CAD STANDARDS

ME8691
COMPUTER AIDED DESIGN & MANUFACTURING
UNIT 3 – CAD STANDARDS
S.BALAMURUGAN
ASSISTANT PROFESSOR
MECHANICAL ENGINEERING
AAA COLLEGE OF ENGINEEERING & TECHNOLOGY

STANDARDS IN GRAPHICS PROGRAMMING
GKS, PHIGS, CORE
DXF, IGES, STEP
GRAPHICS DATA BASE
APPLICATION PROGRAM
GRAPHICS FUNCTIONS
DEVICE
DRIVER
DEVICE
DEVICE
DRIVER
DEVICE
VDI, VDM, NAPLPS
• DXF - Drawing eXchange Format
• IGES - Initial Graphics Exchange
Specification
• STEP - STandard for the Exchange of
Product model data
• GKS - Graphical Kernel System
• PHIGS - Programmer's Hierarchical
Interactive Graphics Standard
• CORE – Graphic Standard - Graphics
Standards Planning Committee (GSPC)
• NAPLPS - North American Presentation
Layer Protocol Syntax
• VDI – Virtual Desktop Interface
• VDM - Virtual Device Metafile
• ASCII - American Standard Code for
Information Interchange
ME 8691 COMPUTER AIDED DESIGN & MANUFACTURING S.BALAMURUGAN, AP/MECHANICAL, AAACET

NEED OF GRAPHICS STANDARD
• CAD / CAM System – Application program.
• It is supported with a graphics system.
• The graphic system performs all the functions related to graphic technique.
• To perform this, the graphic system is embedded in the application software.
• When this is done, the software becomes device dependent on the hardware.
• The moment hardware changes, the graphics software also needs the
changes in their source level.
Model
Requirements
Program Source
Code
Application
Software
Input / Output
Device
GRAPHICS
SYSTEM

• Impractical – Now, Today’s hardware is obsolete by tomorrow.
• NEED – To make the software device – independent. To achieve this portability, some
graphics standard were to be formed.
• GKS is an ANSI and ISO standard.
• GKS standardizes 2D graphics functionality at a relatively low level.
• The objectives of graphics standard - GKS
• To permit program portability on different hardware platforms
• Picture data portability on different hardware’s.
• Text portability
• Object database portability
• By considering this points, international organizations started working in common graphic
standard.
• It is decided that the graphic system should have two parts.
• The Kernel System = Device(hardware) independent
• Device driver (Driver) = Hardware dependent
GRAPHICS STANDARD – GKS (Graphics Kernel System)

• The kernel system act as a buffer between the application program & the specific
hardware, to ensure the independence & portability of the program.
• At point A, the application program calls the standard functions provided by the Kernel,
through Language Binding.
• This binding gives certain syntax for independent high level language.
• The language binding is provided to make best use of the corresponding language
capabilities & to handle various other syntax issues such as data types, parameter
passing & errors.
• Once the functions are invoked, they in turn call the device handler/driver functions at
point B to complete the task required by the CAD/CAM software.
Example To call “Polyline”
FORTRAN
language
CALL GPL (N, X, Y) X & Y – Arrays of coordinate values for the line
end points
C language gpolyline (n, pts) pts – list of coordinate end points
A
Model
Requirements
Program Source
Code
Application
Software
Kernel
(Core)
System
Device
Handler
/ Driver
Input / Output
Device
B
GRAPHICS SYSTEM
GRAPHICS STANDARD – GKS (Graphics Kernel System)

GKS FUNCTIONS
POLYLINES
• For drawing line segments is called polyline.
• The polyline function takes an array of X-Y
coordinates and draws line segments connecting
them.
• The attributes that control the appearance of a
polyline are:
1. Line Type 2. Line Width 3. Polyline colour
POLYMARKERS
• The GKS polymarker function allows you to draw
marker symbols centered at coordinate points
that you specify.
The attributes that control the appearance of
polymarkers are:
• Marker type - Five characters are dot, plus,
asterisk, circle, and cross.
• Marker Size
• Polyline Colour
POLYLINE(N, XPTS, YPTS)
POLYMARKER(N, XPTS, YPTS)

