Optimization of two GPS/MEMS-IMU integration strategies with application to sports

The application of low-cost L1 GPS receivers integrated with micro-electro-mechanical system (MEMS) inertial measurement units (IMU) allows the continuous observation of position, velocity and orientation which opens new possibilities for comparison of athletes' performance throughout a racecourse. In this paper, we compare loosely and closely coupled integration strategies under realistic racing scenarios when GPS is partially or completely masked. The study reveals that both integration approaches have a similar performance when the satellite constellation is completed or the outages are short. However, for less than four satellites, the closely coupled strategy clearly outperforms the loosely coupled approach. The second part of the paper is devoted to the important problem of system initialization, because the conventional GPS/IMU alignment methods are no longer applicable when using MEMS-IMU. We introduce a modified coarse alignment method and a quaternion estimation method for the computation of the initial orientation. Simulations and practical experiments reveal that both methods are numerically stable for any initial orientation of the sensors with the error characteristics of MEMS-IMUs. Throughout the paper, our findings are supported by racing experiments with references provided in both, the measurement and the navigation domain

Reliability of Direct Georeferencing Phase 1: An Overview of the Current Approaches and Possibilities., Checking and Improving of Digital Terrain Models / Reliability of Direct Georeferencing.

After some initial hesitations, the direct georeferencing (DG) of airborne sensors by GPS/INS is now a widely accepted approach in the airborne mapping industry. Implementing DG not only speeds up the mapping process and thus increases the productivity, but also opens the door to new monitoring applications. Although the system manufactures tend to claim that DG is a well established technique and no longer a research topic, the technology users often encounter pitfalls due to undetected sensor behavior, varying data quality and consistency. One could almost clair that the reliability of DG is the Achilles'heel of this otherwise revolutionary approach in civil airborne mapping. EuroSDR has recognized this problem and would like to address it in several phases. First phase of this effort are some preliminary investigations, charting the current situation and making suggestions for further research. The investigations are divided into the following technology fields: GNSS, inertial sensors and estimation methods, integrity and communication, calibration and integrated sensor orientation. Each field describes the current situation with respect to DG and discusses additional existing possibilities. These do not claim to be complete or exhaustive; however, they claim to address the essential features, methods and processes, the combination of which could increase the reliability of DG substantially without setting large side penalties

Towards A More Rigorous Boresight Determination: Theory, Technology and Realities of Inertial/GPS Sensor Orientation

This work focuses on the stochastic properties of boresight determination between a strapdown IMU and a frame-based imaging sensor. The core of the stochastic model is a rigorous error propagation of the estimated input accuracies and their correlations

GPS/INS Integrity in Airborne Mapping

The quality of the laser point cloud georeferencing in airborne laser scanning missions is largely related to the quality of the GPS solution. The latter is obtained by post- processing the differential carrier-phase measurements in order to reach the required accuracy. This implies that errors or unacceptable quality in the gathered data that cause problems for the ambiguity resolution in the post- processing step are detected much later. The objective of this thesis is to investigate new concepts of GPS data quality monitoring and to improve the GPS solution by using RAIM and WAAS/EGNOS integrity enhancement techniques. To do that, quality check algorithms based on indicators such as the signal-to-noise ratio, the cycle slip detection results or the phase tracking loop output are proposed and successfully tested. Furthermore, a new global quality check algorithm based on RAIM and cycle slip detection has been designed and tested with a focus on the chances to resolve correctly the ambiguities during the carrier-phase post-processing. The algorithms are implemented in a real- time quality check tool developed in a C/C++ environment whose performance shows that the provided quality indications enhance the GPS integrity by providing crucial information on the signal quality during the flight. This information enables problematic epoch identification and warns immediately the mission operator about problematic flightlines that should be flown again. This avoids final product quality degradation or expensive mission repetition. The thesis also presents the design of an RTK- GPS on-board solution via radio communication channel. The design has been tested during a flight and the results show that a sub-decimetric accuracy can be reached by this mean. The potential of using such a solution is high since this provides ultimate integrity test for phase data. Also, as the final laser point cloud has been georeferenced quite accurately using the real-time sensor observations and Kalman filtering, the economical gain of avoiding post- processing is substantial

