Signs on glasses: LiDAR data voids, hotspot effect, and reflection artifacts

A key challenge in terrestrial laser scanning (TLS) based as-built survey is the presence of data voids, reflection artifacts, and hotspot effect on glasses. This paper investigates the effects of scanning range, illumination condition, instrument height, and spatial offset of an occluded object between the scanner and glasses with respect to these data artifacts. Experimental results show that ordinary float glass encounters a high percentage of data voids ($>$ 93%) and reflective glass backscatters laser pulses with greater than 50%. Hotspot effect is found notable at azimuth scanning angle between $\pm$ 2 and 5° on both types of glasses. Ordinary float glass never results in any reflection artifacts, while they likely emerge when the scanner is set up at a certain height ($>$ 0.7 m) and a closer range ($\le$ 7.5 m) on the reflective glass. These findings shed light on the future algorithmic development of glass detection, classification, and defects removal.