FILL AREA - FILL AREA(N, XPTS, YPTS)
• The GKS fill area function allows you to specify
a polygonal shape of an area to be filled with
various interior styles.
The attributes that control the appearance of fill
areas are:
• Fill area interior style – Solid fill or Hatched fill
• Fill area style index - If the fill area style is
hatch, this index specifies which hatch pattern
is to be used: horizontal lines; vertical lines or
Slant lines.
• Fill area color index
TEXT
• The GKS text function allows you to draw a
text string at a specified coordinate position.
• The attributes that control the appearance of
text are:
• TEXT(X, Y, STRING). An example of the text
primitive is: TEXT(6, 3, 'A Character String')
GKS FUNCTIONS
CELL ARRAY
• The GKS cell array function
displays raster like images in a
device-independent manner.
• The cell array function takes the
two corner points of a rectangle
that you specify, a number of
divisions (M) in the X direction
and a number of divisions (N) in
the Y direction

• OpenGL - A standard programming interface for graphics.
• It was developed by Silicon Graphics, Inc. & managed by the non-profit technology
consortium, the Khronos Group.
• It is the de facto standard for high performance 3-D graphics.
• OpenGL allows the CAD system vendors to write their programs in such a way that
they do not have to worry about the specific graphics hardware users may have.
• The interface consists of over 250 different function calls which can be used to draw
complex 3D scenes from simple primitives.
• At its most basic level, OpenGL is a specification. It is simply a document that
describes a set of functions and the precise behaviors that they must perform.
• From this specification, hardware vendors create implementation (libraries of
functions) to match the functions stated in the OpenGL specification, making use of
hardware acceleration where possible.
• Hardware vendors have to meet specific tests to be able to qualify their
implementation as an OpenGL implementation.
• It is widely used in CAD, Virtual Reality, Scientific Visualization, Information
Visualization and Flight Simulation. It is also used in video games.
OPEN-GL (OPEN GRAPHICS LIBRARY)

VERTEX PROCESSING
• Input: one vertex (and attributes)
• Output: one vertex (modified)
Vertex projection
• Model View Matrix
• Projection Matrix
Assign attributes
• Color
• Texture coordinates
PRIMITIVE PROCESSING
• Input: vertices, topology
• Output: primitive
• Vertex assembly
• Viewport transformation
RASTERIZATION
• Input: primitive
• Output: fragments
• Fragment generation
• Multiple possible fragment per
pixel
• Assign color / texture / depth / ...
per fragment
• Interpolation along each primitive
OPEN-GL - GRAPHICS PIPELINE
ME 8691 CAD & M S.BALAMURUGAN, AP/MECHANICAL, AAACET

PIXEL PROCESSING
• Input: pixels
• Output: pixels
• Alpha test
• Blending test
FRAGMENT PROCESSING
• Input: fragments
• Output: pixel
Effects
• Fog
• Textures
• Images
Tests
• Stencil test
• Depth test
RASTERIZATION
• Input: primitive
• Output: fragments
• Fragment generation
• Multiple possible fragment per pixel
• Assign color / texture / depth / ... per
fragment
• Interpolation along each primitive
OPEN-GL - GRAPHICS PIPELINE
ME 8691 CAD & M S.BALAMURUGAN, AP/MECHANICAL, AAACET

STANDARD FOR EXCHANGE IMAGES
JOINT PHOTOGRAPHIC EXPERT GROUP (JPEG)
• JPEGs might be the most common file type you run across on the web, image files used
in your company's MS Word version of its letterhead.
• JPEGs are known for their "lossy" compression, meaning that the quality of the image
decreases as the file size decreases.
GIF - GRAPHICS INTERCHANGE FORMAT
• GIFs are most common in their animated form.
• This is a common file type for web projects where an image needs to load very quickly.
RASTER IMAGES VECTOR IMAGES
• Images are constructed by a series
of pixels, or individual blocks, to
form an image.
• Images are far more flexible. They are
constructed using proportional formulas
rather than pixels.
• JPEG, GIF, and PNG are all raster
image extensions.
• EPS, AI and PDF are perfect for creating
graphics that require frequent resizing.
• Every photo you find online or in
print is a raster image
• Your logo and brand graphics should have
been created as a vector, and you should
always have a master file on hand
PDF - Portable Document Format, EPS - Encapsulated Postscript, AI - Adobe Illustrator Document

PNG - PORTABLE NETWORK GRAPHICS
• PNGs are amazing for interactive documents such as web pages, but are not suitable
for print.
• PNGs are "lossless," meaning you can edit them and not lose quality, they are still low
resolution.
• The reason PNGs are used in most web projects is that you can save your image with
more colors on a transparent background. This makes for a much sharper, web-quality
image.
WINDOWS BITMAP FORMAT (BMP)
• The MS-Windows standard format is BMP and was developed as a device-independent
bitmap (DIB) format that will allow Windows to display the bitmap on any type of display
device.
TAGGED IMAGE FILE FORMAT (TIFF/TIF)
• A TIF is a large raster file that doesn't lose quality.
• This file type is known for using "lossless compression," meaning the original image
data is maintained regardless of how often you might copy, re-save, or compress the
original file.
• Avoid using this file type on the web, it can take forever to load.
• TIFF files are also commonly used when saving photographs for print.
STANDARD FOR EXCHANGE IMAGES

