Lecture 4 Friday 21 April 2023 1

ENGINEERING GRAPHICS1E7

Lecture 4: Orthographic Projections 2

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Projections (1)• Projections transform points from n

(here, n = 3) dimensional space into a space of dimension less than n (here, n = 2)

• Points to be considered,– Location of object

– Location of observer

– Plane of projection

– Projectors

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Projections (2)Projections

Parallel/Cylindrical

Perspective/Conical

Oblique Orthographic One-Point Three-PointTwo-Point

Cabinet

Other

Cavalier

Multi-view

Axonometric

First-angle Fourth-angle Third-angle Second-angle

Isometric (30°)

Di-metric Trimetric

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Parallel Projections

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Perspective Projections

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Oblique Projections

• Projectors are parallel to each other but not perpendicular to projection plane

•  An oblique projection shows front and top surfaces that include the three dimensions of height,  width,  and  depth.  

• The  front  or  principal  surface  of an  object  (the surface toward the plane of projection) is parallel to the plane of projection.

• Effective in pictorially representing objects

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Orthographic Projections

• Orthographic  projections  are   drawings  where  the  projectors, the observer or station point remain parallel to each other and perpendicular to the plane of projection.

• Orthographic  projections  are   further  subdivided  into  axonometric projections and multi-view projections.

• Effective in technical representation of objects

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Axonometric

• The observer is at infinity & the projectors are parallel to each other and perpendicular to the plane of projection. #

• A key feature of axonometric projections is that the object is inclined toward the plane of projection showing all three surfaces in one view.   

• The length of the lines, sizes of the angles, and proportions of the object varies according to the amount of angle between the object and the plane of projection. 

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First Angle Projection

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First Angle Projection 1

How to draw plan and elevation?

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First Angle Projection 2

How to draw end view?

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First Angle Projection 3

Points to remember:

• The ‘front view’ (or elevation) is the view with maximum information.

•The ‘plan’ is below the ‘elevation’ (in projection).

•The ‘end view’ is placed on the right if viewed from left side of object and on the left if viewed from right side.

•‘End view’ and plan face inwards from ‘elevation’.

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Third Angle Projection

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Third Angle Projection 1

How to draw plan and elevation?

In 3rd angle projection planes are transparent and objects are viewed through them

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Third Angle Projection 2

How to draw end view?

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Third Angle Projection 3

Points to remember:

• The ‘front view’ (or elevation) is the view with maximum information.

•The ‘plan’ is above the ‘elevation’ (in projection).

•The ‘end view’ is placed on the right if viewed from right side of object and on the left if viewed from left side.

•‘End view’ and plan face outwards from ‘elevation’.

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Example 1

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Example 2

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Example1 movie

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Example 2 movie