Determination of the optimal diameter for spherical targets used in 3D laser scanning

An efficient use of 3D laser scanning requires the development of standardized calibration procedures available to the users. This is part of the research recently started at the Royal Institute of Technology; (KTH) in Stockholm and the establishment of a calibration field is planned, which may he realized by means of spherical targets. An approach for the rigorous theoretical determination of the optimal diameter for those targets is presented. It is based on the least-squares adjustment according to the mixed model when observations are combined with the unknown parameters. The weight function was chosen based on the Lambertion standard reflectance model. The computations were performed for the scanners Leica HDS 3000 and Imager 5003 (Zoller+Frohlich) for two cases - with fixed and "free" (to be estimated in the adjustment) target diameter. The value of 14 cm has been obtained for the optimal diameter, which is independent on the range to the scanner.