Raw GPS Research Articles

Detecting Significant Locations from Raw GPS Data Using Random Space Partitioning

Detecting Significant Locations from Raw GPS Data Using Random Space Partitioning

Detecting Significant Locations from Raw GPS Data Using Random Space Partitioning

Detecting Significant Locations from Raw GPS Data Using Random Space Partitioning

都市部におけるRTK-GPSの信頼性向上

It is expected that the use of GNSS technology in urban areas will be increased. Since there are many buildings in urban areas, the direct signal from satellite occasionally can be reflected or diffracted. As a result, we are faced with big errors due to multipath. It is strongly required to improve reliability considering the use of GNSS for future ITS. In order to do that, the ability to detect the inferior observations of GNSS is required. The objective of this paper is to improve reliability and availability in RTK-GPS. Firstly, this study reveals the relationships between reliability and availability according to the quality check of GPS observation data. For example, reliability decreases when the measurement calculation is done with four numbers of satellites compared with five numbers or more of satellites. Then the detection algorithm to remove the inferior observations of GPS is proposed. The performance was checked by using raw GPS data obtained in major cities and it is confirmed that the performance was improved by using our proposed method.

On Modelling of Second-Order Ionospheric Delay for GPS Precise Point Positioning

Recent developments in GPS positioning show that a user with a standalone GPS receiver can obtain positioning accuracy comparable to that of carrier-phase-based differential positioning. Such technique is commonly known as Precise Point Positioning (PPP). A significant challenge of PPP, however, is that about 30 minutes or more is required to achieve centimetre to decimetre-level accuracy. This relatively long convergence time is a result of the un-modelled GPS residual errors. A major residual error component, which affects the convergence of PPP solution, is higher-order Ionospheric Delay (IONO). In this paper, we rigorously model the second-order IONO, which represents the bulk of higher-order IONO, for PPP applications. Firstly, raw GPS measurements from a global cluster of International GNSS Service (IGS) stations are corrected for the effect of second-order IONO. The corrected data sets are then used as input to the Bernese GPS software to estimate the precise orbit, satellite clock corrections, and Global Ionospheric Maps (GIMs). It is shown that the effect of second-order IONO on GPS satellite orbit ranges from 1·5 to 24·7 mm in radial, 2·7 to 18·6 mm in along-track, and 3·2 to 15·9 mm in cross-track directions, respectively. GPS satellite clock corrections, on the other hand, showed a difference of up to 0·067 ns. GIMs showed a difference up to 4·28 Total Electron Content Units (TECU) in the absolute sense and an improvement of about 11% in the Root Mean Square (RMS). The estimated precise orbit clock corrections have been used in all of our PPP trials. NRCan's GPSPace software was modified to accept the second-order ionospheric corrections. To examine the effect of the second-order IONO on the PPP solution, new data sets from several IGS stations were processed using the modified GPSPace software. It is shown that accounting for the second-order IONO improved the PPP solution convergence time by about 15% and improved the accuracy estimation by 3 mm.

Estimation of Road Centerline Curvature from Raw GPS Data

Development and wide use of route guidance systems lead to the need for suitable digital maps that can be used for some advanced applications. Sufficient accuracy of road geometry with emphasis on road centerline positions and curvature is crucial. In this paper is presented a method for finding road centerline curvature from raw GPS data. The approach consists of a few processing steps. First it is necessary to fit raw data of each road section using B-splines, and generate equidistant vertices of polyline of the fitted curve. Then follows the appliance of stereographic projection of chosen polyline segments onto the unit sphere. Using the least square method, the plane that best fits the points on the unit sphere is found and the circle that is the intersection of the plane and the unit sphere. Stereographic projection of this circle back to the equatorial plane gives the corresponding circular arc and curvature. The method is also applicable in higher dimensions. The 3D case is numerically presented and results show that the proposed procedure is efficient and yields accurate results.

