This ppt will help students of Engineering Drawing to learn the concept of projection of point

1. Orthographic Projections
For drawing projections of any object a system is followed universally.
Two planes are considered :
Horizontal plane (H.P.)
Vertical Plane (V.P.)
The two planes are
1.Perpendicular to each other and their
intersection line is known as xy line.
2. Transparant
The planes divide the space in four quadrants
namely Ist, IInd,IIIrd and IVth quadrant
Ist Quadrant
II nd
Quadrant
III rd
Quadrant
IV th
Quadrant
If we see it from the front, it will be seen as X Y
V.P.
V.P.
F.V.
If we see it from the top, it will be seen as
T.V.
X Y
H.P.
H.P.

2. NOTATIONS
FOLLOWING NOTATIONS SHOULD BE FOLLOWED WHILE NAMEING
DIFFERENT VIEWS IN ORTHOGRAPHIC PROJECTIONS.
IT’S FRONT VIEW a’ 1’
OBJECT POINT A POINT 1
IT’S TOP VIEW a 1
IT’S SIDE VIEW a” 1”

3. FV & TV of a point always lie in the same vertical line
FV of a point ‘P’ is represented by p’. It shows position of the point with
respect to HP only. While drawing FV, XY line represents the HP and the
plane of paper represents the VP.
If the point P lies above HP, p’ lies above the XY line.
If the point P lies in the HP, p’ lies on the XY line.
If the point P lies below the HP, p’ lies below the XY line.
TV of a point ‘P’ is represented by p. It shows position of the point with
respect to VP only. While drawing TV, XY line represents the VP and the
plane of paper represents the HP.
If the point P lies in front of VP, p lies below the XY line.
If the point P lies in the VP, p lies on the XY line.
If the point P lies behind the VP, p lies above the XY line.
Basic concepts for drawing projection of point
FV does not give any information about position of the point w.r.t. VP
TV does not give any information about position of the point w.r.t. HP
X Y
p’
X Y
p’
X Y
p’
X Y
p
X Y
p
X Y
p

4. A point can have following nine positions
When a point A is 35 mm above the H.P. and 20mm in front of the V.P.
i.e. in first quadrant
CASE I
The point is in first Quadrant i.e. it is above the H.P. and in front of the V.P.
Ist
Quadrant
II nd
Quadrant
III rd
Quadrant
VI th
Quadrant
a
X Y
a’
35
20
8
Dimension should be placed
8 mm away from the
projectors

5. When a point B is 35 mm above the H.P. and 20mm behind the V.P. i.e.
in second quadrant
X
Y
Ist
Quadrant
II nd
Quadrant
III rd
Quadrant
VI th
Quadrant
b
X Y
b’
35
20
CASE II
The point is in second Quadrant i.e. it is above the H.P. and behind the V.P.

6. When a point C is 35 mm below the H.P. and 20mm behind the V.P. i.e.
in third quadrant
Ist
Quadrant
II nd
Quadrant
III rd
Quadrant
VI th
Quadrant
c
X Y
c’
35
20
CASE III
The point is in third Quadrant i.e. it is below the H.P. and behind the V.P.

7. When a point D is 35 mm below the H.P. and 20mm in front of the V.P.
i.e. in fourth quadrant
X
Y
Ist
Quadrant
II nd
Quadrant
III rd
Quadrant
VI th
Quadrant
d
X Y
d’
35
20
CASE IV
The point is in fourth Quadrant i.e. it is below the H.P. and in front of the V.P.

8. When a point E is in the H.P. and 30mm in front of the V.P. i.e. between
first and fourth quadrant
Ist
Quadrant
II nd
Quadrant
III rd
Quadrant
VI th
Quadrant
e
X Y
e’
30
CASE V
The point is in the H.P. and in front of the V.P. i.e. it is between first and fourth quadrant

9. When a point F is in the V.P. and 30mm above the H.P. i.e. between first
and second quadrant
CASE VI
The point is in the V.P. and above the H.P. i.e. it is between first and second quadrant
Ist
Quadrant
II nd
Quadrant
III rd
Quadrant
VI th
Quadrant
f
X Y
f’
30

10. When a point G is in the H.P. and 30mm behind the V.P. i.e. between
second and third quadrant
CASE VII
The point is in the H.P. and behind the V.P. i.e. it is between second and third quadrant
Ist
Quadrant
II nd
Quadrant
III rd
Quadrant
VI th
Quadrant
g
X Y
g’
30

11. When a point H is in the V.P. and 30mm below the H.P. i.e. between third
and fourth quadrant
CASE VIII
The point is in the V.P. and below the H.P. i.e. it is between third and fourth quadrant
Ist
Quadrant
II nd
Quadrant
III rd
Quadrant
VI th
Quadrant
h
X Y
h’
30

12. When a point J is in both H.P. and V.P.
CASE IX
Ist
Quadrant
II nd
Quadrant
III rd
Quadrant
VI th
Quadrant
j
X Y
j’

13. Draw Projection of following points on the same ground
line keeping the projectors 25 mm apart.
A: On the VP and 20 mm above the HP.
B: 30 mm below the HP and 40 mm behind the VP.
C: 50 mm above the HP and 25 mm behind the VP.
D: On the HP and 15mm in front of the VP.
E: 35mm above the HP and 50mm in front of the VP.
F:40 mm below the HP and on the VP.
G:35 mm behind the VP and on the HP.
H: 45 mm below the HP and 20mm in front of the VP.
J: on the HP and on the VP.

16. Problem: Projection of various points are given in the fig. State the position of each point with
respect to principal planes
30
10
30
10
45
35
20
45
45
15
30
20
X Y
a’
b’
c’
e’
f’
g’
d’
h’
a
b
h
g
c
d
e f