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