NEED FOR CAD STANDARDS
• The rise of global efforts has created the need for sharing information among
vendors involved in multi-disciplinary projects.
• One organization - Developing a CAD model.
• Another organization - Performs analysis work on the same model
• At the same time a third organization - Manufacturing the product.
• Data transfer fills the need to satisfy each of these functions in a specific way.
• We need to understand, how engineering model data is delivered today to
manufacturers and suppliers.
• Each software employs its own system specific data structure to store the
model.
• All these problems stress towards the need to have a method of data exchange
between various software's.

Product
Design
(CAD)
Engineering
and Analysis
(CAE)
Customer
Requirements
Product
Databases
Manufacturing
Databases
Materials
Planning Procurement
Installation
and
DistributionFabrication, Assembly & Test Operations
Product
Information
Management
Product Design
Manufacturing
Engineering
Supply Management
Customer
Suppliers
Marketing
Process
Planning
Neutral I/F
Neutral I/F
PRODUCT DATA MANAGEMENT
CAD data is used throughout
the organization

CAD DATABASE INFORMATION
• Transferring data between dissimilar CAD / CAM systems must ensure that the complete
production description is effectively transferred.
• SHAPE DATA
• Both Geometrical & Topological Information.
• Entity Attributes – Colors, Line type, Fonts, Layer are part of geometrical
information.
• NON-SHAPE DATA
• This includes graphics data such as shaded images, model measuring unit,
Resolution of storing the database.
• MANUFACTURING DATA
• It includes information related to the final manufacture of the design, e.g. tooling, NC
tool paths, tolerancing, process planning, and bill of material.
• DESIGN
• This information is useful for analysis. Information such as Mass property,
geometrical properties can be generated using the design data.
• METADATA
• It is the information (e.g. time stamps and the owner of the data) about a particular
data (e.g. geometric data).

• Necessity to translate drawings created in one drafting package to another often
arises.
• One method is to write direct translators from one software to another, which has to
be produced by system developer.
EXCHANGE OF MODELING DATA
CREO
AUTOCADANSYS
DIRECT DATA TRANSLATOR
• If we have three software packages we
may require six translators among them.
• This will necessitate a large number of
translators.
INDIRECT DATA TRANSLATOR
• A neutral file independent of any specific CAD/CAM is
developed.
• Indirect exchange is more suitable, as it protects against
system becoming out of date & eliminate system
supplier dependence.

EVOLUTION OF DATA EXCHANGE STANDARDS
• The syntax of the neutral file is
governed by well defined standards.
• Based on these standards, CAD/CAM
software developing companies
provide the necessary interface to
convert their data formats into neutral
formats, or to read neutral formats &
convert it to their format of data.
SHAPE BASED FORMAT(DXF, IGES)
• Initially, the primary goal of exchange
was the geometrical data.
PRODUCT DATA BASED FORMAT (STEP)
• As time progressed, it was realized
that besides the shape data,
production data played an important
role.
• This resulted in the exchange of all
the CAD information’s.

DRAWING EXCHANGE FORMAT (DXF)
• Shape Based Format
• The DXF format has been developed and supported by Autodesk, on December 1982,
with AutoCAD 1.0 for use with the AutoCAD drawing files.
• It enables data interoperability between AutoCAD and other programs.
• DXF file is in ASCII form. (American Standard Code for Information Interchange)
STRUCTURE OF DXF FILE
HEADER SECTION
• General information about the drawing.
• Each parameter has a variable name & an associated value.
• These variables are set with various commands & represent the type of information
displayed by the STATUS command.
• System setting such as dimension style & layers.
CLASSES SECTION
• Holds the information for application-defined classes whose instances appear in the
BLOCKS, ENTITIES, and OBJECTS sections of the database.
• It does not provide sufficient information to allow interoperability with other programs.

