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Assessment of Terrestrial Laser Scanner against Different Surveying Techniques.( Dept. C)

Terrestrial Laser Scanner (TLS) has become a familiar instrument to be used in wide range of engineering application. It can be used for the rapid capture of accurate and highly detailed 3D point cloud datasets. The advantage of laser scanner is that it can record huge number of points in a short period of time. The main idea in this contribution assesses the accuracy of TLS relative to other traditional surveying instruments. This is done throughout four different case studies. In all case studies the 3D coordinates, obtained using total station (TS) are assumed the reference coordinates. First, a control point network, that consists of nine points, is measured using TS, TLS, and real time kinematic global navigation satellite system (RTK-GPS). The precision of each instrument is investigated considering the standard deviation (SD) of measurements. In addition, the accuracy of TLS and RTK-GPS is investigated considering the measurements RMS. Secondly, a grid levelling for a 30,000m2 ground terrain was performed using TS and TLS. After words, the RMS of TLS measurements is computed and a grid of 5mx5m is generated from both surfaces; formed using TS and TLS measurements.  Thirdly, the effect of incidence angle on TLS measurements is assessed by measuring fifty-six points fixed on a building facade using different incident angles. Those points were measured using both TS and TLS, and then the absolute height differences between TS and TLS measurements were calculated to figure out the effect of decreasing the incidence angle on measurements. In the fourth case study, the accuracy of TLS on steep-vertical cut measurements is investigated by surveying a downhill area of 500m2 by both TS and TLS, the RMS of TLS measurements was calculated. Finally, based on the obtained results, it was found that TLS produces a higher vertical accuracy than RTK-GPS in measuring control point networks. The RMS of TLS measurements was about 5cm. Moreover, TLS incidence angle is not preferable to be less than 45 degrees as the accuracy degrades significantly after this value. In steep-vertical cut measurements, TLS obtained RMS almost of 6mm discrepancies with 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.