Influence of Control Points Configuration on the Mobile Laser Scanning Accuracy

Abstract

Mobile mapping systems (MMS) are becoming widely used in standard geodetic tasks more commonly in the last years. The paper is focused on the influence of control points (CPs) number and configuration on mobile laser scanning accuracy. The mobile laser scanning (MLS) data was acquired by MMS RIEGL VMX-450. The resulting point cloud was compared with two different reference data sets. The first reference data set consisted of a high-accuracy test point field (TPF) measured by a Trimble R8s GNSS system and a Trimble S8 HP total station. The second reference data set was a point cloud from terrestrial laser scanning (TLS) using two Faro Focus3D X 130 laser scanners. The coordinates of both reference data sets were determined with significantly higher accuracy than the coordinates of the tested MLS point cloud. The accuracy testing is based on coordinate differences between the reference data set and the tested MLS point cloud. There is a minimum number of 6–7 CPs in our scanned area (based on MLS trajectory length) to achieve the declared relative accuracy of trajectory positioning according to the RIEGL datasheet. We tested two types of ground control point (GCP) configurations for 7 GCPs, using TPF reference data. The first type is a trajectory-based CPs configuration, and the second is a geometry-based CPs configuration. The accuracy differences of the MLS point clouds with trajectory-based CPs configuration and geometry-based CPs configuration are not statistically significant. From a practical perspective, a geometry-based CPs configuration is more advantageous in the nonlinear type of urban area such as our one. The following analyzes are performed on geometry-based CPs configuration variants. We tested the influence of changing the location of two CPs from ground to roof. The effect of the vertical configuration of the CPs on the accuracy of the tested MLS point cloud has not been demonstrated. The effect of the number of control points on the accuracy of the MLS point cloud was also tested. In the overall statistics using TPF, the accuracy increases significantly with increasing the number of GCPs up to 6. This number corresponds to a requirement of the manufacturer. Although further increasing the number of CPs does not significantly increase the global accuracy, local accuracy improves with increasing the number of CPs up to 10 (average spacing 50 m) according to the comparison with the TLS reference point cloud. The accuracy test of the MLS point cloud was divided into the horizontal accuracy test on the façade data subset and the vertical accuracy test on the road data subset using the TLS reference point cloud. The results of this paper can help improve the efficiency and accuracy of the mobile mapping process in geodetic praxis.

Optimizing Mobile Laser Scanning Accuracy for Urban Applications: A Comparison by Strategy of Different Measured Ground Points

“…As mentioned in the "MLS Data Acquisition" Section 2.5, the carrier speed was lower in this test. In the first instance, the speed was 20 km/h, which was chosen for its sufficient accuracy for testing and smoothness of data collection; the same speed is used in [25], where the final accuracy is high. A simple calculation shows that the density of points at 10 m should be 10,250 points/m 2 .…”

“…The object of interest is to test the system in an urban area where the GNSS signal is jammed by surrounding trees and buildings. For this purpose, an extensive test field has been created to satisfy this condition [25,28]. The network is made up of control points, which are used to precisely align the point cloud, and of checkpoints.…”

“…A big issue in mobile mapping is accuracy. In particular, the dependence of accuracy on the frequency and distribution of control points [24,25].…”

“…Thus, the GNSS error is also reflected in the MMS accuracy result. Absolute accuracy is the focus of the paper [25]. In this paper, only a small area is surveyed, but the point field is dense and well-signalled, and the coordinates are accurately measured by an independent method.…”

Space-constrained Mobile Laser-point Cloud Data Acquisition Method

“…The vehicle-mounted laser system integrates multiple sensors to collect information and quickly obtain 3D information on the surface. (14,15) Through the combined calculation of GNSS, INS, and odometer data, the trajectory and attitude of the carrier are determined, and the distance and angle information obtained by the laser scanner are combined to obtain the 3D points of the measured object. When data acquisition is carried out in the outdoor part of a commercial area, the GNSS signal is weak due to the height and density of commercial buildings, and there is no GNSS signal during the data acquisition process in an underground parking lot.…”