Method and system for dynamically calibrating vehicular cameras

  • US 9,357,208 B2
  • Filed: 01/20/2012
  • Issued: 05/31/2016
  • Est. Priority Date: 04/25/2011
  • Status: Active Grant
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First Claim
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1. A method for dynamically ascertaining the position of a vehicular camera relative to a vehicle to which the camera is attached, the method comprising:

  • (a) establishing a plurality of vehicular steering angle ranges;

    (b) acquiring a set of image frames in a video stream provided by the camera whilst the vehicle is in motion, the image frames defining an image plane;

    (c) measuring the steering angle of the vehicle and, for each steering angle range;

    (i) selecting a plurality of feature points in the image frames;

    (ii) tracking a motion trajectory of each selected feature point in the set of image frames, and(iii) determining a vanishing point in the image plane for the plurality of tracked motion trajectories;

    (d) determining a vanishing line in the image plane provided by the camera based on a locus of said vanishing points;

    (e) determining the position or alignment of the camera based on the position of the vanishing line and the position of a central vanishing point, the central vanishing point being the vanishing point that is determined for the steering angle range that encompasses zero degrees;

    removing distortion in the motion trajectories caused by use of a wide angle camera lens;

    linearly fitting the undistorted motion trajectories to generate straight lines;

    wherein determining a vanishing point comprises determining the vanishing point in a given steering range by finding a substantial intersection point for the distortion free, straight line tracked motion trajectories in the given steering range;

    wherein the camera is a front facing camera and rotational angles α and

    β

    of the camera are determined as a function of d1 and d2, where;

    α

    is the rotation of the camera around an X-axis in a camera coordinate system,β

    is the rotation of the camera around a Y-axis in the camera coordinate system,d1 is a distance in the image plane from a principal point of the camera to a right angled projection point on the vanishing line, andd2 is a distance in the image plane along the vanishing line from the projection point to the central vanishing point; and

    wherein a rotational angle γ

    of the camera is determined by solving for γ

    as follows;


    A cos γ

    +B sin γ

    =C
    where,
    A−

    f sin α

    sin β


    B=f cos α


    C−

    (cvpX−

    axisX) sin α

    cos β

    where γ

    is the rotation angle around the Z-axis of a vehicle coordinate system, f is the focal length of the camera, cvpX is an image row coordinate of the central vanishing point in the image plane, and axisX is an image column location of the principal point.

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