Part 01- Introduction to Orthographic Projections Introduction to Orthographic Projections (Theory) 2.1 Introduction to Projections-Principle Planes of Projection and Principle Views 2.2 Introduction to First angle, Second angle, Third angle and Fourth angle method with their symbolic representation. 2.3 Projection of points in All 4 Quadrants

1. Vidya Vikas Education Trust ®
Viday Vikas Polytechnic College
Department of Mechanical (General)
Mr. THANMAY J S Be, M-Tech, H.O.D Mechanical (General), Vidya Vikas Polytechnic College, Mysore Page 1
Computer Aided Engineering Drawing (20ME12P)
Unit – 02
Part 01- Introduction to Orthographic Projections
Introduction to Orthographic Projections (Theory)
2.1 Introduction to Projections-Principle Planes of Projection and Principle Views
2.2 Introduction to First angle, Second angle, Third angle and Fourth angle method with their
symbolic representation.
2.3 Projection of points in All 4 Quadrants

2. Vidya Vikas Education Trust ®
Viday Vikas Polytechnic College
Department of Mechanical (General)
Mr. THANMAY J S Be, M-Tech, H.O.D Mechanical (General), Vidya Vikas Polytechnic College, Mysore Page 2
2.1 Introduction to Orthographic Projections
An Orthographic projection is a 2-D representation of a 3-D object. The 2-D drawing represents
different sides of an object.
 This is such a type of drawing in which Parallel Projection is used for the preparation of
the drawing of an object.
 These lines are perpendicular to the plane.
 In this drawing, it is assumed that the object is at infinity.
 The shape of an object is seen in actual size in such drawing.
 A plane is an imaginary surface on which pictures are prepared imaginably. Then it is
transferred to the paper.
 This plane is faced toward the object whose view is to be prepared.
Generally, three views of an object are prepared. These are Top View, Front View, and Side
View.

3. Vidya Vikas Education Trust ®
Viday Vikas Polytechnic College
Department of Mechanical (General)
Mr. THANMAY J S Be, M-Tech, H.O.D Mechanical (General), Vidya Vikas Polytechnic College, Mysore Page 3
2.1.1 Principle Planes of Projection
A plane is an imaginary and invisible clear surface. The drawing constructed on this imaginary
curtain is transferred on the drawing sheet.
For example, if we look at some object through glass or plastic piece, then the picture of the
object will be seen there.
 This piece will work as a plane.
 However, this plane is not a material body.
 It is only an imaginary curtain, which is used to give the shape of a drawing by placing it
in different positions.
 This plane can be put in different positions.
 However, the plane placed in the following positions is called the Principal Plane.
Besides such positions, the plane will be called Auxiliary Plane.
1. Frontal Plane.
2. Profile Plane.
3. Horizontal Plane.

4. Vidya Vikas Education Trust ®
Viday Vikas Polytechnic College
Department of Mechanical (General)
Mr. THANMAY J S Be, M-Tech, H.O.D Mechanical (General), Vidya Vikas Polytechnic College, Mysore Page 4
1. Frontal Plane: Such a plane which is placed in front of an object, while projections are drawn,
is called the Frontal plane.
2. Profile Plane: Such a plane which is placed to the right or left of an object. Side view of the
object is drawn on this plane.
3. Horizontal Plane: This is a plane which is placed upward or downward in the horizontal
position of an object. Top view of the object is constructed on this plane.
2.1.2 Principle Views
The 6 principal views are created by looking at the object (straight on) in the directions
indicated. Following views are formed of an object in Orthographic Projection.
1. Front View.
2. Top View.
3. Back View.
4. Bottom View.
5. Right Side View.
6. Left Side View.

5. Vidya Vikas Education Trust ®
Viday Vikas Polytechnic College
Department of Mechanical (General)
Mr. THANMAY J S Be, M-Tech, H.O.D Mechanical (General), Vidya Vikas Polytechnic College, Mysore Page 5
2.2 Introduction to First angle, Second angle, Third angle and Fourth angle method with
their symbolic representation.
Rules of Orthographic Projections
1) Vertical and Horizontal Planes are
imaginary surface plane and transparent
which is intersected.
2) Object is Placed in any of the Four
Quadrant
3) View Direction is from right to left and top
to down in case of any quadrant.
4) The shape of an object is seen in actual size
in Planes of Projections (VP or HP).
5) Once the projections are drawn the original
object is taken out.
6) Vertical Plane (VP) is fixed and only
Horizontal plane is rotated clock wise till it
touches Vertical plane on other side, this
includes even rotation of Profile Plane in
line with Vertical Plane.
7) The symbolic representation is shown
along the drawing so that the engineers can
identify which quadrant it belongs to.
8) Vertical Plane annotations are represented
by („) ex a‟, b‟, c‟...etc.
9) Horizontal Plane annotations are
represented by ex a, b, c...etc.
10) Profile Plane annotations are represented
by (“) ex a”, b”, c”..etc.

6. Vidya Vikas Education Trust ®
Viday Vikas Polytechnic College
Department of Mechanical (General)
Mr. THANMAY J S Be, M-Tech, H.O.D Mechanical (General), Vidya Vikas Polytechnic College, Mysore Page 6
Quadrant Orthographic 3D Plane of Projection after
Rotating HP
Symbolic Representation
of the Quadrant
First
Quadrant
or
First angle
of
Projection
Second
Quadrant
or
Second
angle of
Projection
Third
Quadrant
or
Third angle
of
Projection
Fourth
Quadrant
or
Fourth
angle of
Projection

7. Vidya Vikas Education Trust ®
Viday Vikas Polytechnic College
Department of Mechanical (General)
Mr. THANMAY J S Be, M-Tech, H.O.D Mechanical (General), Vidya Vikas Polytechnic College, Mysore Page 7
2.3 Projection of points in All 4 Quadrants
Representation terms used to explain the location of Points in any of the Four Quadrant
1) A Point (A)
15 mm above
HP and 20
mm in-front
of VP. Draw
its
Projections.

8. Vidya Vikas Education Trust ®
Viday Vikas Polytechnic College
Department of Mechanical (General)
Mr. THANMAY J S Be, M-Tech, H.O.D Mechanical (General), Vidya Vikas Polytechnic College, Mysore Page 8
2) A Point (B)
is 25 mm
above HP
and 30 mm
behind VP.
Draw its
Projections.
3) A Point (A)
is 15 mm
below HP
and 30 mm
behind of
VP. Draw its
Projections.
4) A Point (B)
is 35 mm
below HP
and 15 mm
In-front of
VP. Draw its
Projections.