Detecting Large-scale Intracontinental Slow-slip Events (SSEs) Using Geodograms

Since the advent in the 1980s of GPS networks to monitor crustal velocity fields, interpretations of geodetic data have generally been based on maps of Earth's surface showing average horizontal site velocity over a specified period of time and plots showing velocity gradients as a function of a position coordinate (e.g., Donnellan et al. 1993; Bennett et al. 1999). For continuous networks, these plots are typically supplemented by time series of position in order to assess the importance of time-dependent or transient behavior (Bock et al. 1993; Hudnut et al. 2002). Thus far, regional transient motions have been revealed by plotting position time series from multiple sites on a common time axis. These plots have been effective in demonstrating the existence of slow-slip events (SSEs) on subduction megathrust interfaces around the globe (e.g., Miller et al. 2002; Melbourne et al. 2005; Schwartz and Rokosky 2007). A large-scale intraplate SSE in the northern Basin and Range Province that occurred between 1999 and 2005 was initially identified by plotting continuous time series with a vertical time axis, arranged according to a spatial position coordinate for each site (Davis et al. 2006, their Figure 3A). Because transient motions are by definition changes in velocity, however, the spatial coherence and magnitude of velocity changes are most directly addressed by plotting the time dependence of velocity rather than position. Here, we describe a method for calculating velocity time series, and then we use these to construct a geodogram from raw continuous GPS time series. The new time series reveal additional transient motions from 2005 to 2007 that are interpreted to reflect the onset of a new SSE beginning in late 2006.

Usefulness of commercially available GPS data-loggers for tracking human movement and exposure to dengue virus

BackgroundOur understanding of the effects of human movement on dengue virus spread remains limited in part due to the lack of precise tools to monitor the time-dependent location of individuals. We determined the utility of a new, commercially available, GPS data-logger for long-term tracking of human movements in Iquitos, Peru. We conducted a series of evaluations focused on GPS device attributes key to reliable use and accuracy. GPS observations from two participants were later compared with semi-structured interview data to assess the usefulness of GPS technology to track individual mobility patterns.ResultsPositional point and line accuracy were 4.4 and 10.3 m, respectively. GPS wearing mode increased spatial point error by 6.9 m. Units were worn on a neck-strap by a carpenter and a moto-taxi driver for 14-16 days. The application of a clustering algorithm (I-cluster) to the raw GPS positional data allowed the identification of locations visited by each participant together with the frequency and duration of each visit. The carpenter moved less and spent more time in more fixed locations than the moto-taxi driver, who visited more locations for a shorter period of time. GPS and participants' interviews concordantly identified 6 common locations, whereas GPS alone identified 4 locations and participants alone identified 10 locations. Most (80%) of the locations identified by participants alone were places reported as visited for less than 30 minutes.ConclusionThe present study demonstrates the feasibility of a novel, commercially available GPS data-logger for long-term tracking of humans and shows the potential of these units to quantify mobility patterns in relationship with dengue virus transmission risk in a tropical urban environment. Cost, battery life, size, programmability and ease of wear are unprecedented from previously tested units, proving the usefulness of GPS-dataloggers for linking movement of individuals and transmission risk of dengue virus and other infectious agents, particularly in resource-poor settings.

Assessment of stochastic models for GPS measurements with different types of receivers

The stochastic model plays an important role in parameter estimation. The optimal estimator in the sense of least squares can only be obtained by using the correct stochastic model and consequently guarantees the precise positioning in GPS applications. In this contribution, the GPS measurements, collected by different types of geodetic dual-frequency receiver pairs on ultra-short baselines with a sampling interval of 1 s, are used to address their stochastic models, which include the variances of all observation types, the relationship between the observation accuracy and its elevation angle, the time correlation, as well as the correlation between observation types. The results show that the commonly used stochastic model with the assumption that all the raw GPS measurements are independent with the same variance does not meet the need for precise positioning and the elevation-dependent weight model cannot work well for different receiver and observation types. The time correlation and cross correlation are significant as well. It is therefore concluded that the stochastic model is much associated with the receiver and observation types and should be specified for the receiver and observation types.

