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GLOBAL CALIBRATION FOR STEREO VISION PROBE

  • US 20080239327A1
  • Filed: 03/18/2008
  • Published: 10/02/2008
  • Est. Priority Date: 03/30/2007
  • Status: Active Grant
First Claim
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1. A method for calibrating a multi-view vision-based touch probe system, the method comprising:

  • (A) providing a manual touch probe comprising a marker pattern including at least three probe markers and a probe tip that is fixed relative to the marker pattern;

    (B) providing a multi-view triangulation system comprising at least two imaging viewpoints having intersecting fields of view, each viewpoint having a camera operable to provide an image of a probe marker located in the intersecting fields of view, and the triangulation system operable to determine first-level 3D coordinates for the probe marker based on a set of triangulation image comprising at least two respective images from at least two respective viewpoints;

    (C) providing a reference object at at least one imaging position in the intersecting fields of view, the reference object comprising a plurality of probe tip positioning reference features, wherein each of the plurality of probe tip positioning reference features has at least one of a known geometric relationship and a known coordinate relationship in relation to other probe tip positioning reference features;

    (D) providing a triangulation geometry characterization, that triangulation geometry characterization usable for determining 3D coordinates for a probe marker based on a set of triangulation images comprising at least two respective images of that probe marker from at least two respective viewpoints(E) estimating first-level 3D coordinates for each of a plurality of the probe tip positioning reference features positioned with the reference object at the at least one imaging position in the intersecting fields of view, the estimating comprising for each such probe tip positioning reference feature;

    (E1) constraining the probe tip against translation at that probe tip positioning reference feature, and providing at least four orientations of the manual touch probe and the marker pattern, and for each of those at least four orientations;

    (E1a) acquiring a corresponding set of triangulation images,(E1b) determining first-level 3D coordinates of at least 3 of the probe markers in the marker pattern for that orientation, including applying the provided triangulation geometry characterization, and(E1c) analyzing the first-level 3D coordinates of the at least 3 probe markers in the marker pattern to determine first-level 3D coordinates for a marker pattern reference point of the marker pattern for that orientation,(E2) estimating the first-level 3D coordinates for that probe tip positioning reference feature based on the first-level 3D coordinates of at least four marker pattern reference points corresponding to the at least four orientations, such that the first-level 3D coordinate position of the probe tip positioning reference feature is estimated to be approximately equidistant to each of the first-level 3D coordinate positions of the at least four marker pattern reference points;

    (F) determining a first-phase camera frame distortion characterization for at least one of errors and unknowns included in first-level 3D coordinates, based on comparing at least one of the known geometric relationships and the known coordinate relationships between the probe tip positioning reference features to corresponding relationships that are based on the estimated first-level 3D coordinates of the selected probe tip positioning reference features;

    (G) providing a final camera frame geometry calibration including a portion corresponding to the provided triangulation geometry characterization and a portion corresponding to a most-recent-phase camera frame distortion characterization comprising one of the first phase camera frame distortion characterization and a next-phase camera frame distortion characterization; and

    (H) providing a probe tip position calibration, comprising;

    (H1) for each of at least one probe tip positioning reference feature, and for each of at least four orientations of the touch probe at that reference feature, determining calibrated 3D coordinates for the marker pattern reference points corresponding to the marker pattern at that orientation and determining a calibrated Local Coordinate System (LCS) corresponding to the marker pattern at that orientation;

    (H2) for each of the at least one probe tip positioning reference features of step (H1);

    estimating its calibrated 3D coordinates based on the calibrated 3D coordinates of at least four marker pattern reference points corresponding to the at least four orientations of the touch probe at that probe tip positioning reference feature, such that the calibrated 3D coordinates of those at least four marker pattern reference points are approximately equidistant to the calibrated 3D coordinates of that probe tip positioning reference feature, andfor each of the at least four orientations of the touch probe at that probe tip positioning reference feature, determining a probe tip position vector that extends from the calibrated marker pattern reference point 3D coordinates expressed in the LCS corresponding to that orientation to the calibrated 3D coordinates of the reference feature expressed in the LCS corresponding to that orientation; and

    (H3) determining the provided probe tip position calibration based on the determined probe tip position vectors.

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