Abstract
Abstract. The random error pattern of point clouds has significant effect on the quality of final 3D model. The magnitude and distribution of random errors should be modelled numerically. This work aims at developing such an anisotropic point error model, specifically for the terrestrial laser scanner (TLS) acquired 3D point clouds. A priori precisions of basic TLS observations, which are the range, horizontal angle and vertical angle, are determined by predefined and practical measurement configurations, performed at real-world test environments. A priori precision of horizontal (𝜎𝜃) and vertical (𝜎𝛼) angles are constant for each point of a data set, and can directly be determined through the repetitive scanning of the same environment. In our practical tests, precisions of the horizontal and vertical angles were found as 𝜎𝜃=±36.6𝑐𝑐 and 𝜎𝛼=±17.8𝑐𝑐, respectively. On the other hand, a priori precision of the range observation (𝜎𝜌) is assumed to be a function of range, incidence angle of the incoming laser ray, and reflectivity of object surface. Hence, it is a variable, and computed for each point individually by employing an empirically developed formula varying as 𝜎𝜌=±2−12 𝑚𝑚 for a FARO Focus X330 laser scanner. This procedure was followed by the computation of error ellipsoids of each point using the law of variance-covariance propagation. The direction and size of the error ellipsoids were computed by the principal components transformation. The usability and feasibility of the model was investigated in real world scenarios. These investigations validated the suitability and practicality of the proposed method.
Highlights
Even though the Terrestrial Laser Scanning (TLS) technology provides accurate 3D description of a target object or scene, individual points of the 3D point cloud contains random and gross errors
This paper presents a generic anisotropic point error model for TLS derived point clouds to model magnitude and distribution of random errors numerically
Contrary to other studies, which have focused on positional uncertainty of individual points, this paper presents a practical error model which takes into account both a priori angular and range measurement precisions
Summary
Even though the Terrestrial Laser Scanning (TLS) technology provides accurate 3D description of a target object or scene, individual points of the 3D point cloud contains random and gross errors. Contrary to other studies, which have focused on positional uncertainty of individual points, this paper presents a practical error model which takes into account both a priori angular and range measurement precisions. Another contribution of the paper is definition of the a priori range precision as a function of object distance, incidence angle and. A priori precisions of basic TLS observations were determined by practical measurement configurations, which were performed at real-world test environments This procedure was followed by computation of error ellipsoid of each individual point using the law of variance-covariance propagation.
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