M Jawad Qarni, FME, GIK Institute 1

ME-102 Engineering ME-102 Engineering GraphicsGraphicsIntroduction to ProjectionsLecture # 2 & 3

By: Muhammad Jawad QarniResearch Associate

Faculty of Mechanical EngineeringGhulam Ishaq Khan Institute of Engineering Sciences & Technology

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Projections and Projectors

Projectors or LOSThe rays of light reflecting from different edges of the object, are known as projectors.

ProjectionsThe image formed on the plane as a result of projectors is known as projection.

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Projectors

Projections

Projections and Projectors

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Projection Theory

Engineering and technical graphics are dependent on projection methods.

There are two projection methodsPerspectiveParallel

Projection theory comprises the principles used to graphically represent 3D object and structures on 2D media

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Projection Theory

Isometric Views

(3D)

Orthogonal Views (2D)

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Projection Theory

Based on two variablesLine of Sight (LOS) is an imaginary ray of

light between an observer’s eye and an object.

Plane of Projection (i.e. an image or picture plane) is an imaginary flat plane upon which the image created by the lines of sight is projected.

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LOS & Plane of Projection

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Projection Methods

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Projection Methods

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Perspective Projection

Perspective projection mimic what the human eye sees.

Requires that the object be positioned at finite distance and viewed from a single point (SP: Station Point)

Projectors are not parallel. Image formed is always shorter than the

actual dimension of the object.Are somewhat difficult to create.

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Perspective View

Distorted dimensions

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Perspective view

Observer

Short Image

Object

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Perspective View (Illustration)

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Perspective drawings

VP

VP

VP

VP

VPVP

VP = Vanishing Point

Are classified by the number of vanishing points

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Parallel Projections

If the distance from the observer to the object is infinite, then the projectors (i.e. projection lines) are parallel.

Requires that the object be placed at infinity and viewed from multiple points on an imaginary line parallel to the object.

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Parallel Projections

Projectors

Projections

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Parallel Projection (Illustration)

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Orthographic ProjectionsParallel projection technique.Plane of projection is placed b/w the

observer and the object.Plane of projection is perpendicular to the

parallel lines of sight.Face of object is parallel to the plane of

projection.Final projection formed is of true size.

Can produce either pictorial drawing (3D) or multi-view (2D) in one view.

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Orthographic projection (Illustration)

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Multiview (Orthographic Projection)The object is oriented such that only two of its dimensions are shown.

The features of the part are outlined.

Generally three views of an object are drawn.

Features and dimensions in each view accurately represent the actual object.

Each view is a 2D flat view.

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Multiview (Orthographic Projection)

Profile Plane HorizontalPlane

Object

Frontal Plane

Projectors

Projection

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Frontal Plane of Projection:

The front view of an object shows the width and height dimensions.

Horizontal Plane of Projection:

The top view of an object shows the width and depth dimensions.

Profile Plane of Projection:

The side view of an object shows the depth and height dimensions.

Multiview Drawings

???

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Multiview Drawings

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Multiview Drawings

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Glass Box Example

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Unfolding Glass Box

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Six Principal Views

Mutually perpendicular views produced by mutually perpendicular planes of projection.

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Animation…

Animation of Glass Box

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View SelectionDetermine the best position of the object.Define the front view.Determine the minimum number of views

needed to completely describe the object so that it can be produced.

Once the front view is selected, determine which other views will have the fewest number of hidden lines.

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Orientation

Bad

Most of the lines are parallel and perpendicular to the views

Good

Many hidden lines

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View Selection

Natural position for front view Minimum number of views

Most descriptive view

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Axonometric Projection Is a parallel projection technique used to create a

pictorial drawing of an object by rotating the object on an axis relative to a projection or picture plane.

LOS are perpendicular to the plane of projection, therefore orthographic.

Display three dimensions.

Classification: Isometric Dimetric Trimetric

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Isometric View

If all the three faces of the object are at same angle with respect to the plane, the view obtained is called the isometric projection.

Most easy to draw.

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Isometric View

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Dimetric View

Two out of three faces of the object, makes same angle with respect to the plane.

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Trimetric View

All the faces of the object, that are inclined to the plane are at different angles relatively.

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Oblique Projection Is the basis for oblique drawing and

sketching.Form of parallel projection, projectors are

parallel to each other.Projectors are not perpendicular to the plane

of projection.One face of an object is parallel to the plane

of projection.

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Oblique projection• The object face is parallel to the frontal plane.

• This face will be drawn true size and shape.

• This face should include complex features (arcs, holes, irregular surfaces)

• The longest dimension should be parallel to frontal plane.

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Summary, Projection techniqueA. Multiview.

B. Axonometric

C. Oblique

D. Perspective

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Auxiliary Views

An Auxiliary view is an orthographic view that is projected onto any plane other than one of the six principal plane.

Sometimes one of the six principal views will not completely describe an object.

When there are inclined or oblique planes or features on an object.

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Auxiliary Views

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Auxiliary view (Illustration)

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Some practice problems…

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Thank you…