Engineering Graphics II
Projection Theory and
Multiview Drawings
Prof. Paul Kurowski
October 10, 2012
Projection Theory
Scheme for representing 3-dimensional
objects in a 2-dimensional medium (paper
or computer screen)
 Can represent all 3 dimensions in a single
image or use multiple views
 Working drawings are the practical result

Projection Theory

Based on two concepts:
 Line
of Sight
An imaginary ray of light between the observer’s
eye and the object
 Start at single point for perspective projections and
are parallel in parallel projections

 Plane

of Projection
An imaginary flat plane (paper, computer screen)
upon which the image created by the lines of sight
is projected
Perspective Projection
Parallel Projection
Projection Theory
Perspective projections mimic what the
eye sees, but are more difficult to
construct and do not show the true
dimensions of the object
 Parallel projections are most commonly
used in engineering graphics

Orthographic Projection


A parallel projection where the plane of projection is
perpendicular to the lines of sight
Can produce either pictorial drawings that show all three
dimensions at once, or multiview drawings that show
only two dimensions at a time
Multiview Drawings
Engineering drawings are used to
manufacture or construct whatever the
object is
 Pictorial drawings (perspective or
orthographic) distort dimensions and/or
angles, making fabrication difficult
 Multiview drawings show the true size and
shape of the two dimensions shown

Pictorial Distortion
Distorted dimensions and distorted angles
A Multiview Drawing by Albrecht Dürer
(1471-1528)
Multiview Projection

True size and shape
 Angles
are correct
 Circles are round
 Lengths are to scale
Multiview
Projection


Set of 2-D
views
representing
3-D object.
Views are
projections on
sides of ‘box’
containing
object.
Drawing formed by unfolding box
Drawing formed by unfolding box
Unfolding the glass box to produce a six view drawing
Most Common Views
Top (or Plan)
 Front View (or Elevation)
 Right Side View (or Profile)
 Cross sections show interior of object –
later!

Projection Angle
In Europe, First Angle Projection is used
 In North America, and in ES1050, Third
Angle Projection is used
 Be sure to select Third Angle Projection
for your drawings

First-Angle Projection (Europe)
Third-Angle Projection (North America)
Third-Angle Projection (North America)
Standard Practices




Choose front view as
most descriptive
Determine views to
best represent object
Use minimum number
of views to completely
describe object
Align views correctly
Line Conventions

Hidden Lines
 Some
features may not be visible in a given
view, but are still important.
 E.g. holes, surfaces, change of planes
 Hidden features are represented with a
dashed line
Hidden Lines
Line Conventions

Center Lines
 Used
to indicate the axes of symmetrical parts
and features (holes, cylinders, etc.)
 Consist of alternating long and short thin
dashes
Center Lines
Line Precedence

Visible lines have top priority

Hidden lines do not cross or have priority
over visible lines

Centre lines do not cross or have priority
over visible or hidden lines
How to Create 3-View Drawings
Block in front, top and right side views
using the overall width, height and depth.
 Sketch the front.
 Using construction lines project to top and
right.
 Block in major features seen in each view

How to Create 3-View Drawings
How to Create 3-View Drawings
How to Create 3-View Drawings
Draw Multiview
E-drawing solution
Draw Multiview
Draw Multiview
Draw Multiview
Draw Multiview
Draw Multiview
Draw Multiview
Draw Multiview