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MODULE 5
ORTHOGRAPHIC PROJECTION
AutoCAD 2D-1
ORTHOGRAPHIC PROJECTION
Module Objectives
Identify surfaces in two-dimensional views from a given three
dimensional views.
Demonstrate an understanding of the glass box method.
Correctly sketch two-dimensional views from a given three
dimensional view.
Differentiate between first and third angle projection in standard
terms.
Produce detailed drawings in third angle projection from a
given isometric drawing.
ORTHOGRAPHIC PROJECTION
1. Introduction
• An orthographic projection is a
2-dimensional representation of a 3-
dimensional object.
• It is a system of drawing views of an
object using perpendicular projectors
from the object to a plane of projection
See Fig.5.1.
Fig.5.1: Orthographic projection
ORTHOGRAPHIC PROJECTION
2. Principle Views
• Any object can be viewed from six
perpendicular views as shown in Fig. 5.2.
• It is clear that there are two main planes
used in orthographic projection, one is the
horizontal plane and the other is the vertical
plane.
• These planes intersect and divide space
into four quadrants. See Fig.5.3.
Fig.5.2:The six principle views
Fig. 5.3: Quadrant Pattern
ORTHOGRAPHIC PROJECTION
3. The glass box method
• One way to understand the
standard arrangement of views on a
sheet of paper is to envision the
object in a glass box.
• The outside observer would see
six standard views of the object
through the sides of this
imaginary glass box as shown in
Fig.5.4. Fig. 5.4: The glass box method
ORTHOGRAPHIC PROJECTION
3.1 The glass box procedure
• The object is placed in a
glass box.
• The image of the object is
projected on the sides of the
box.
• The box is unfolded as shown
in Fig.5.5.
• The sides of the box are the
principle views.
ORTHOGRAPHIC PROJECTION 4 First and Third Angle Projection
• As explained in the glass box method
mentioned above, when the box is unfolded
six views will eventually appear.
• There are 3 completely different views out of
the 5 views and the other 3 are repeated from
different angle of projection, this will take us
to the two main forms of angle projection.
The first angle and third-angle projection:
• In the third angle each view is placed at the
same direction relative to the front view,
while in first-angle the places are reversed.
Fig 5.6 shows the symbols of the first and third
angle projection.
Fig. 5.6. projection symbol
Fig. 5.7:First and Third angle Projection
ORTHOGRAPHIC PROJECTION
• The first angle projection is used in Europe while the third angle projection
is used in the united states.
• An example of the first and third angle projections are shown in Fig. 5.7 and5.8.
Fig. 5.7:First and Third angle Projection
Fig. 5.8:Multi-views in the third angle
projection
ORTHOGRAPHIC PROJECTION
4.1 Examples of multi-view drawings in third angle projection
• Study each picture and the accompanying orthographic views and note the
projection of all features.
CLASS ACTIVITY 1
• Using the third angle projection, draw the top, front and side views of
the isometric drawing shown below
CLASS ACTIVITY 2
• Using the third angle projection, draw the following orthographic
views of the isometric drawing shown below.
Front view.
Side view.
Top view.
HOMEWORK 4 - AT THE
BACK OF MODULE 4
Due next class
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