Quantification of strain rate in the Western Alps using geodesy: comparisons with seismotectonics

The contrasted seismotectonic regime of the Western Alps is characterized by radial extension in the high chain, combined with local compressive areas at the foothill of the belt, and everywhere occurrence of transcurrent tectonics. Here, we compare this seismotectonic regime to a large-scale compilation of GPS measurements in the Western Alpine realm. Our analysis is based on the raw GPS database, which give the measured velocity field with respect to the so called “stable Europe”, and an interpolated velocity field, in order to smooth the database on a more regular mesh. Both strain rate and rotational components of the deformation are investigated. The strain rate field shows patch-like structure, with extensional areas located in the core and to the North of the belt and compressional areas located in its periphery. Although the GPS deformation fields (both raw and interpolated) are more spatially variable than the seismotectonic field, a good qualitative correlation is established with the seismotectonic regionalization of the deformation. The rotation rate fields (both raw and interpolated) present counterclockwise rotations in the innermost part of the belt and a surprising continuous zone of clockwise rotations following the arc-shape geometry of the Western Alps along their external border. We interpret this new result in term of a counterclockwise rotation of the Apulia plate with respect to the stable Europe. This tectonic scheme may induce clockwise rotations of crustal block along the large strike-slip fault system, which runs in the outer part of the belt, from the Rhône-Simplon fault to the Belledonne fault and Southeastward, to the High-Durance and Argentera fault.

Potential for issuing ionospheric warnings to Canadian users of marine DGPS

Under normal operating conditions marine DGPS horizontal positioning accuracies on the order of several meters are achieved in North America. Degradations in positioning accuracy can occur during enhanced ionospheric activity. An ionospheric phenomenon known as storm enhanced density (SED) is observed to develop in the middle to high latitudes during ionospheric storm events. Very large gradients in total electron content are observed in the vicinity of this feature with DGPS positioning errors increased by a factor of 10–30 versus quiet conditions. The specific evolution of a given SED event and the magnitude of expected impact are not generally predictable. A method to monitor development of SED is to compute ionospheric maps in real time. Local gradients can then be computed for various geographic regions from North American maps of ionospheric delay. Sources of real‐time ionospheric information include the Wide Area Augmentation System (WAAS) and the Canadian GPS•C service. These are wide area differential GPS systems. In this paper, a real‐time ionospheric warning system is investigated for North American (primarily Canadian) DGPS users based on available real‐time data. The WAAS and GPS•C ionospheric models are inadequate to resolve ionospheric gradients for 100–200 km scale sizes. Raw GPS data from GPS•C reference sites can be used, however, to observe large ionospheric gradients and interpret the expected impact on DGPS users. Potential exists to issue marine user warnings based on this method. Results of this work can readily be extended to land DGPS applications, such as the NDGPS service in the United States.

Hierarchical Route Representation, Indexing, and Search

This information-retrieval system uses raw GPS traces collected from numerous drivers to represent, index, and search routes and can support efficient full-text search under varying conditions.

Optimal carrier-smoothed-code algorithm for dual-frequency GPS data

Carrier-smoothed-code (CSC) algorithm is an effective pseudorange multipath mitigation technique, which can alleviate the computational burden and reduce the communication bandwidth needed for the transmission of GPS observations. This paper presents an improved Hatch filter and addresses the optimal CSC algorithm for dual-frequency GPS data based on the optimal parameter estimation theory. The smoothed observations have the same information content as that of the raw dual-frequency GPS data from which these are derived. Consequently, the optimal CSC algorithm is equivalent to the uncombined algorithm. Theoretical analyses show that the data precision of the optimal CSC algorithm is better than that of Hatch filter and its improved version.