TABLES SECTION
• It contains several tables, each of which contains a variable number of table entries.
• Table names are always in the uppercase characters.
• The LTYPE table will always come before the LAYER table.
• Each table is introduced with a 0 group with label TABLE.
• This is followed by a 2 group, identifying the particular table (VPORT, LTYPE, LAYER,
STYLE, VIEW, DIMSTYLE, UCS or APPID)
BLOCKS SECTION
• It contains all the Block definitions.
• This section contains the entities that make up the Blocks used in the drawing.
• Also it includes additional blocks generated by the HATCH command.
• All entities in the Blocks section appear between BLOCK & ENDBLK entities.
Application ID (APPID) table Layer (LAYER) table
Block Record (BLOCK_RECORD) table Line type (LTYPE) table
Dimension Style (DIMSTYPE) table Text style (STYLE) table
User Coordinate System (UCS) table View (VIEW) table
Viewport configuration (VPORT) table
STRUCTURE OF DXF file

ENTITIES SECTION
• Entity items appear in both the BLOCK & ENTITIES sections of the DXF file.
• The appearance of entities in the two sections is same.
• Each entity begins with a 0 group.
• Every entity contains an 8 group that gives the name of the layer on which the entity
resides.
• Each entity have thickness, line type or color information associated with it.
Entity = Example – Circle, Ellipse, Leader
THUMB NAIL IMAGE SECTION
• It contains the preview image of the DXF file.
• This section exists only if a preview image has been saved with the DXF file.
LIMITATIONS
• It does not support application specific CAD elements.
• Complex DXF file can become large in size.
STRUCTURE OF DXF file

• Shape based file format
• This file format was mainly developed by the efforts of Boeing Company,
General Electric company & National Bureau of Standards (NBS).
• IGES is mainly to address the exchange of shape & non-shape based data.
• It is one of the first standards to be developed to address the concept of
communication data among dissimilar CAD /CAM systems.
• Applications supported by IGES include traditional engineering drawings,
models for analysis, and other manufacturing functions.
IGES
INITIAL GRAPHICS EXCHANGE SPECIFICATION
• IGES version 1.0 was released in 1980
• It converts the CAD model into neutral file.
• Conversion is done by preprocessors
inbuilt in the software, which converts the
native database into IGES format.
• Post Processor converts IGES files to
native database.

STRUCTURE OF IGES FILE
FLAG SECTION
• This is an optional section & is used only with compressed ASCII & Binary format.
• It is a single line that comes before the start section of the file with the character “C”
in column 73 to identify the file as compressed ASCII.
START SECTION
• It contains human readable line – Introduction section of the file.
• Information such as the names of the sending (Source) & receiving (Target) systems
with a brief description of the product being converted is written in this section.
• Column 73 – Section code “S”
GLOBAL SECTION
• This section contains details about the product, organization, software, date etc.
• This section includes information describing the preprocessor & the information
needed by the post processor to interpret the file.
• The global section shows the path of the file, File name, Units etc.
• Column 73 – Section code “G”

DIRECTORY ENTRY SECTION - Column 73 – Section code “D”
• This section consists of all the entities defined in the file.
• Each entity occupies two 80 character records.
• First field – Entity Type Number, Second field – It contains a pointer to the parameter
data entry for the entity in the next section.
• 110 – Straight line - 1P0000001 – By end points (0,5,0) to (0,0,0)
• 100 – Circular arc – Arc defined by Center point, Start point & End point
PARAMETER DATA SECTION - Column 73 – Section code “P”
• This section contains the actual data defining each entity.
• Example – Straight line is identified by two end points – 6 Coordinates. (1point–3 Co.)
• Comma – Used to separate parameter
• Semicolon – Used as a record delimiter, Specified in the global section.
TERMINATE SECTION - Column 73 – Section code “T”
• This is a single record which specifies the number of records in each of the preceding
sections for error checking.
• Ex - S0000002 – Two lines in start section, G0000004 – 4 lines in global section.
STRUCTURE OF IGES FILE

SUBSECTIONS OF IGES FILE

IGES FILE - ENTITIES
This drawing Contains
• Two POINT (Type 116)
• Two CIRCULAR ARC (Type 100)
• Two LINE (Type 110).
MSRIT
100: circular arc
108: plane
110: line
116: point
120: tabulated cylinder
134: node
158: sphere
184: solid assembly
190: plane surface

Standard for the Transfer & Exchange of Product model data - STEP
• Product Data Based Format
• To ensure complete exchange of shape, non-shape, design & manufacturing data.
• This kind of transfer used to the entire life cycle of a product development such as
design, manufacturing, quality assurance, testing & support.
• For industrial automation, the required product data must contain all the four basic
information of CAD file.
• PDES – Product Data Exchange using STEP.
• STEP – the central unit of data exchange is the application, which in turn contains
many entities.
• The Structure of STEP file has three basic layers.
APPLICATION LAYER
• This is the interface between the user & PDES.
• It contains the complete description & information of the various application areas.
• Various discipline models form the core of the application layer.
• The descriptions & information's are expressed within the PDES as reference models.

