Graphics Reference
In-Depth Information
1.3 Static 3D Face Modeling
1.3.1 Laser-stripe Scanning
Laser-stripe triangulation uses the well-known optical triangulation described in section 1.2.
A laser line is swept across the object where a CCD array camera captures the reflected light,
its shape gives the depth information. More formally, as illustrated in Figure 1.3, a slit laser
beam, generated by a light projecting optical system, is projected on the object to be measured,
and its reflected light is received by a CCD camera for triangulation. Then, 3D distance data
for one line of slit light are obtained. By scanning slit light with a
galvanic mirror
, 3D data
for the entire object to be measured are obtained. By measuring the angle 2
, formed by
the baseline
d
(distance between the light-receiving optical system and the light-projecting
optical system) and by a laser beam to be projected, one can determine the
z
-coordinate
by triangulation. The angle
π
−
θ
is determined by an instruction value of the galvanic mirror.
Absolute coordinates for laser beam position on the surface of the object, denoted by
p
,are
obtained from congruence conditions of triangles, by
θ
−
.
θ
z
f
0
=
d
z
tan(
)
.
(1.7)
p
This gives the
z
-coordinate, by
df
0
=
)
.
z
(1.8)
p
+
f
0
tan(
θ
Solve question 1 in section 5.5.3 for the proof.
Laser source
Laser be
am
Mirror
(deflector
)
Θ
baseline : d
Range point
z?
f
P
Optical axis
p
Surface to
be measured
Imaging lens
CCD sensor
Position
in CCD
Figure 1.3
Optical triangulation geometry for a laser-stripe based scanner