Abstract
Recent years have witnessed emerging the cutting-edge method for point cloud creation using terrestrial laser scanner (TLS). The TLS manufacturers declare accuracies of their instruments up to the millimeter level. However, different constraints could degrade the accuracy of point cloud created by TLS. One of the obvious factors that may directly affect the accuracy of the results is a method of registration and georeferencing. In this paper, the indirect georeferencing using GNSS has been researched. The real time kinematic (RTK) technique has been suggested to measure GNSS points. The conducted test shows that average of 30 minutes data RTK-GNSS is enough to coincide with TLS data. Also, test reveals no improvements when adding more GNSS points. Nevertheless, there is an improvement in accuracy when more scans are conducted.
Highlights
The principle of terrestrial laser scanner (TLS) operation is based on the transmission of a laser beam from a TLS instrument with visible light or near Infrared which is reflected by objects and return to the instrument, and the distance (R) is determined by the time of flight (TOF) or by the phase difference
Georeferencing is required if the TLS point clouds need to be integrated with other geospatial data or sequent of scans need to be related to the same system
The Root Square Errors (RSE) for fitting of different georeferencing are shown in Fig. 5 and Fig. 6 (Note: The MATLAB script is not designed to solve multiple scans, so there are no solutions for Re5 and Re6 by this script)
Summary
The principle of TLS operation is based on the transmission of a laser beam from a TLS instrument with visible light or near Infrared which is reflected by objects and return to the instrument, and the distance (R) is determined by the time of flight (TOF) or by the phase difference. The vertical angle (Φ) and horizontal angle (θ) are determined and combined with distance. Cartesian coordinates (x, y, z) of objects is obtained from distance R and angle θ and Φ as follows (Armesto et al, 2010, Reshetyuk, 2009): xi Ri Cos∅i Cosθi. Where Ri, φj and θi are the measured distance, horizontal and vertical angle, respectively, to the i-th point in the point cloud, and (xi, yi, zi) are its rectangular (Cartesian) coordinates in the scanner coordinate system. To benefit from the created point clouds, it should be related to known coordinate system
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