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4.1. USE CASES 21
(a) Tilting planar laser scanner. [9]
(b) Tf tree for a tilting
laser scanner.
Figure 4.3: Hardware setup and tf tree of a tilting laser scanner.
As it can be seen in Figure 4.3(b) the laser ranger is no longer mounted at a fix position on the
robot. It now changes its position due to the movement of the tilt unit. This use-case is even more
complex, because the captured laser scan no longer lies in the xy plane of the laser frame. It now lies
in a plane rotated about the x-axis. Figure 4.4 illustrates this two cases.
z
z
y
y
tilt axis
x
x
Figure 4.4: Tilting laser scanner moves the laser scan from the xy-plane to a oblique plane.
Main challenges in this use-case:
• Publish transformation continuously: The transformation has to be published continuously
to all interested components.
• Low latency: The transformation information should be delivered quickly to the interested
components, so that they can do their calculations.
• High synchronicity: In the case of the tilting laser scanner, the moment when the laser scan
and the pose of the tilt unit are captured, should be nearly the same. The amount of time
between the point when the laser scan and the point when the tilt unit pose is captured
influences the quality of the transformation.