1. TA 101: Technical Arts 2015-16 II Dr. Prishati Raychowdhury
Department of Civil Engineering
IIT Kanpur
Office: FB 336; Phone: 6692

2. Orthographic Projections
Lecture 4
Orthographic Projections

3. Orthographic Projections: Review
Orthographic projection is a 2D representation of a 3D object
The projecting rays are perpendicular to the plane of projection
The rays forming an image on the plane of projection are parallel to each other
The observer is at infinity
Principal views are obtained using three mutually perpendicular projection planes

4. Three important things about any projection:
OBJECT, OBSERVER, PLANE of PROJECTION
Case 1: OBJECT PLANE of PROJECTION OBSERVER
Case 2: OBSERVER OBJECT PLANE of PROJECTION
Case 1: Third Angle Projection Method
Case 2: First Angle Projection Method

5. Third Angle Projection
Projection plane is between object and observer (i.e., object is inside the glass box)

6. Top view
Front view
Side/Profile view

7. Third Angle Projection
Top view
Front view
Right side view

8. First Angle Projection
Object is between the observer and projecting plane (i.e., object is outside the glass box)

9. First Angle Projection

10. First Angle Projection
Right Side View
Front View
Top View

11. First and Third angle Projection
Front view
RHS view
Top view
Front View
RHS View
Top View
THIRD ANGLE PROJECTION
FIRST ANGLE PROJECTION

12. First and Third angle ProjectionII
III IV
I LV
I FV
I TV
III TV
III FV
Object in 1st quadrant : FIRST ANGLE PROJECTION
Object in 3rd quadrant : THIRD ANGLE PROJECTION

13. First/Third angle Top view
FIRST ANGLE PROJECTION
THIRD ANGLE PROJECTION

14. First/Third angle Front view
FIRST ANGLE PROJECTION
THIRD ANGLE PROJECTION

15. Projection Systems United States and Europe: 3rd angle projection
British Standards: 1st angle projection
India: Formerly only 1st angle projection was in use, now BIS standard allows both
In this course we will mainly use third angle projection system, unless mentioned otherwise
However, you should be able to read both

16. Convention to indicate THIRD Angle Projection
Symbol for THIRD Angle Projection System
LHS View
Front View

17. Convention to indicate FIRST Angle Projection
Symbol for FIRST Angle Projection System
Front View
LHS View

18. Symbols for 1st/3rd Angle Projection are generally present in the Title block

20. Example Third Angle Projection First Angle Projection RIGHT VIEW
FRONT VIEW
TOP VIEW
Third Angle Projection
First Angle Projection

21. Another Example Viewing faces Top Face Back Face Right Side Face
Left Face
Bottom Face
Front Face

22. Third Angle Projection
Object behind plane
Top View
Top
Front
Right
Front View
Right Side View

23. First Angle Projection
Object in front of plane
Right Side View
Front View
Back
Left
Bottom
Top View

24. Choosing right object orientation
Example: Guided ramp

28. Example 2

29. Example 2

30. Example 2

31. Example 2

32. Object Orientation The simplest position is to be used
Front view should get maximum details
Reduce the number of hidden lines
Principal faces are perpendicular to the sight directions (projection lines) and parallel to the projection planes

33. Selection of Views
Select the least number of views required which will completely explain the object
In some cases, one or two views are sufficient
In most cases, three views will be sufficient
For unsymmetrical objects, more than three views may be required

34. Spacing the Selected Views
Necessary to utilize the space efficiently
Do preliminary planning before actual drawing
Projecting the Views
Draw all the views concurrently
DO NOT attempt to complete one view before proceeding to another
You may require help from other views to complete a particular view

35. Order of Precedence of Lines
Firm Object Line
Hidden Object Line
Center Line
Projection Line/ Construction Line

36. Precedence of Lines

37. Hidden Lines Dashed Lighter than full lines Dashes of uniform length
No space
Join Dashes

38. Join dashes

39. Your Drawing Should Look Like This

40. Draw Views Concurrentlyα

41. Next Topic: Dimensioning
Thank you..
Next Topic: Dimensioning