CAD Data Exchange Format
Prof. R.B.Chadge

2. Data Exchange between
CAD/CAM/CAE System

3. • Fundamental incompatibilities among entity
representations
• Complexity of CAD/CAM systems
• The varying requirements of users
• Restrictions on access to proprietary database
information
• Rapid pace of technological change
Driving Forces for CAD/CAM Data
Exchange

4. • Shape data: both geometric and topological
information, part or form features. Fonts, colour,
annotation are considered part of the geometric
information.
• Non-shape data: graphics data such as shaded images
and model global data as measuring units of the
database and the resolution of storing the database
numerical values.
Requirements for the Exchange

5. • Design data: information that designers generate from
geometric models for analysis purposes. Mass
property and finite element mesh data belong to this
type of data.
• Manufacturing data: information as tooling, NC tool
paths, tolerancing, process planning, tool design, and
bill of materials (BOM).
Requirements for the Exchange

8. CAD File Formats
• Every CAD package stores information internally in a
format that is best suited for that package. When the
user is done, this information is written to files on the
hard drive.
• These proprietary formats can only be read by the
specific program (and version of software), and are
virtually useless to other programs.
• For most modern engineering applications it is
necessary to be able to transfer CAD models between
dissimilar computer programs.

9. • Standard file formats are the best method for storing
and transferring CAD geometries (and other
information) between dissimilar programs.
• Files are mainly stored on disks as ASCII, or binary
with a structure that has been agreed upon by
organizations that represent various interest groups in
the CAD/CAM sectors.
• When standard formats are used data should be easily
transported between systems. Although beware, some
vendors do not conform fully to these standards.
CAD File Formats

10. • The basic structure of programs using standard files is
shown below
CAD File Formats

11. Exchange Methods

12. • Every CAD system uses its own proprietary data
format
• Design data must be converted from one format to the
other
PROBLEMS

13. Direct Translation between CAD
Systems
• Need a translator from
every CAD package to
every other
• For 4 CAD packages,
need 6 translators
• For 6 CAD packages,
need 16 translators.

14. • To address the problem, many standards for CAD
data exchange have been developed.
• CAD systems can import and export to many of these
standard formats.
Data Exchange Standards

15. Evolution of Data Standards

16. • Translation using IGES is unreliable
– geometry is corrupted
– much cleanup required after translation
• Translation using STEP is not widespread
– STEP translators only recently available
• Existing translators lose information
– parametrics and constraints
– features and history trees
Current Situation

17. • To avoid data translation problems, many companies
have standardized on a single CAD system
• Ford
– all suppliers must use I-DEAS
• Chrysler
– all suppliers must use CATIA
• General Motors
– all suppliers must use Unigraphics
Short-term Solutions

18. • To deal with all three automakers, you must support
I-DEAS, Unigraphics and CATIA.
• For small companies, this is very difficult.
New Problem for Suppliers

19. • A better solution is development of reliable data
exchange standards, using a neutral interface.
A Better Solution

20. Neutral Interface

21. • The interface must be capable of handling all
manufacturing data
• There should be no information loss (maintain the
semantics during conversion)
• The system must be efficient to be capable of
handling the real-time requirements of manufacturing
• The system should be open-ended to permit
extensions or contractions
Requirements of an Interface

22. • The system should be adaptable to other standards
• The system must be independent of the computer and
architecture used
• It must be possible to form application-oriented
subsets of the standard to reduce costs
• The interface must be upward and downward
compatible in a hierarchical control structure.
• Test procedures must be provided to verify
effectively.
Requirements of an Interface

23. • Formatted ASCII file format
• Supports many 2D and 3D CAD entities
• Has gone through several versions since 1980
• Widely supported
Initial Graphics Exchange Specification
(IGES)

24. • Many incompatible “flavors”
• Unreliable translation, particularly for complex
geometry
• No formal information modeling basis
• Insufficient support for conformance testing
Problems with IGES

25. • Uses a formal model for data exchange
• Information is modeled using the EXPRESS language
• EXPRESS has elements of Pascal, C, and other
languages
STEP (Standard for the Exchange of
Product Model Data)

26. • It contains constructs for defining data types and
structures, but not for processing data
• EXPRESS describes geometry and other information
in a standard, unambiguous way
STEP (Standard for the Exchange of
Product Model Data)

27. STEP Architecture

28. • Introductory
• Description methods
• Implementation methods
• Conformance testing methodology and
framework
• Integrated resources
• Application protocols
• Abstract test suites
• Application interpreted constructs
Classes of STEP Parts

