Improving Haptic Exploration of Object Shape by Discovering Symmetries

The shapes of most real-world objects are symmetric with respect to at least one plane of symmetry. This information is unconsciously used by humans when they attempt to estimate the shape of an object in presence of uncertainty or missing evidence, for example if the object is partially occluded or if they are exploring the object by touch (i.e. haptic exploration). In robotics, this concept has been used for the visual estimation of object shape. However, no attempt has been made so far to incorporate this idea into hapticbased estimation. This work presents a method for the haptic exploration of object shape that includes the assumption that a symmetry could exist. The approach combines a tailored version of Gaussian Processes and a novel exploratory procedure that is able to detect the position and orientation of any plane of symmetry. Our results show that, if one or more symmetries exist, the object shape can be estimated faster and more accurately. Interestingly, in the case that no symmetry is present, the exploration process is only slightly slower, and the final accuracy of the shape estimation is not compromised.