Evaluation of a Terrestrial Laser Scanner According to the ISO 17123-9 Standard

Abstract

Currently, the use of terrestrial laser scanners (TLSs) for point cloud recording is widespread in the fields of architecture, engineering, and construction (AEC), with dimensional tolerance requirements ranging from a few millimeters to several centimeters. The technical specifications of TLSs define the nominal three-dimensional (3D) point accuracy based on distance. In practice, both the design of the TLS and the proprietary software calculation algorithms are key factors in the competition between manufacturers and are therefore not public. This, together with the multiple determinants of each type of work, makes it difficult to assume those values; so, it becomes necessary to use external models to study TLS error sources and standardized evaluation test procedures to determine and evaluate the precision of a TLS and its measurement uncertainties. In this work, we use the international standard ISO 17123-9 to evaluate a Leica TLS RTC360 scanner. We consider observation distances from 10 to 50 m, and use targets with different sizes and reflectance values measured with a Micro-Hyperspec hyperspectral camera. The results show that the use of optimal materials increases the range of the instrument used to automatically detect targets. Additionally, the uncertainties range between 2.7 and 3.9 mm (distances between 10 and 40 m), reaching values of 7.7 mm when the distance is extended to 50 m. Finally, some recommendations for improving the field procedure of this standard are described, with a focus on the interests of surveyors and highlighting the importance of the type of target used. The terrestrial laser scanner has become one of the standard instruments used for surveyor data collection. Like any instrument, the scanner exhibits measurement uncertainties and limitations. A professional surveyor is always concerned about instrument condition imposing possible negative repercussions on their work. This study presents a way to check the condition of the TLS and its auxiliary equipment using the ISO 17123-9 standard, which is a standard made specifically for that purpose. The professional surveyor will certainly find references to this standard in the technical specifications provided by the survey instrument manufacturer. The surveyor should be aware of this family of standards, and, in the specific case of TLS, the importance of auxiliary equipment (e.g., positioning targets), both the material they are made of and their position in relation to the scanner and environmental conditions.