1. A manipulator incorporating a system for determining relative positions of arm segments of its manipulator arm comprising a manipulator having a base pivoted for rotational movement around a first axis, a manipulator arm having a first and a second arm segment, said first arm segment pivotally mounted on said base about a second axis and said second arm segment pivotally connected to said first arm segment about a third axis located adjacent an end of sid first arm segment remote from said second axis, said second and third axes being substantially parallel and substantially perpendicular to said first axis, camera means mounted on said base in fixed relation to said first and second axes and including in its field of view said first and second arm segments in substantially all their positions of movement, said camera means acquiring representations of each of said first and second arm segments to provide image data, computer means receiving said image data, said computer means extracting image features from said data representative of said first and second arm segments, said computer means including an articulated model of said manipulator arm in its various positions and comparing said image data with said model to determine the relative positions of said arm segments, wherein said computer means generates an arm segment map of the location of said first and second arm segments and said extraction of image data includes determining edge points in said image, said computer comparing said edge points with said arm segment map and retaining only those edge points likely to form an edge on said arm segment map.