GPS différentiel | EPFL Graph Search

Le GPS différentiel (en anglais Differential Global Positioning System : DGPS) est une amélioration du GPS permettant de passer d'une précision de 15 mètres à 1-3 cm avec les meilleurs implémentations. Il utilise un réseau de stations fixes de référence qui transmet l’écart entre les positions indiquées par les satellites et leurs positions réelles connues. En fait le récepteur reçoit la différence entre les pseudo-distances mesurées par les satellites et les véritables pseudo-distances et peut ainsi corriger ses mesures de positions. Le terme DGPS peut s’appliquer aussi bien à la technique elle-même qu’à des implémentations qui l’utilisent. Par exemple le WAAS de la Federal Aviation Administration (FAA) utilise des techniques différentielles pour améliorer la précision, elles transmettent les corrections par satellite sur la bande L. Parmi les autres exemples de systèmes similaires on trouve le système européen de complément à la navigation géostationnaire EGNOS, le système japonais

Trajectory determination and analysis in sports by satellite and inertial navigation

Adrian Wägli

This research presents methods for performance analysis in sports through the integration of Global Positioning System (GPS) measurements with Inertial Navigation System (INS). The described approach focuses on strapdown inertial navigation using Micro-Electro-Mechanical System (MEMS) Inertial Measurement Units (IMU). A simple inertial error model is proposed and its relevance is proven by comparison to reference data. The concept is then extended to a setup employing several MEMS-IMUs in parallel. The performance of the system is validated with experiments in skiing and motorcycling. The position accuracy achieved with the integrated system varies from decimeter level with dual-frequency differential GPS (DGPS) to 0.7 m for low-cost, single-frequency DGPS. Unlike the position, the velocity accuracy (0.2 m/s) and orientation accuracy (1 – 2 deg) are almost insensitive to the choice of the receiver hardware. The orientation performance, however, is improved by 30 – 50% when integrating four MEMS-IMUs in skew-redundant configuration. Later part of this research introduces a methodology for trajectory comparison. It is shown that trajectories based on dual-frequency GPS positions can be directly modeled and compared using cubic spline smoothing, while those derived from single-frequency DGPS require additional filtering and matching.

EPFL2009

Integrating Multiple GPS Receivers With a Low Cost IMU For Aircraft Attitude Determination

Telmo Cunha, Phillip Tomé

Many airborne applications, such as altimetry or photogrammetry without ground control points, strongly rely on the precise evaluation of the aircraft’s attitude. This paper presents an approach to the attitude determination problem, where a system combining Litton’s LN-200 Inertial Measurement Unit (IMU) with differential GPS (DGPS) is described. The methodology is based on the integrated processing of raw inertial measurements and GPS data collected from at least two receivers on board the aircraft and one, or possibly more, reference stations. It is well known that GPS and inertial navigation systems have complementary operational characteristics that can be exploited in an integrated system for continuous tracking of the aircraft’s navigational parameters (attitude, velocity and position). The incorporation of DGPS observations of one of the aircraft’s GPS antennas, specifically absolute position and doppler velocity readings, improves the overall system accuracy, including the estimates of roll and pitch angles that result from filtered raw inertial measurements, since it enables the continuous alignment of the strapdown analytical platform. By processing carrier phase measurements in differential mode between a pair of the aircraft’s GPS antennas (without information from any reference station), good attitude observations, especially true heading, are obtained. This is critical to align the low cost inertial platform in heading, since azimuth errors are weakly coupled with velocity or position errors. In fact, by this method alignment is achieved in motion and very quickly. The inertial system also provides high rate (DGPS filtered) position and velocity estimates that can be valuable during GPS signal outages and in DGPS ambiguity fixing procedures that occur whenever a new satellite becomes visible or cycle slips are detected. The estimated accuracy is 0.01º (1s) for roll and pitch and 0.1º (1s) for heading. Should the reference station data be absent and stand-alone doppler and position estimates be used instead, some degradation of the roll and pitch accuracy are to be expected. Besides a description of the relevant theory, this paper also includes post-processing results from one of a series of flights that took place in the Azorean area during a gravimetric and altimetric survey. The present methodology was successfully employed to process all data from this campaign.

1999

Real Time Aircraft Position+Attitude of Airborne Sensors

Telmo Cunha, Phillip Tomé

The determination of instantaneous positions with high accuracy using differential GPS techniques is of great importance for several applications, like airborne topographic mapping, airborne gravimetry and altimetry. In some of these applications long baselines are involved creating additional problems in the correct determination of the position of the sensors. The determination of the attitude of the aircraft is also of great importance in this context. This paper presents a technique that, taking advantage of the integration of GPS and inertial measurements, produces real time positions. The demand for real time positioning introduces some more constraints, which must be taken into account from the start of the algorithm development to the end of its implementation. A methodology for processing GPS and raw data from an inertial measurement unit (IMU) was implemented in a feedback integrated structure. The position determination is based on real time DGPS with L1 and L2 carrier phase ambiguity fixing, using on-line IMU processed data to validate and increase the positions reliability, especially during GPS outages and when the aircraft is far away from the nearest GPS reference station. By processing L1 and L2 carrier phase measurements in differential mode between a pair of the aircraft GPS antennas (without resorting to ground reference station data), a partial estimate of the aircraft attitude is obtained. This is critical to align the low cost inertial platform in heading either when the aircraft is stopped or in flight. In addition, the DGPS absolute positions are used to update the IMU data in real time. By using the proposed methodology it was possible to explore the entire potential of a low cost IMU/GPS system. The position and attitude values are obtained from all the measurements through an extended Kalman filter. Decimeter accuracy was achieved for the positions. For the orientation of the aircraft an accuracy of 0.01º (1) for roll and pitch and 0.1º (1 sigma) for heading was achieved. The performance and the results obtained with this system using data from an airborne campaign that took place in Portugal are discussed.

1999

Real Time Aircraft Position+Attitude of Airborne Sensors

Telmo Cunha, Phillip Tomé

1999

Integrating Multiple GPS Receivers With a Low Cost IMU For Aircraft Attitude Determination

Telmo Cunha, Phillip Tomé

1999