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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    International journal of computer vision 31 (1999), S. 83-98 
    ISSN: 1573-1405
    Keywords: time to collision ; rate of approach ; Green's theorem
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract The rate of approach (ROA) of a moving observer toward a scene point, as estimated at a given instant, is proportional to the component of the observer's instantaneous velocity in the direction of the point. In this paper we analyze the applicability of Green's theorem to ROA estimation. We derive a formula which relates three quantities: the average value of the ROA for a surface patch in the scene; a surface integral that depends on the surface slant of the patch; and the contour integral of the normal motion field around the image of the boundary of the patch. We analyze how much larger the ROA on the surface patch can be than the value of the contour integral, for given assumptions about the variability of the distance to points on the surface patch. We illustrate our analysis quantitatively using synthetic data, and we also validate it qualitatively on real image sequences.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    International journal of computer vision 13 (1994), S. 33-56 
    ISSN: 1573-1405
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract If an observer is moving rigidly with bounded rotation then normal flow measurements (i.e., the spatiotemporal derivatives of the image intensity function) give rise to a constraint on the oberver's translation. This novel constraint gives rise to a robust, qualitative solution to the problem of recovering the observer's heading direction, by providing an area where the Focus of Expansion lies. If the rotation of the observer is large then the solution area is large too, while small rotation causes the solution area to be small, thus giving rise to a robust solution. In the paper the relationship between the solution area and the rotation and translation vectors is studied and experimental results using synthetic and real calibrated image sequences are presented. This work demonstrates that the algorithm developed in (Horn and Weldon 1987) for the case of pure translation, if appropriately modified, results in a robust algorithm that works in the case of general rigid motion with bounded rotation. Subsequently, it has the potential to replace expensive accelerometers, inertial systems and inaccurate odometers in practical navigational systems for the problem of kinetic stabilization, which is a prerequisite for any other navigational ability.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    International journal of computer vision 15 (1995), S. 105-122 
    ISSN: 1573-1405
    Keywords: constraint intersection ; curvature and torsion ; dominant motion ; egomotion analysis ; Frenet-Serret motion model ; normal optical flow ; screw-motion equations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract In this paper we propose a new model,Frenet-Serret motion, for the motion of an observer in a stationary environment. This model relates the motion parameters of the observer to the curvature and torsion of the path along which the observer moves. Screw-motion equations for Frenet-Serret motion are derived and employed for geometrical analysis of the motion. Normal flow is used to derive constraints on the rotational and translational velocity of the observer and to compute egomotion by intersecting these constraints in the manner proposed in (Durić and Aloimonos 1991) The accuracy of egomotion estimation is analyzed for different combinations of observer motion and feature distance. We explain the advantages of controlling feature distance to analyze egomotion and derive the constraints on depth which make either rotation or translation dominant in the perceived normal flow field. The results of experiments on real image sequences are presented.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
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