LOGICAL LAYER
• First, discipline layer is developed in the
application layer.
• It contains a qualified discipline mode, which
is written for applications defined in the
previous layer.
• Then it is used to develop the logical layer.
• This layer presents consistent & computer
independent information of the resource
models whose data to be exchanged.
• Generic & Specific application data are
identified. It is important to ensure that no
redundant or repetitive data is reproduced.
• A global model is created to represent all
discipline specific & generic entities.
• The global model is used to validate the
correctness of the correspondence between
application layer & Logical layer.
• Once the global model is developed, the
Data Specification Language(DSL) is used
to generate an information model.
• DSL , Expressing the binary information of the global model into Text form. (Readable)

PHYSICAL LAYER
• This layer deals with the structure & format of the data within the file,
• Main objective is to maintain efficiency in the file size to avoid the processing time.
• The user on Source end defines the product data in the form of a discipline model.
• The preprocessor use this discipline to produce a 3 layer data exchange PDES file.
• The post processor process this 3 layer PDES file, & it interprets the discipline model
& converts it into product data.
• This product data is used in the target end.
Three Layer
Data
Exchange
(PDES)
Product
Data
Discipline
Model
Preprocessor Postprocessor
Discipline
Model
Product
Data
SOURCE
TARGET

CALS
Continuous Acquisition and Life Cycle Support
• CALS developed for United States Ministry of Defense.
• US defense was looking for ways to develop the electronic transfer of
information.
• To transfer the technical information between separate IT systems, this
standard was developed.
• This standard was designed to be so broad, to transfer every kind of
information, including text and graphics, could be moved effectively between
different systems.
• CALS contains several different standards:
• SGML standard - Standard Generalized Markup Language
• IGES format for the transfer of CAD files
• EDI (Electronic Data Interchange) for the transmission of
commercial documentation.
• In spite of its background, the standard has also gained a foothold in the
civilian world, especially among large-scale international enterprises.

• In the first stage, data transfer
takes place according to
neutral transfer standards.
• In the second stage, a large
database is created for the use
of different parties within the
information network.
• SGML standard - Standard
Generalized Markup Language
• This standard is mainly used to
describe the contents and
structure of documents.
• document description language
• separates content from structure
(formatting)
• uses “tags” to define headings,
sections, chapters, etc.
• HTML is based on SGML
CALS
Continuous Acquisition and Life Cycle Support
Traditional Data Transfer Model & Stage 1 & 2 of CALS

LEVELS OF COMMUICATION STANDARDS
GKS, PHIGS, CORE
DXF, IGES, STEP
GRAPHICS DATA BASE
APPLICATION PROGRAM
GRAPHICS FUNCTIONS
DEVICE
DRIVER
DEVICE
DEVICE
DRIVER
DEVICE
VDI, VDM, NAPLPS
• DXF - Drawing eXchange Format
• IGES - Initial Graphics Exchange
Specification
• STEP - STandard for the Exchange of
Product model data
• GKS - Graphical Kernel System
• PHIGS - Programmer's Hierarchical
Interactive Graphics Standard
• CORE – Graphic Standard - Graphics
Standards Planning Committee (GSPC)
• NAPLPS - North American Presentation
Layer Protocol Syntax
• VDI – Virtual Desktop Interface
• VDM - Virtual Device Metafile
• ASCII - American Standard Code for
Information Interchange

WEB AND INTERNET STANDARDS
• HYPERTEXT MARKUP LANGUAGE (HTML)
• used to describe web pages
• based on SGML
• VIRTUAL REALITY MODELLING LANGUAGE (VRML)
• VRML is a language for describing three-dimensional image sequences
and possible user interactions to go with them.
• Using VRML, you can build a sequence of visual images into Web settings
with which a user can interact by viewing, moving, rotating, and otherwise
interacting with an apparently 3-D scene.
• For example, you can view a room and use controls to move the room as
you would experience it if you were walking through it in real space.
• SGML standard - Standard Generalized Markup Language
• This standard is mainly used to describe the contents and structure of
documents.
• document description language
• separates content from structure (formatting)
• uses “tags” to define headings, sections, chapters, etc.
• HTML is based on SGML

CAD STANDARDS

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