The document discusses multi-view orthographic projections used in technical drawing. It defines key terms like projection, view, and orthographic projections. It explains the different reference planes used - horizontal plane, vertical frontal plane, and profile plane. It also discusses the different views - front view, top view, and side view. It describes the first angle and third angle projection systems and methods. It explains how to project views of points, lines, planes and solids by using the different reference planes and projection lines.

1. Lecture 6 (06.08.12):
Theory of Multi-view Orthographic
Projections
Dr. Sharad Gokhale
Civil Engineering Department, IIT Guwahati
208, M-Block, Academic Complex
Email: sharadbg@iitg.ernet.in
Telephone #: 2419

2. Multi-view Orthographic
PPrroojjeeccttiioonnss

3. Terms and definition
• Projection – image or the act of obtaining an
image of an object
• In technical drawing – we call it a view
• Method – we use projection mmeetthhoodd ttoo oobbttaaiinn
a view of an object

4. Orthographic Projections
• It is a technical drawing in which different views of
an object are projected on different reference
planes
• Different Reference planes (principal planes):
– HHoorriizzoonnttaall PPllaannee ((HHPP)),,
– Vertical Frontal Plane (VP)
– Side Or Profile Plane (PP)
• Different views:
– Front View (FV),
– Top View (TV),
– Side View (SV)

5. Projection System
Perspective

6. Projection System
Projection lines
Plane of Projections (POP)
Perspective
Parallel

7. Projection System
Projection lines
Plane of Projections (POP)
Perspective (Convergent
projection)
Parallel Projection
Three basic elements:
i. Object
ii. Observer
iii. POP

8. Projection ooff aann OObbjjeecctt
The outline on the plane of projection shows how the object appears to the
observer. In orthographic projection, projections from all points of the
object extend parallel to each other and perpendicular to the plane of
projection.

9. X
Y

10. X
Y
VP
1st 2nd Quad. Quad.
X Y
Observer
HP
3rd Quad. 4th Quad.
This quadrant pattern,
If observed along x-y line ( in red arrow direction) will exactly appear as shown on
right side and hence, It is further used to understand illustration properly.

11. Methods of Drawing Orthographic Projections
First Angle Projections Method
Here views are drawn
by placing object
in 1st Quadrant
Third Angle Projections Method
Here views are drawn
by placing object
in 3rd Quadrant.
( FV above X-Y, TV below X-Y )
( TV above X-Y, FV below X-Y )
FV
TV
X Y X Y
TV
FV
G L
Symbolic presentation of both methods
with an object standing on HP (ground) on it’s base.
NOTE:-
HP term is used in 1st angle method
&
ground term is used
in 3rd angle method of projections

12. Planes
PRINCIPAL PLANES
HP AND VP
Profile Plane (P.P.)
AUXILIARY PLANES
Auxiliary Vertical Plane
(A.V.P.)
A.V.P.
^ to HP & Ð to VP
Auxiliary Inclined Plane
(A.I.P.)

13. Planes & Views (first angle method)
This is a pictorial set-up of all three planes. Arrow direction is a
normal way of observing the object. But in this direction only VP and a
view on it (FV) can be seen. The other planes and views on those can
not be seen.
Procedure to solve above problem:-
To make those planes also visible from the arrow direction,
i) HP is rotated 900 downward, ii) PP, 900 in right side direction.
This way both planes are brought in the same plane containing VP.
HP IS ROTATED DOWNWARD 900
AND
BROUGHT IN THE PLANE OF VP.
X
Y
PP IS ROTATED AWAY IN RIGHT SIDE 900
AND
BROUGHT IN THE PLANE OF VP.
VP
LSV
X Y
HP
PP
FV
TV
ACTUAL PATTERN OF PLANES & VIEWS
OF ORTHOGRAPHIC PROJECTIONS
DRAWN IN
FIRST ANGLE METHOD OF PROJECTIONS

14. FOR T.V.
First angle projection
IN THIS METHOD,
THE OBJECT IS ASSUMED TO BE
SITUATED IN FIRST QUADRANT
MEANS
ABOVE HP & INFRONT OF VP.
OBJECT IS INBETWEEN
OBSERVER & PLANE.
PP
VP
FV LSV
X Y
HP
TV
ACTUAL PATTERN OF
PLANES & VIEWS
IN
FIRST ANGLE METHOD
OF PROJECTIONS

