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5 May 2004 Automatic calibration of an optical see-through head-mounted display for augmented reality applications in computer-assisted interventions
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Abstract
We are developing an optical see through head mounted display in which preoperative planning data provided by a computer aided surgery system is overlaid to the optical image of the patient. In order to cope with head movements of the surgeon the device has to be calibrated for a wide zoom and focus range. For such a calibration accurate and robust localization of a huge amount of calibration points is of utmost importance. Because of the negligible radial distortion of the optics in our device, we were able to use projective invariants for stable detection of the calibration fiducials on a planar grid. The pattern at the planar grid was designed using a different cross ratio for four consecutive points in x respectively y direction. For automated image processing we put a CCD camera behind the eye piece of the device. The resulting image was thresholded and segmented, after deleting the artefacts a Sobel edge detector was applied and the image was Hough transformed to detect the x and y axes. Then the world coordinates of fiducial points on the grid could be detected. A series of six camera calibrations with two zoom settings was done. The mean values of the errors for the two calibrations were 0.08 mm respectively 0.3 mm.
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Michael Figl, Christopher Ede, Wolfgang Birkfellner, Johann Hummel, Rudolf Seemann, and Helmar Bergmann "Automatic calibration of an optical see-through head-mounted display for augmented reality applications in computer-assisted interventions", Proc. SPIE 5367, Medical Imaging 2004: Visualization, Image-Guided Procedures, and Display, (5 May 2004); doi: 10.1117/12.534020; https://doi.org/10.1117/12.534020
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