This document discusses various CAD standards including: 1. Graphic standards like GKS and OpenGL that allow for portability of geometric models between hardware and software. 2. Data exchange standards like IGES and STEP that define neutral formats for transferring CAD data between different systems. 3. Communication standards like LANs and WANs that enable the transfer of CAD data between networked computer systems. The standards aim to facilitate interoperability for CAD/CAM data by providing common languages and specifications for graphics, file formats, and network communication.

1. UNIT 3
CAD STANDARDS

2. Content
• Standards for computer graphics
• Graphical Kernal System (GKS)
• Standards for exchange image
• Open Graphics Library (open GL)
• Data exchange standards
• IGES, STEP, CALS, etc
• Communication standards

3. Purpose of CAD standard
• The transfer of data between dissimilar CAD/Cam system must
embrace the complete description of a product stored in its
database.
• Four types of modeling data make up this description
Shape data – consists of geometrical and topological data
Non-shape data – include shaded image and measuring units of data
base
Design data – FEM/FEA, engineering analysis
Manufacturing data – include tolerencing and bill of materials

4. Types of translators
i) Direct Translators
It entails translating the modeling
data directly from one native
format to another. It require a
knowledge of both native
formats
Direct translator convert data
directly in one step.

5. Types of translators
i) Indirect Translators
It converts the modeling data directly
from one native format to neutral
format that all CAD/Cam system can
interpret and understand.
Each translation system has its own
pair of translator to translate data to
and from the neutral format

7. Organization of a typical CAD/CAM
structure with graphics standards

8. DATABASE MANAGEMENT
• Database is a collection of data at a single location to be used by
various people for different applications.

9. OBJECTIVES OF DATABASE
• It provides security
• It shares the data among users
• It incorporates the changes quickly and effectively
• It improves accuracy and integrity of data
• It reduces the cost of storage and retrieval of data
• It reduces or eliminates the redundant data

12. STANDARDS FOR COMPUTER
GRAPHICS
• Need for graphic standards
• There is a need for portability of the geometric model among different
hardware platforms.
• Where there is a situation to exchange drawing database among software
packages.
• There is a need for exchanging graphic data between different computer
systems.

13. CLASSIFICATION OF CAD
STANDARDS
• Graphic and computing standards
• Data exchange standards
• Communication standards

14. GRAPHIC AND COMPUTING
STANDARDS
• Aim for graphics standardisation
• To allow the transfer of graphic data between two or more different companies
which may have completely different CAD systems.
• To control all types of graphic devices such as plotters and display devices in a
consistent manner.
• To be small enough for a variety of programs.

15. GKS (GRAPHICS KERNEL SYSTEM)
• Series of commands used for graphical operations.
• Number of elements that may be drawn in an image is known as
graphical primitives.

16. Representation of levels in graphics standards
CAD entities
Graphics
primitives
Image bitmap
CAD data exchange
standards – IGES,
STEP
Device independent
picture description –
Metafile, e.g, CGM
Bitmap standards –
e.g, GIF, TIFF
CAD representation Level Equivalent standards

21. STANDARDS FOR EXCHANGE
IMAGES
• The purpose of GKS and other similar standards is to allow graphics
to be drawn on a display device by an application program.
• The model is converted by the series of graphics primitives, and these
are then displayed on the screen using the graphics procedures,
typically by setting the values of the pixels in a rectangular raster
array.
• The raster array is represented by a region of computer memory is
known as bitmap.

24. OPEN GRAPHICS LIBRARY
• Silicon Graphics Inc., developed the software interface for
graphics hardware known as Open Graphics Language (Open GL).
• Open GL Comprises a set of several hundred procedures and
function that allow a programmer to specify the objects and
operations involved in the production of colour graphical image .
• OpenGL (Open Graphics Library)is a cross-language, multi-
platform application programming interface (application program
interface-API) for rendering2D and 3D vector graphics. The API is
typically used to interact with a graphics processing unit (GPU), to
achieve hardware-accelerated rendering.

25. • Open GL does not require high performance display hardware to be
present, but it require a frame buffer memory that stores the raster
display bitmap.
• Open GL draws directly in to the frame buffer but also allows the use
of multiple buffer where for e.g., one buffer is displyed while second
is being updated.

26. Data exchange standards
• CAD data exchange involves a number of software technologies and
methods to translate data from one Computer-aided design system
to another CAD file format.
• The recent decades, the data transfer of data between the system
has been made possible by the neutral format of data exchange.

28. Development of Data Exchange Format
• The significant work in data exchange was started in 1979 of an Initial
Graphics Exchange Specification (IGES) which was supported by US
national Bureau of standards.
• Boeing and GE were chosen due to their prior experience in
developing data exchange formats – Boeing with its CIIN (CAD
Integrated Information Network)
• IGES owned very good support among the CAD users and vendors.

30. IGES has three types of entity:
• Geometric – it defines the product shape and include curves, surface
and solids
• Annotation – it included various types of dimensions (linear, angular,
ordinate), centre line , notes, general labels, symbols and cross
hatching
• Structure – it includes views, drawing , attributes( such as line and
text fonts, colors and layers), properties (mass), subfigures and
external cross reference entities (for surface and assemblies)

34. IGES

37. Error handling
• While importing IGES file, error handling is very important
• There are two major error sources when processing IGES files
Program errors in the processors
Misinterpretation of the IGES standard itself.
• The way an IGES processor report error is – the processor should
report the entity type, number of unprocessed entries, reason for un-
processing and other relevant database information of these
unprocessed entities.
• IGES should also report any invalid or missing data encountered in
reading IGES files especially those that were edited.

38. STEP
• STEP ( standard for Exchange of Product Data) is an exchange for
product data in support of industrial automation

41. CALS
• Continuous Acquisition and Life cycle support is CALS.
• CALS was originally called Computer Aided Acquisition and Logistics
Support.

42. COMMUNICATION STANDARDS
• Data exchange depends not only on the compatibility of the
applications data formats between the communicating systems.
• LAN (Local area networks)
• WAN (Wide area networks)

43. LAN

44. WAN