Improved Estimation of ADCP Apparent Bed-Load Velocity Using a Real-Time Kalman Filter

An estimate of apparent bed-load velocity (v) can be derived from the difference between differential global positioning system (DGPSs) and acoustic Doppler current profiler (ADCP) bottom track (BT) measurements when BT is biased by a moving bottom. A Kalman filter has been developed to integrate GPS and bottom track data to improve estimation of boat velocity during ADCP measurements under moving bed conditions (Rennie and Rainville, 2008, J. Hydraulic Eng., in review). The boat velocity estimated using the Kalman filter is superior to boat velocity from raw GPS data. In this paper we assess the improvement in estimation of v using the Kalman filter as opposed to raw GPS data. Specifically, a synthetic moving bed bias was generated for 22 repeat transects of the Gatineau River, Quebec. The synthetic moving bed bias had mean, variance, and distribution across the section as typically observed during bed-load transport conditions, and had the advantage that it was known explicitly. The errors in estimated ...

Learning and inferring transportation routines

This paper introduces a hierarchical Markov model that can learn and infer a user's daily movements through an urban community. The model uses multiple levels of abstraction in order to bridge the gap between raw GPS sensor measurements and high level information such as a user's destination and mode of transportation. To achieve efficient inference, we apply Rao–Blackwellized particle filters at multiple levels of the model hierarchy. Locations such as bus stops and parking lots, where the user frequently changes mode of transportation, are learned from GPS data logs without manual labeling of training data. We experimentally demonstrate how to accurately detect novel behavior or user errors (e.g. taking a wrong bus) by explicitly modeling activities in the context of the user's historical data. Finally, we discuss an application called “Opportunity Knocks” that employs our techniques to help cognitively-impaired people use public transportation safely.

Redundant multi-mode filter for a navigation system

An approach is introduced to the design of a multi-mode navigation filter to combine a low-cost skewed redundant inertial measurement unit (SRTMU) with a multifunctional GPS (MF-GPS) receiver in order to implement a fault-tolerant aircraft navigation system, which can achieve the required navigation performance of conventional systems in terms of accuracy, integrity, continuity, and availability. The MF-GPS receiver provides raw GPS measurements for pseudo-range and range rate to compute the navigation solutions (position and velocity) and also multi-antenna carrier phase interferometric measurements to estimate the aircraft attitude solution, if the carrier phase data is reliable. A multi-mode navigation filter is designed which combines state and measurement fusion methods and processes the SRIMU and raw MF-GPS outputs to provide reliable position, velocity and attitude information, and also kinematic parameters required in control, guidance, and navigation applications. The feasibility and performance of this integrated design is assessed and evaluated by using simulation. The accuracy of inertial gyros used in the evaluation ranges from ldeg/h to 30deg/h, including low-cost inertial sensor technologies. The simulation studies presented here show that a multi-mode navigation filter can achieve sufficient reliability and accuracy and that SRIMU/MF-GPS integrated navigation systems may provide a cost-effective system for future regional aircraft, general aviation aircraft, and unmanned aerial vehicles

Building Personal Maps from GPS Data

In this article we discuss an assisted cognition information technology system that can learn personal maps customized for each user and infer his daily activities and movements from raw GPS data. The system uses discriminative and generative models for different parts of this task. A discriminative relational Markov network is used to extract significant places and label them; a generative dynamic Bayesian network is used to learn transportation routines, and infer goals and potential user errors at real time. We focus on the basic structures of the models and briefly discuss the inference and learning techniques. Experiments show that our system is able to accurately extract and label places, predict the goals of a person, and recognize situations in which the user makes mistakes, such as taking a wrong bus.

Using tracked mobile sensors to make maps of environmental effects

We present the results of a study of environmental carbon monoxide pollution that uses a set of tracked, mobile pollution sensors. The motivating concept is that we will be able to map pollution and other properties of the real world at a fine scale if we can deploy a large set of sensors with members of the general public who would carry them as they go about their normal everyday activities. To prove the viability of this concept we have to demonstrate that data gathered in an ad hoc manner is reliable enough in order to allow us to build interesting geo-temporal maps. We present a trial using a small number of global positioning system-tracked CO sensors. From analysis of raw GPS logs we find some well-known spatial and temporal properties of CO. Further, by processing the GPS logs we can find fine-grained variations in pollution readings such as when crossing roads. We then discuss the space of possibilities that may be enabled by tracking sensors around the urban environment—both in getting at personal experience of properties of the environment and in making summative maps to predict future conditions. Although we present a study of CO, the techniques will be applicable to other environmental properties such as radio signal strength, noise, temperature, humidity and so on.