Towards Automated LiDAR Boresight Self-calibration

This paper focuses on practical aspects when performing boresight calibration in airborne laser scanning using rigorous methodology implemented in LIBOR software. LIBOR technique, introduced by (Skaloud and Lichti, 2006), is based on expressing the boresight calibration parameters within the direct-georeferencing equation separately for each target point and conditioning a group of points to lie on a common planar surface. Although there is no need for a priori information about the plane parameters as these are part of the unknowns, good estimation requires implication of various planar features that differ in slope and orientation. Such conditions are typically fulfilled in residential-urban areas where the presence of planes in form of roof-tops is abundant. These are identified by grouping points belonging to the same surface into a distinct class separately for each flight line and finding class-correspondences among the flight lines. We present an automated approach for this selection process that stems from intrinsic geometry of curved surfaces. This classification is followed by additional fine-filtering for returns from features as chimneys, antennas etc. The presented discussion focuses on practical examples with data from continuously-rotating and oscillating-mirror systems. These findings show that good automated point selection is possible and acts as a pre-requisite to robust estimates of all boresight angles with accuracy that is several times superior to the system noise level

Optimization of two GPS/MEMS-IMU integration strategies with application to sports

The application of low-cost L1 GPS receivers integrated with micro-electro-mechanical system (MEMS) inertial measurement units (IMU) allows the continuous observation of position, velocity and orientation which opens new possibilities for comparison orf athletes' performance throughout a racecourse. In this paper, we compare loosely and closely coupled integration strategies under realistic racing scenarios when GPS is partially or completely masked. The study reveals that both integration approaches have a similar performance when the satellite constellation is completed or the outages are short. However, for less than four satellites, the closely coupled strategy clearly outperforms the loosely coupled approach. The second part of the paper is devoted to the important problem of system initialization, because the conventional GPS/IMU alignment methods are no longer applicable when using MEMS-IMU. We introduce a modified coarse alignment method and a quaternion estimation method for the computation of the initial orientation. Simulations and practical experiments reveal that both methods are numerically stable for any initial orientation of the sensors with the error characteristics of MEMS-IMU's. Throughout the paper, our findings are supported by racing experiments with references provided in both, the measurement and the navigation domain

UAV Sensor Orientation with Pre-calibrated Redundant IMU/GNSS Observations: Preliminary Results

n unserem Beitrag stellen wir eine Drohne vor, welche für eine hochpräzise Kartographie mit Positions- und Orientierungssensoren ausgestattet ist. Der Einsatz der Sensoren als absolute und relative Messung kann die Genauigkeit des Mappings erhöhen, falls die Sensoren korrekt kalibriert sind. Dies zeigen wir an einem Fallbeispiel, in dem eine Blockstruktur beflogen wurde, in welcher Passpunkte (Ground Control Points) nur lokal angelegt wurden. Eine redundante Sensor-Konfiguration zeigt dann auf, wie gut und genau die Kalibrierung und dessen Resultat sind

Rigorous Integration of Inertial Navigation with Optical Sensors by Dynamic Networks

This paper presents a new concept for simultaneous modeling and adjusting of raw inertial observations with optical and (if available) GNSS data streams. The presented post-mission procedure of dynamic networks allows treating dynamic (e.g. inertial) and static (e.g. optical) raw observations with a spatial-temporal complexity that cannot be expressed in the traditional form of optimal filtering/smoothing. The theory is supported by a simulation scenario of terrestrial mobile mapping where sections of trajectory lacking GNSS coverage are visited several times and the optical observations (ranges and angles) are optimally combined, by using the presented approach, with angular and specific force observations of an onboard IMU. This simulation reveals that the parameter and covariance estimation via dynamic networks is i) equal to that obtained by the conventional INS/GNSS (if available) integration via filtering/optimal smoothing; and, ii) largely superior to the smoother when positioning states are conditioned across different times thanks to optical observations

Rigorous approach to bore-sight self-calibration in airborne laser scanning

We present a rigorous method for estimating some of the calibration parameters in airborne laser scanning (ALS), namely the three bore-sight angles and the range-finder offset. The technique is based on expressing the system calibration parameters within the direct-georeferencing equation separately for each target point, and conditioning a group of points to lie on a common surface of a known form such as plane

High accuracy handheld mapping system for fast helicopter deployment

This paper presents a self-contained, light and flexible mapping system that can be quickly deployed into inaccessible areas. Although designed to measure wind-transported snow volumes and the snow avalanche runoff over and experimental site, the system is suitable to any large-scale 3-D terrain mapping