Comparative Assessment of Terrestrial Laser Scanner Against Traditional Surveying Methods

Ahmed M. Abd-Elmaaboud, Mohamed E. El-Tokhey, Ahmed E. Ragheb, Yasser M. Mogahed

Terrestrial laser scanner has become a familiar instrument and most used technology for rapidly capturing very accurate and highly detailed 3D point cloud datasets for a variety of applications in Engineering. The advantage of laser scanning is that it can record huge numbers of points in a relatively short period of time. The main idea here is to assess the accuracy of terrestrial laser scanner and compare it relative to the other traditional surveying instruments. This was done throughout four different approaches. First, a grid levelling for a 30,000m² ground terrain was performed using Total Station (TS), and Terrestrial Laser Scanner (TLS). After which, the RMSE for TLS was computed. Secondly, a control point network consisting of nine points was measured using TS, TLS, and real time kinematic global positioning system (RTK-GPS) and the precision for each instrument was calculated depending on the standard deviation (SD). In addition, the accuracy of TLS and RTK-GPS was calculated depending on the RMSE.  Thirdly, the effect of vertical angle on TLS measurements was assessed by measuring fifty-six points fixed on a building façade using different vertical angles. Those points were measured using both TS and TLS, then the absolute height differences between TS and TLS measurements were calculated to figure out the effect of increasing the vertical angle on measurements. Finally, the accuracy of TLS on vertical cut measurements was calculated by surveying a downhill area of 500m² by both TS and TLS and the RMSE for TLS measurements was calculated. From the research results, it was found that the RMSE for TLS in measuring terrains was about 15cm. In measuring control point networks, TLS was figured out a higher accuracy than RTK-GPS. TLS vertical angle is not preferable to be more than 45 degrees. In vertical cut measurements TLS was figured out a RMSE of 6mm and a lower measurement period. Eventually, despite the fact that TLS is more expensive than traditional surveying techniques, it is more beneficial in terms of time and effort saving. In addition, it can figure out acceptable accuracy ranges with more detailed surveyed data.