Airborne gravity over Lake Vostok and adjacent highlands of East Antarctica

Lake Vostok and a 1200 km transect were the targets of aerogeophysical surveys in East Antarctica during the austral summer of 2000/2001. The measurement of gravity anomalies for geologic studies was the primary goal. A total of 24,459 line‐km of data were acquired. Favorable weather, aircraft navigation, and instrument performance contributed to excellent data quality. Multiple carrier‐phase GPS solutions to determine aircraft‐induced accelerations were available for each flight. Raw gravity and GPS position solutions were initially filtered to compensate for hardware filtering within the gravity meter. Filtering of remaining high‐frequency noise was accomplished with a spatial, moving average smoother. Due to upward continuation effects imposed by the ice cover, the theoretically estimated minimum resolvable gravity feature size for the Lake Vostok survey is 8 km, consistent with an analysis of power spectra comparing the gravity signal to noise calculated from geographically repeated lines. Comparison of gravity results with subice topography indicates that the gravity data are sensitive to real features including the existence of major crustal structures. Repeated lines and crossovers were analyzed to estimate uncertainties for the Lake Vostok data set, with both of these repeatability measures indicating relative accuracy in the 2 mGal range for the unleveled data and 1 mGal after leveling.

GPS accuracy estimation using map matching techniques: Applied to vehicle positioning and odometer calibration

A test-bed application, called Map Matched GPS (MMGPS) processes raw GPS output data, from RINEX files, or GPS derived coordinates. This developed method uses absolute GPS positioning, map matched, to locate the vehicle on a road centre-line, when GPS is known to be sufficiently accurate. MMGPS software has now been adapted to incorporate positioning based on odometer derived distances (OMMGPS), when GPS positions are not available. Relative GPS positions are used to calibrate the odometer. If a GPS position is detected to be inaccurate, it is not used for positioning, or for calibrating the odometer correction factor. In OMMGPS, GPS pseudorange observations are combined with DTM height information and odometer positions to provide a vehicle position at ‘1 s’ epochs. The described experiment used GPS and odometer observations taken on a London bus on a predefined route in central of London. Therefore, map matching techniques are used to test GPS positioning accuracy, and to identify grossly inaccurate GPS positions. In total, over 15,000 vehicle positions were computed and tested using OMMGPS. In general, the position quality provided by GPS alone was extremely poor, due to multipath effects caused by the urban canyons of central London, so that odometer positioning was used much more often to position the vehicle than GPS. Typically, the ratio is 7:3 odometer positions to GPS positions. In the case of one particular trip, OMMGPS provides a mean error of position of 8.8 m compared with 53.7 m for raw GPS alone.

GPS–GIS‐Based Procedure for Tracking Vehicle Path on Horizontal Alignments

Abstract: This article presents a global positioning system–geographic information system (GPS–GIS)‐based procedure for the deduction of the horizontal alignment of a road based on the path of a control vehicle. Using differential GPS surveying, field data were collected at a 0.1‐second interval, under different speed conditions on a 25‐km section of a two‐lane rural highway in eastern Ontario. The raw GPS data were post‐processed to filter out the possible errors and then imported into a GIS environment for analysis and interpretation of the results. An extension for ArcView was written to determine the geometric features of the highway horizontal alignment, including the tangents, spirals, and circular curves. Values were obtained for the radius and length of nine circular curves, length of spirals, and the lateral position of the vehicle path along the straight and curved segments. These values were compared with the same features of the actual highway alignment. The results showed that the developed procedure and ArcView extension could produce the horizontal alignment of a road quickly, accurately, and for a relatively low cost. In addition to the extraction of the horizontal alignment of a road, the procedure can be used to track the actual vehicle path under normal driving conditions and compare it with the horizontal alignment of a road in an investigation concerning driver behavior.