3D Time-of-flight distance measurement with custom - Universität ...

OPTICAL TOF RANGE MEASUREMENT 11
2.1 Overview of range measurement techniques
2.1.1 Triangulation
This ranging technique has been known and used by nature for millions of years. It
is, in the form of stereo-vision together with the depth-of-focus system (which so to
speak also belongs to triangulation systems), the basis for human depth perception.
Triangulation is a geometrical approach, where the target is one point of a triangle
whose two remaining points are known parts of the measurement system. The
distance of the target can then be determined by measuring the triangle’s angles or
the triangulation base. Literature distinguishes passive and active triangulation
techniques. Both principles are illustrated in Figure 2.2.
Figure 2.2 Principles of passive (left) and active (right) triangulation rangefinding.
Passive techniques rely on observing the same point from two different sites A and
B of known distance x and measuring the viewing angles α and β with respect to
the base AB. The observed point’s distance z can then be calculated using the
following equation:
x
z =
1
+
tan α
1
tan
β
Equation 2.1
Since each point to measure must be identified from both viewing positions
unambiguously, passive triangulation techniques require a scene with high contrast.
Stereovision is one famous 3D realization of passive triangulation [MAZ]. This
technique uses at least two cameras to observe the scene from different angles.