Sequential updating of projective and affine structure from motion
We demonstrate how the affine coordinate frame can be periodically updated to prevent drift over time.Structure is recovered from image corners detected and matched automatically and reliably in image sequences.For rigid transformations, a unique metrical reconstruction is known to be possible from three orthographic views of four points.However, human observers seem able to obtain much shape information from a mere pair of views, as is evident in the case of binocular stereo.A structure from motion algorithm is described which recovers structure and camera position, modulo a projective ambiguity.Camera calibration is not required, and camera parameters such as focal length can be altered freely during motion.A mobile observer samples sequences of narrow-field projections of configurations in ambient space.
Thanks for helpful discussions with Richard Hartley, Jitendra Malik, John Mayhew, Joe Mundy, and to colleagues in the Robotics Research Group, particularly Andrew Blake, Mike Brady, Phil Mc Lauchlan, Ian Reid, Larry Shapiro, and Phil Torr.
We indicate how solutions of the structure-from-motion problem can be stratified in such a way that one explicitly knows at which stages various a priori assumptions enter and specific geometrical expertise is required.
An affine stage is identified at which only smooth deformation is assumed (thus no rigidity constraint is involved) and no metrical concepts are required.
Results are shown for reference objects and indoor environments.
Finally, the affine structure is used to construct free space maps enabling navigation through unstructured environments and avoidance of obstacles.