21 June 2015 Determining the coordinates of lamps in an illumination dome
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The UCL Dome consists of an acrylic hemisphere of nominal diameter 1030 mm, fitted with 64 flash lights, arranged in three tiers of 16, one tier of 12, and one tier of 4 lights at approximately equal intervals. A Nikon D200 digital camera is mounted on a rigid steel frame at the ‘north pole’ of the dome pointing vertically downwards with its optical axis normal to the horizontal baseboard in the ‘equatorial’ plane. It is used to capture sets of images in pixel register for visualisation and surface reconstruction. Three techniques were employed for the geometric calibration of flash light positions in the dome: (1) the shadow cast by a vertical pin onto graph paper; (2) multi-image photogrammetry with retro-reflective targets; and (3) multi-image photogrammetry using the flash lights themselves as targets. The precision of the coordinates obtained by the three techniques was analysed, and it was found that although photogrammetric methods could locate individual targets to an accuracy of 20 μm, the uncertainty of locating the centroids of the flash lights was approximately 1.5 mm. This result was considered satisfactory for the purposes of using the dome for photometric imaging, and in particular for the visualisation of object surfaces by the polynomial texture mapping (PTM) technique.
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Lindsay W. MacDonald, Lindsay W. MacDonald, Ali Hosseininaveh Ahmadabadian, Ali Hosseininaveh Ahmadabadian, Stuart Robson, Stuart Robson, "Determining the coordinates of lamps in an illumination dome", Proc. SPIE 9528, Videometrics, Range Imaging, and Applications XIII, 95280I (21 June 2015); doi: 10.1117/12.2185006; https://doi.org/10.1117/12.2185006

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