Resection method for direct georeferencing in Terrestrial Laser Scanner

Recently, the direct georeferencing method has been increasingly used in Terrestrial Laser Scanner (TLS). This method has the benefit of saving time, but the low accuracy is a great difficulty to use. This paper proposed a possible approach for direct georeferencing with high accuracy using the resection method. Thanks to new series of TLS combined with a total station called the total station scanner, the resection method can be applied to overcome the problem. However, the assessment of the resection method on the quality of the point cloud is lacking up to now. In this paper, the influence of components of error sources in the resection method on the total error of the point cloud is analyzed. In the experiment, a Topcon GTL-1000 total station scanner was employed. A ground control network and checkered targets were established by a Leica TS06 plus total station. The experimental results verify that the total error of point cloud entirely agrees with the theory about georeferencing using the resection method. In addition, the distance and incidence angle from the scanner to the measured object are the main factors that considerably influence the accuracy of the point cloud. The relationship between these factors and the accuracy of the point cloud is non-linear measured by a coefficient of determination (R2>0.7). Using the resection method, the coordinates of the scan station can obtain at a millimeter level in accuracy. As a result, the resection method is one of the most suitable methods that can be applied for georeferencing in TLS. The high accuracy and saving time for TLS data post-processing in the office are enormous benefits of this method.