Determination of spherical target center from TLS data based on a method of nonlinear least squares

Terrestrial Laser Scanning (TLS) is a high-precision measurement technique, which has been widely used in many fields. Since large objects cannot be measured from one station, the data from multiple stations need to be connected together. The common target approach is the widely used. In TLS, targets are used in the registration, geo-referencing, and also as check points, therefore their positioning accuracy directly affects the precision of data processing results. As a spherical target can be scanned from any direction, it is more widely used than a plane target. This paper model the surface of a target by using the Levenberg-Marquardt method of nonlinear least squares to acquire the coordinates of the target centres. Comparing the obtained radius to the given one, we can evaluate the proposed method. The precise determination of target centres can provide accurate data for three-dimensional modelling.