Proxima ASA STH-MD1/-C User Manual
Page 9
STH-MD1 U
SER
’
S
M
ANUAL
?
2001 V
IDERE
D
ESIGN
9
chooses the focal length based on the narrowest field of view acceptable for
an application, and then takes whatever range resolution comes with it.
4.6 Range Resolution
Range resolution is the minimum distance the stereo system can
distinguish. Since stereo is a triangulation operation, the range resolution
gets worse with increasing distance from the stereo head. The relationship
is:
d
bf
r
r
?
?
?
2
,
where b is the baseline between the imagers, f is the focal length of the
lens, and
d
?
is the smallest disparity the stereo system can detect. For the
STH-MD1/-C, b is 90 mm, and
d
?
is 0.46875 um (pixel size of 7.5 um,
divided by the interpolation factor of 16).
Figure 4-1 plots this relationship for several focal lengths. At any distance,
the range resolution is inversely proportional to the focal length.
4.7 Field of View
The field of view is completely determined by the focal length. The
formulas for the FOV in horizontal and vertical directions are:
)
/
8
.
4
arctan(
2
f
HFOV
?
)
/
8
.
3
arctan(
2
f
VFOV
?
where f is in millimeters. For example, a 4.8 mm lens yields a horizontal
FOV of 90 degrees. This is about the smallest practical focal length for the
STH-MD1.
The following table shows the FOV for some standard focal lengths.
Figure 4-1 Range resolution in mm as a function of distance, for
several different lens focal lengths.
Lens focal length
Horizontal FOV
Vertical FOV
4.8 mm
90 deg
73 deg
8.5
57
44
12.5
50
38
16
22
17
Table 4-1 Horizontal and vertical field of view for
different lens focal lengths.