3. 10. 1 ORTHOGONAL PROJECTION
A. Identify orthogonal projections
The orthogonal projection of an object
onto a plane is the image formed
on the plane by normals
from the object to the plane
4. A. Identify orthogonal projections
In the diagram 1, the
outline of the cuboid
as seen from above is
projected onto the
horizontal plane.
Thus, the rectangle
ABCD is the
orthogonal projection
of the cuboid onto the
horizontal plane.
DIAGRAM 1
A
B C
D
Object
Horizontal
plane
Orthogonal
projection
5. B. Drawing Orthogonal Projections
Step 1 :
From the corners of
the object, draw
normals to the plane
given
Step 2 :
Join up the feet of the
normals on the plane
to get the orthogonal
projection of the object
Object
Horizontal
plane
Orthogonal
projection
10. C Determining the difference between an object and its
orthogonal projection
A B
D C
P Q
RS
A/P B/Q
D/S C/R
The edges of an object and their
orthogonal projections onto a plane
are equal if the edges of the object
are parallel to that plane.
The edge, AB of the object is equal
to the edge of the orthogonal
projection of AB and, so on, since
the edges, AB, BC, an AD are
parallel to the horizontal plane.
11. C Determining the difference between an object and its
orthogonal projection
A B
D C
P Q
RS
A/P B/Q
D/S C/R
When viewed from above,
the corner, P, is beneath
the corner, A. Thus , the orthogonal
projection of this corner is labelled
as A/P. For similar reasons, the
orthogonal projection of corner B
is labelled as B/Q and so on.
12. D
C
E F
A B
D C
X
A/E B/F
C Determining the difference between an object and its
orthogonal projection
Edge AD of the object and the
orthogonal projection of AD onto
a plane are different in length,
since edge AD is not parallel to
the vertical plane.
Edge DE of the object and the
orthogonal projection of DE onto
a plane are equal in length,
since edge DE is parallel to
the vertical plane.
13. A Drawing the plan of a solid object
The orthogonal projection of an object
onto the horizontal plane is called
a plan
14. In drawing the plan of a solid object, the following
lines are used:
solid lines are used to show the visible edges
of the object
dashed lines are used to show the hidden edges
of the object
thin light lines, called projection lines, are used to
connect the plan and the elevations
21. B
Drawing the front and side elevations of a solid
object
The orthogonal projection of an object onto a the vertical
plane is called an elevation. The orthogonal projection of an
object, as seen from the front, onto the vertical plane, is
called the front elevation whereas, the orthogonal projection
of an object, as seen from the side, onto the vertical plane
is called the side elevation.
22. In drawing the elevation of a solid object,
the following lines are used:
solid lines are used to show the visible edges
of the object
dashed lines are used to show the hidden edges
of the object
thin light lines, called projection lines, are used to
connect the plan and the elevations
51. ORTHOGRAPHIC
PROJECTION
R
QP
N
M
N
Step 1: Relocate the width and
depth measurements of the entire
object. Draw surfaces M and N
Step 2: Project the top view of the
object onto the front view.
Relocate the height measurement
on the entire object. Then, draw
surfaces P and R
Step 3: Project the top and front
views on the object onto the right
side view. Draw the height and
depth of the entire object. Draw
surfaces N and Q
Solid With Inclined Surfaces
53. THIRD ANGLE PROJECTION
Top view
Left side view Front view
The three views when an object is projected
onto the vertical, horizontal and additional
vertical planes at third angle projections.
Example 2
54. Top view
Left side view
Front view
STEP 1
Construct projection line from top
view to left side view.
STEP 2
Construct projection line from front
view to left side view.
STEP 3
Draw the left side view.
Example 3
Question:
Construct a left side view of the
object shown above.
