On the applicability of a scan-based mobile mapping system for monitoring the planarity and subsidence of road surfaces – Pilot study on the A44n motorway in Germany

Abstract

Kinematic laser scanning is widely used for the fast and accurate acquisition of road corridors. In this context, road monitoring is a crucial application, since deficiencies of the road surface due to non-planarity and subsidence put traffic at risk. In recent years, a Mobile Mapping System (MMS) has been developed at the University of Bonn, consisting of a GNSS/IMU unit and a 2D laser scanner. The goal of this paper is to evaluate the accuracy and precision of this MMS, where the height component is of main interest. Following this, the applicability of the MMS for monitoring the planarity and subsidence of road surfaces is analyzed. The test area for this study is a 6 km long section of the A44n motorway in Germany. For the evaluation of the MMS, leveled control points along the motorway as well as point cloud comparisons of repeated passes were used. In order to transform the ellipsoidal heights of the MMS into the physical height system of the control points, undulations were utilized. In this respect, a local tilt correction for the geoid model was determined based on GNSS baselines and leveling, leading to a physical height accuracy of the MMS of < 10 mm (RMS). The related height precision has a standard deviation of about 5 mm. Hence, a potential subsidence of the road surface in the order of a few cm is detectable. In addition, the point clouds were used to analyze the planarity of the road surface. In the course of this, the cross fall of the road was estimated with a standard deviation of < 0.07 %. Yet, no deficiencies of the road surface in the form of significant rut depths or fictive water depths were detected, indicating the proper condition of the A44n motorway. According to our tests, the MMS is appropriate for road monitoring.

Design and Evaluation of a Permanently Installed Plane-Based Calibration Field for Mobile Laser Scanning Systems

“…This accuracy applies to the measuring conditions in our evaluation environment and might change for other fields of applications. Please note that the obtained evaluation results for our mobile laser scanning system are in good accordance with the results that were obtained in a prior case study on a motorway [59].…”

“…The evaluation strategies for analyzing the accuracy of mobile laser scanning systems can be classified into point-based, area-based, and parameter-based methods. Point-based methods use either natural control points (e.g., building corners, manholes, poles, or road markings) or artificial control points (e.g., targets or markers), which are extracted from the 3D point clouds and compared to reference values that were determined by other surveying methods like total stations, leveling, GNSS, or TLS (e.g., [18][19][20][21]26,28,29,31,33,[55][56][57][58][59]). Such methods assess the absolute accuracy of a system as a whole, instead of analyzing individual components.…”

“…Furthermore, reference point clouds (e.g., from TLS) are commonly used for evaluation (e.g., [10,11,18,21,33,[63][64][65]), since software packages provide algorithms for the comparison of two point clouds. In this regard, it is also possible to mesh patches of the road surface that were measured multiple times with the mobile laser scanning system and compare these patches to each other [19,59]. Area-based evaluation methods supplement the point-based strategies, as mobile laser scanning is an area-based measuring technology.…”

“…Geometric parameters of road surfaces, building structures, or objects can repeatedly be extracted from the point clouds of multiple passes. The repeatability of such parameters also indicates the quality of a system (e.g., [18,59,66]).…”

“…A more detailed view of the system is given in Figure 2. A case study on a motorway showed that the accuracy of the system is about millimeter to centimeter under good GNSS conditions [59].…”