Computer Aided Engineering Design

50 COMPUTER AIDED ENGINEERING DESIGN

Figure 2.21 Perspective projection of P on the x-y plane

Figure 2.20 Classification of projections using a cube

Projections

Parallel projections

Oblique projections Orthographic

projections

Axonometric

projections (isometric,

dimetric and trimetric)

Multiple view

projections (first

and third angle

projections)

b

a c

∠a = ∠b = ∠c,

isometric

b

c

a

∠a = ∠b≠∠c,

dimetric

∠a≠∠b≠∠c,

trimetric

c

a

b

Full depth

cavalier

Half depth

cabinet

Variable depth

general

Three point

Two point

One point

Linear perspectives Aerial perspectives

Perspective projections

Thus, |EP| = | |, or P P EP = P P

w

z

w

z

⎛

⎝

⎞

⎠

⎛

⎝

⎞

⎠

since both vectors are colinear. From vector geometry, we get

z P

O

B

A

y

P′

P*

E

C

D

x