29. • STEP has been under development for many years,
and will continue for many more
• Over a dozen STEP parts have been approved as
international standards
• Many others are under development
Status of STEP

30. • Developed by US Department of Defense
• Prescribes formats for storage and exchange of
technical data
• Technical publications an important focus
Continuous Acquisition and Life-cycle
Support (CALS)

31. • Standard Generalized Markup Language (SGML)
– document description language
– separates content from structure (formatting)
– uses “tags” to define headings, sections, chapters,
etc.
– HTML is based on SGML
• Computer Graphics Metafile (CGM)
– vector file format for illustrations and drawings
• IGES
– also used for illustrations
Important CALS Standards

32. • Standards
– Joint Photographic Expert Group (JPEG)
• Proprietary
– Graphics Interchange Format (GIF)
– Windows bitmap format (BMP)
– Zsoft file format (PCX)
– Tagged Image File Format (TIFF/TIF)
– Targa file format (TGA)
Common Formats for Bitmap Images

33. • Hypertext Markup Language (HTML)
– used to describe web pages
– based on SGML
• Virtual Reality Modelling Language (VRML)
– standard for description of 3D interactive
environments and worlds
– downloaded and displayed in a web browser
– well suited to sharing of CAD data
Web and Internet Standards

34. • DXF
– de facto standard published by AutoDesk
(AutoCAD)
• STL
– 3D file format used as input for Stereolithography
• SAT
– solid model file format used by ACIS-based CAD
systems
Other CAD File Formats

35. Some Graphics formats are intended for graphical
display:
• GIF - (Graphics Interchange Format) A compact
graphic format
• JPG - (Joint Photographic experts Group) A
compressed format
• MPEG - (Motion Pictures Experts Group)
Compressed Animation
Graphics Formats

36. Some graphics formats are intended for output on
hardcopy devices:
• HPGL - Hewlett Packard Graphics Language - An
ASCII language devised to drive pen plotters
• PostScript - A VERY popular graphics format which
typically drives laser printers, but can also be
displayed on devices like color screens
Graphics Formats

37. Some types are:
CGM - A US defense department product, related to
polygon modeling
CIF - For Integrated Circuit Design by layered polygon
definition
DMC - Digital Mapping for Customers - for
transmitting maps
DXF - Primarily developed by Autodesk (for Autocad)
to transfer geometry using ASCII definitions
CAD Formats

38. • IGES (Initial Graphics Exchange Specification)
• EDIF - Electronic Design Interchange Format
supports VLSI design, and is expected toincorporate
Circuit Boards soon
• IISF - A format Developed by Intergraph for their
CAD systems
• SET - Standard d'Echange et de Transfert - Made to
be more compact than IGES
CAD Formats

39. • STEP and PDES (Standard for the Exchange of
Product model data and Product Data Exchange
Specification) An attempt to model other attributes of
a product, in addition to geometry, such as
tolerancing. This is the emerging standard, but it is
not widely available yet.
• VDA-FS (DIN 66301) A German approach for
modelling surfaces
• VDA-IS - A German subset of IGES for the auto
industry
• UNV - Ideas Universal File
CAD Formats

40. • A device independent format is based on public
standards that are controlled by non-commercial
bodies.
• Examples of these include
– STEP (Standard for Exchange of Product Data)
– SET (Standard Exchange Transfer)
– PDES (Product Data Exchange Specification)
– IGES (Initial Graphics Exchange Specification)
Standard Formats

41. • IGES was first developed by the National Bureau of
Standards, Boeing Corporation, and General Electric
Corporation and published by the National Bureau of
Standards in 1980.
• Initially the only data that could be exchanged were
basic entity types such as points, lines, arcs, and
circles.
• September 1981, IGES version 2.0 was approved by
the American National Standards Institute as ANSI
standard Y14.26M for CAD/CAM communications.
IGES (Initial Graphics Exchange
Specification)

42. • More recent versions of IGES contain the ability to
transfer constructive solid geometry and boundary
representations of solid models.
• The IGES can be in either binary or ASCII format. In
ASCII the file is easy to read and modify by hand but
it tends to be larger.
IGES (Initial Graphics Exchange
Specification)

43. (Product Data Exchange Specification/Standard for the
Exchange of Product model data)
• PDES (using STEP) is the result of an international
effort to develop a standard product design standard.
• This format attempts to incorporate all aspects of
product modeling including:
1. geometry (B-Rep, CSG, Features)
2. Tolerances
3. electrical/electronics
PDES/STEP

44. 4.function information
5. process plans etc.
PDES/STEP