Geoscience Reference
In-Depth Information
Fig. 4 Data measured using
terrestial laser scanner
3D point clouds
(XYZ) + intensity
value
Z
r
θ
X
Terrestrial laser
scanner
φ
Y
• Cartesian to spherical coordinates system.
Range
;
r ¼
p
x
2
þ
y
2
þ
z
2
x
y
Horizontal direction
;
u ¼ tan
1
ð
1
Þ
z
.
p
Vertical angle
;
h ¼ tan
1
x
2
þ
y
2
• Spherical to Cartesian coordinates system.
x ¼ r
sin
ð
u
Þ
cos
ð
h
Þ
y ¼ r
cos
ð
u
Þ
cos
ð
h
Þ
z ¼ r
sin
ð
h
Þ
ð
2
Þ
There are three types of beam deflection units used in TLS (1) Oscillating
mirrors (Fig.
5
a); (2) Rotating polygonal mirrors (Fig.
5
b); and (3) Monogon (flat)
rotating mirrors (Fig.
5
c) which represents the field of view (FOV) of the TLS.
According to Reshetyuk (
2009
), there are three classifications of TLS based on
FOV (1) camera scanner (Fig.
5
d); (2) hybrid scanner (Fig.
5
e); and (3) panoramic
scanner (Fig.
5
c).
Camera scanner uses oscillating mirrors to deflect the laser beam about the
horizontal and vertical axes of the scanner (Fig.
5
a). The scanning head remains
stationary during scanning process. It carries out the distance and angle mea-
surement over a much more limited angular range and within a specific
FOV (Fig.
5
d). Hybrid scanner has the horizontal FOV of 360 and limited vertical
FOV (Fig.
5
e). This scanner employs the oscillating or rotating polygonal mirrors
(Fig.
5
b) to deflect the laser beam in vertical and horizontal axes. With aid of
servomotor, hybrid scanner is capable of rotating by a small step around the
vertical axis (horizontally). It works by scanning the vertical profile using the
mirror, and this step is repeated around the vertical axis until the scanner rotates
for 360. Monogon mirror (Fig.
5
c) used in panoramic scanner has improved the
