1. PREPARED BY: SAMERA BINTI SAMSUDDIN SAH
ERT 249 Computer Aided Design (CAD) For Biosystem Engineering
3-D PROJECTION
PREPARED BY: SAMERA BINTI SAMSUDDIN SAH

2. 3D PROJECTION
Three different types of 3-D projections are available in most CAD software:
isometric,
trimetric, and
perspective.
These three views of a cube are shown in figure below.

3. In all three cases, these 3-D projections represent all three dimensions of the cube in a single planar image.
Although it is clear in all three cases that the object is a cube, each type of 3-D projection has its advantages and disadvantages.

4. 1. ISOMETRIC PROJECTION
The isometric projection has a standard orientation that makes it the typical projection used in CAD.
In an isometric projection, the width and depth dimensions are sketched at 30° above horizontal.
This results in the three angles at the upper front corner of the cube being equal to 120°.
The three sides of the cube are also equal, leading to the term iso (equal) -metric (measure).

5. Isometric drawings work quite well for objects of limited depth.
However, an isometric drawing distorts the object when the depth is significant.
In this case, a pictorial perspective drawing is better.

6. 2. TRIMETRIC PROJECTION
In general, the trimetric projection offers more flexibility in orienting the object in space.
The width and depth dimensions are at arbitrary angles to the horizontal, and the three angles at the upper front corner of the cube are unequal.

7. This makes the three sides of the cube each have a different length as measured in the plane of the drawing; hence the name tri- metric.
In most CAD software, the trimetric projection fixes one side along a horizontal line and tips the cube forward.

8. 3. PERSPECTIVE PROJECTION
A simply perspective (pictorial perspective) projection is drawn so that parallel lines converge in the distances, unlike isometric or trimetric projections where parallel lines remain parallel.
A perspective projection is quite useful in providing a realistic image of an object when the object spans a long distance such as the view of a bridge or aircraft from one end.
Generally, small manufactured objects are adequately represented by isometric or trimetric views.

9. But the oblique projection is usually even easier to sketch.
Two types of pictorial sketches are used frequently in freehand sketching:
isometric and
oblique.
The isometric projection is often used in freehand sketching because it is relatively easy to create a realistic sketch of an object.
But the oblique projection is usually even easier to sketch.
The figure compares an isometric and an oblique projection of a cube with a hole in it.
oblique freehand sketching easier than isometric sketching.

10. Differences between 3D and 2D
Criteria 3D 2D
1. Viewing Direction
- Look at your object from an angle
- Look straight down on the drawing plane
2. Object Created
- have depth
- No depth
3. Command related
- 80 AutoCAD commands related primarily to 3D
- however, are also useful in 2D
4. Constructing object
- Yes
No.
Drawing picture from different viewpoints

11. Some Frequently used 3D Terms
3D objects made in AutoCAD called models
2D work referred to as drawing/drafting
Model

12. Some Frequently used 3D Terms
Object by its edges only
Wireframe cannot hide object that are behind them
Hole has no meaning in a wireframe model because there is nothing in which to make a hole
1. Wireframe Model

13. 2. Surface Model Surface model; solid + empty shell
Surface model often use wireframe models as a frame for their surfaces
Surface model; part wireframe + part surface
2. Surface Model

14. 3. Solid Model Wireframe, surface model & computer-calculated mass;
eg: volume, centre of gravity, mass moment of inertia
Solid models look like wireframe unless a hidden line removal command is in effect
3. Solid Model

15. Shaded, realistic-looking picture of a surface solid model is called a rendering
Two type:
Grayscale rendering
Fully capable of colour rendering
4. Rendering

16. Show design more clearly Closer to representing real object than a 2D
Reasons For Using 3D
Good for verifying design as well as for use in presentation and documentation as well.
Show design more clearly
Closer to representing real object than a 2D

17. 3D Capabilities of AutoCAD
1. AutoCAD has complete 3D coordinate system for specifying points and drawing objects anywhere in space
2. To assist in point input and for working in local area, AutoCAD has a movable user coordinate system
3. It can set viewpoints from any location in space that can look in any directions
4. The computer screen can be divided into multiple viewports for simultaneously viewing 3D space from different viewpoints and different direction

18. 5. AutoCAD has a good assortment of surface entities for making surface models that have a variety of shapes
6. Solid models of most objects typically manufactured in machine shop can be made within AutoCAD
7. 3D models can be transformed into standard multi-view, dimensioned production drawing
8. AutoCAD has a built-in renderer with lights and surface materials, capable of making realistic-looking shaded picture from 3D models

19. The end…