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Method of calibration of imaging devices

  • US 5,550,376 A
  • Filed: 05/22/1995
  • Issued: 08/27/1996
  • Est. Priority Date: 05/22/1995
  • Status: Expired due to Fees
First Claim
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1. A method of comparing points on a CAD model of a part and markers located at known CAD coordinates, to points on a physical part having several high-accuracy surface points, created from the CAD model comprising the steps of:

  • a) fixing the physical part to a fixture having a set of physical markers with locations relative to each other being the same as the relative locations CAD markers;

    b) adjusting the location of the physical part such that the relation between the high accuracy surface points and the physical markers is the same as the corresponding location of the high accuracy points of the CAD part to the CAD markers;

    c) acquiring linear pushbroom (LPB) projection images of said physical part with an imaging device at several preselected angles about an axis of rotation passing through the center of the physical part;

    d) selecting a projection image;

    e) identifying 2D screen coordinates (uij,vij) for the centers of each physical marker i for the jth projection image and the corresponding 3D known CAD coordinate, (xi,yi,zi);

    f) iteratively determining a global rotation calibration matrix G which defines a solid body rotation from a CAD coordinate system fixed with respect to the CAD model, to a coordinate system fixed with respect to the imaging device, and a projection matrix Mj for mapping 3D coordinates fixed with respect to the imager coordinate system to 2D screen coordinates of the projection image according to;

    
    
    space="preserve" listing-type="equation">(u.sub.ij,v.sub.ij)=M.sub.j ·



    (x.sub.i,y.sub.i,z.sub.i);

    g) repeating steps "d"-"f" for a plurality of other projection images, starting with a previous value of G to determine other projection matrices Mj and to refine the value of G; and

    h) employing the equation of step "f" with the matrices Mj, G, to map between CAD model coordinates and screen locations of the projection images.

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