Roll Angle in 6DOF Tracking

Abstract

In a 3-D polar measurement system which tracks a probing device in six degrees of freedom (6DOF), the probe’s roll angle can be identified as a critical parameter in some system design concepts. This paper reviews methods and proposals for roll angle measurement in single laser tracker systems based on existing implementations and published concepts. a touch probe or the laser spot on a noncontact probe or scanner, the probe must be tracked in 6DOF to calculate the offset vector from tracked to measured point. Standard single laser tracking measures the 3-D location of a target retroreflector by range and two angles (approximately horizontal and vertical). The three angular elements of the target, here identified as roll, pitch, and yaw angles (see figure 1), can be measured as a combined result from single image processing. Two methods are well-represented here: • Leica’s T-System uses a zoom camera image of targets on the probing device which surround the reflector. The technique is essentially a photogrammetrist’s space resection in which the range data is discarded. See Loser and Kyle, 2003. • Past research at the Technical University of Vienna (no longer active) projected the return beam onto a CCD chip. The angular orientation could be determined from the shadow image of the reflector edges. See Prenninger et al., 1993.