15. FOR T.V.
THIRD ANGLE
PROJECTION
IN THIS METHOD,
THE OBJECT IS ASSUMED TO BE
SITUATED IN THIRD QUADRANT
( BELOW HP & BEHIND OF VP. )
PLANES BEING TRANSPERENT
AND INBETWEEN
OBSERVER & OBJECT.
TV
X Y
LSV FV
ACTUAL PATTERN OF
PLANES & VIEWS
OF
THIRD ANGLE PROJECTIONS

16. Orthographic projections
- points, lines, planes, and solids
• To draw projections of any object, one must
have the following information
– Object (with it’s description, well defined)
– Observer (always observing perpendicular to respective
rreeffeerreennccee ppllaannee))
– location of object (means it’s position with reference to
HP & VP)
• Terms ‘above’ & ‘below’ with respective to HP and terms
‘infront’ & ‘behind’ with respective to VP form 4 quadrants.
• Objects can be placed in any one of these 4 quadrants

17. UNDERSTANDING PPRROOJJEECCTTIIOONNSS
To make and interpret drawings you need to know how to
create projections and understand the standard arrangement of
views.
You need to be familiar with the geometry of objects and
be able to visualize a 3D object that is represented in a
2D drawing.

18. VViieewwss ooff OObbjjeeccttss
The system of views is called
multi-view projection. Each
view provides certain definite
information. e.g. a front view
shows the true shape and size
of surfaces that are parallel to
the front of the object.

19. PPrriinncciippaall DDiimmeennssiioonnss
The three principal dimensions of an object are width,
height, and depth.
The front view shows only the height and
width of the object and not the depth.
In fact, any principal view of a 3D object
shows only two of the three
principal dimensions; the third is found
in an adjacent view.
Height is shown in the rear, left-side,
front, and right-side views.
Width is shown in the rear, top, front, and
bottom views.
Depth is shown in the left-side, top, right-side,
and bottom views.

20. Envision the object iinn aa GGllaassss BBooxx
To understand the standard arrangement of views on the sheet of paper

21. To draw the views on a sheet of paper, imagine the
six planes of the glass box being unfolded to lie flat.
Note the six standard
views (front, rear, top,
bottom, right side, left
side).

22. The GGllaassss BBooxx UUnnffoollddeedd
Lines extend around the glass box from one view to another on the planes of
projection. These are the projectors from a point in one view to the same point in
another view.

23. The Orthographic PPrroojjeeccttiioonn
The front, top, and right-side views of the object shown now without
the folding lines.

24. NNeecceessssaarryy VViieewwss
The top, front, and right-side views, arranged
together, are called the three regular views
because they are the views most frequently used.
A drawing should contain only the views needed to clearly and
completely describe the object.

25. View Selection
Select the most descriptive views
Use minimum number of views to
describe the object

27. How to project Side Views?
• Projecting across meter line
• Projecting through arcs
• Projecting through 45 degree projectors

28. Projecting across meter line
X1
FV
LHSV
45o
X Y
Y1
Meter line
TV

29. Projecting through 45o projectors
X1
FV
LHSV
X Y
Y1
45o projectors
TV

30. Projecting through arcs
X1
FV
LHSV
X Y
Y1
Arcs
TV

34. TopT vihewree basic views (FV, TV, SV) will provide
complete information about the real object
TToopp VViieeww

35. VVIIEEWWSS OOFF SSUURRFFAACCEESS
The three orientations that a plane surface can have to
the plane of projection are normal, inclined, and
oblique.
A plane surface that is
perpendicular to a plane of
projection appears on
edge as a straight line

36. Standard Views of Primitive Solids

37. Ex. 1 & 2: Draw the three
principal views of the
objects shown In fig 9.12
(a) and 9.13 (b)

38. Ex. 3 & 4: From the pictorial
view of the objects shown
In fig 9.14 (a) and 9.15 (b)
Draw FV, TV, RHSV