ME 6501 Computer Aided Design A.R Engineering College Department of Mechanical Engineering ME 6501 Computer Aided Design Presented by Er.J.Sankar, Assistant Professor, Dept Of Mechanical Engineering, A.R Engineering College.

Unit-1 FUNDAMENTALS OF COMPUTER GRAPHICS Product cycle- Design process- sequential and concurrent engineering- Computer aided design – CAD system architecture- Computer graphics – co-ordinate systems- 2D and 3D transformations- homogeneous coordinates - Line drawing - Clipping- viewing transformation

Product Cycle

Design Process

Sequential Engineering The process of marketing, engineering design, manufacturing, testing and production where each stage of the development process is carried out separately, and the next stage cannot start until the previous stage is finished. The information flow is only in one direction.

Concurrent Engineering concurrent engineering involves the formation of cross- functional teams, which allows engineers and managers of different disciplines to work together simultaneously in developing product and process design.

Difference between Sequential engineering and Concurrent engineering Sequential engineering is the term used to describe the method of production in a linear format. The different steps are done one after another. After it is completed it is left alone and everything is concentrated on the next task. Time Consumption for marketing is more The concurrent engineering is a non-linear product or project design. several teams within an organization work simultaneously to develop new products and services. different tasks are tackled at the same time, and not necessarily in the usual order. Time consumption for marketing is less

Computer Aided Design computer systems to assist in the creation, modifications, analysis and optimization of a design. Activities of the CAD process are mass properties, finite element analysis, dimensioning, tolerancing, assembly modeling, generating shaded images, and documentation and drafting. The CAD process and its tools utilize three disciplines: Geometric Modeling, Computer Graphics, and Design

CAD system architecture Hardware Data Software

Basic Structure of a CAD system

I/O devises of CAD system

Graphics Display CRT 1.Vacuum tube provide high vacuum & voltage 2.Electron beam focoused to the screen through focousing system and deflection systems. 3.The incident electron beam on phosphor coatings results the illumination due to the energy transfer from electron into phosphorous.

Types of Graphic Display based on Scan technology Random Scan The screen is not scanned in a particular order. Raster Scan The screen is scanned from left to right, top to bottom all the time to display graphics.

Flat Screen CRT Comfortable look at from wide viewing angles. Fewer reflections Offers larger viewable area than an equivalent size curved CRT. Well suited for touchscreen.

Schematic diagram of a flat panel display

Digital flat panel display A backlight panel is used to generate light. The display uses two grooved glass panels and two polarizing filters, forming two compatible pairs. The vertical pair has a vertical polarizing filter and a vertically grooved glass panel next to it. Similarly, the horizontal pair has a horizontally grooved glass panel and a horizontal polarizing filter next to it. Voltage is applied between the two glass panels to charge the molecules between the glass panels to change their alignment from vertical to horizontal. light is polarized vertically via the vertical filter, therefore passing through the glass panel with vertical grooves and the molecules next to it. As the light passes through the molecules, it gets twisted.

When the light reaches the second glass panel, it would have been oriented perfectly horizontal. It thus passes through the horizontal polarizing filter and causes the display to show the image. The color filter is used to generate colors. Three cells are used in the filter, one for each of the red, green, and blue signals. The color effect is created by controlling the level of brightness between all light and no light passing through. The amount of twisting of LCD molecules controls the display sharpness. The more the molecules are twisted, the better the display contrast. Twisted Nematic (TN) twists the molecules 90 percent to improve contrast. STN (super TN) twists the molecules by 140 percent to make the contrast even better.

Pixel Term that comes from the words Picture Element (PEL). A pixel (px) is the smallest portion of an image or display that a computer is capable of printing or displaying. You can get a better understanding of what a pixel is when zooming into an image as seen in the example to the right.

Pixels in Mobile Camera

Co-ordinate system Model Coordinate system Working coordinate system Screen coordinate system

Model Coordinate System (MCS) The model coordinate system is defined as the reference space of the model with respect to which all the model geometrical data is stored. it is a cartesian system which forms the default coordinate system used by a software program. The MCS is the only coordinate system that the software recognizes when storing or retrieving graphical information in or from a model database. Many existing software packages

2D Translation A Point (x,y) Is translated to (x’, y’) by a distance (dx, dy) x’=x + dx y’=y + dy In a homogeneous coordinates, we represent a point (x,y) by a column vector P= 𝑥 𝑦 1 similarly P’= 𝑥 ′ 𝑦 ′ 1 then the translation matrix can be achieved by matrix multiplication, 𝑥 ′ 𝑦 ′ 1 = 1 0 𝑑 𝑥 0 1 𝑑 𝑦 0 0 0 𝑥 𝑦 1 T(dx,dy) = 1 0 𝑑 𝑥 0 1 𝑑 𝑦 0 0 0 , the translation matrix

Rotation in Two-Dimensions

Example Problem

2D Scaling A Point P(x,y) is scaled to P(x’, y’) by a scaling Vector (sx,sy) x’=sxx y’=syy In a homogeneous coordinates, Scaling can be achieved by 𝑥 ′ 𝑦 ′ 1 = 𝑠 𝑥 0 0 0 𝑠 𝑦 0 0 0 1 𝑥 𝑦 1 S(sx,sy) = 𝑠 𝑥 0 0 0 𝑠 𝑦 0 0 0 1 , the Scaling matrix equation.

3D Translation, Scaling Translation T(dx,dy,dz) = 1 0 0 𝑑 𝑥 0 1 𝑂 𝑑 𝑦 0 0 0 0 1 0 𝑑 𝑧 1 Scaling S(sx,sy,sz) = 𝑠 𝑥 0 0 0 0 𝑠 𝑦 0 0 0 0 0 0 𝑆 𝑧 0 0 1

3D Rotation

CLIPPING Clipping is the process of determining the visible portions of a drawing lying within a window. In clipping each graphic element of the display is examined to determine whether or not it is completely inside the window, completely outside the window or crosses a window boundary. Portions outside the boundary are not drawn. If the element of a drawing crosses the boundary the point of inter-section is determined and only portions which lie inside are drawn.

Line Drawing Straight line segments are used a great deal in computer generated pictures. The following criteria have been stipulated for line drawing displays : i. Lines should appear straight ii. Lines should terminate accurately iii. Lines should have constant density iv. Line density should be independent of length and angle v. Line should be drawn rapidly The process of turning on the pixels for a line segment is called vector generation. If the end points of the line segment are known, there are several schemes for selecting the pixels between the end pixels. One method of generating a line segment is a symmetrical digital differential analyzer (DDA).

DDA ALGORITHM The digital differential analyzer generates lines from their differential equations. The DDA works on the principle that X and Y are simultaneously incremented by small steps proportional to the first derivatives of X and Y. In the case of a straight line the first derivatives are constant and are proportional to DX and DY, where D is a small quantity. To draw a straight line from connecting two points (2, 7) and (15, 10) X1 = 2, X2 = 15 abs(X2 – X1) = 13 Y1 = 7, Y2 = 10 abs(Y2 – Y1) = 3 Length = 13 X incr = X2-X1/Length = 13/13 = 1 Y incr = y2-y1/length = 3/13 = 0.23

Initial values of X and Y are X = 2.5 Y = 7.5 Plotting a Line Pixel Values