Download

Results

AHMCT researchers are developing a wireless network-based approach for delivering precision GPS differential correction signals to vehicles. This system enables novel applications requiring decimeter or centimeter-level accuracy, and removes the need for a dedicated RF license. It leverages emerging wireless standards and infrastructure. In addition, the significant remaining bandwidth can support many other applications, such as using vehicles as probes for traffic management.

Download

Abstract

In this paper, the potential of long-range kinematic GPS positioning with a multiple reference station (MRS) network for airborne applications is discussed. A novel method of creating Virtual Reference Stations (VRS) is proposed for post-processed airborne GPS kinematic applications, which is called the modified semi-kinematic VRS method (MS-VRS). The purpose of the VRS is to generate data from real GPS observations made by the MRS network, resembling that of a non-existing (virtual) reference station situated close to the project area, so that the commonly used methods for short-range kinematic GPS data processing can be used to determine the position of the aircraft. During the initial phase, the VRS of the MS-VRS method refers to a fixed position according to the aircraft’s initial approximate position, and the corrections are applied according to the aircraft’s trajectory. The MS-VRS method differs from the conventional VRS method and semi-kinematic VRS method (S-VRS) in that when the aircraft’s current approximate position is more than 10 km from the initial VRS position, a new VRS is created. The MS-VRS data can be generated in RINEX format, so that it can be processed using any kinematic GPS post-processing software. Using a simulated kinematic test with static data, the MS-VRS method showed a 12.1 to 47.6 percent improvement in the three coordinate components with respect to the conventional single reference station (SRS) approach. Tests and analysis with real airborne GPS data are presented in some detail using a MRS network and flight test data in Norway. The results indicate that centimetre-level accuracy can be achieved based on the proposed MS-VRS method, which
is superior to the S-VRS method, with improvements of 11.4 to 47.4 percent in terms of standard deviations of the coordinate domain.

Download

SUMMARY

The paper shortly describes the ultra-rapid orbits of GPS satellites and their potential applications in real-time monitoring of position variations. The processing procedure for near real-time network solution using precise orbits is explained. With the recent accuracy of the ultra-rapid ephemerides using their predictions the network in near real-time with unprecedented reliability can be processed and thus can be used for monitoring of stability of the individual stations or the whole network. These results can be further improved by Kalman filtering approach. The near real-time solution has been tested at Department of Theoretical Geodesy at the Slovak University of Technology. An experiment with a device which allowed performing antenna horizontal displacements with exactly measurable magnitude is discussed in the last chapter of the paper. Our approach enables to detect sub-centimeter displacement in several hours after the event at sites in distances of tens of kilometers from the nearest network station.

Download

Abstract

Real-time high precision GPS surveying and navigation applications have been constrained to 'short range' due to the presence of distance-dependent errors in the betweenreceiver single-differenced observables. Over the past few years, the use of a GPS reference station network, to extend the inter-receiver distances (user-to-reference station), has attracted great interest. This network-based approach can be extended to include GPS/GLONASS receivers. In order to model the distance-dependent errors such as the ionospheric and tropospheric biases, the ambiguities in the GPS/GLONASS reference station network should first be fixed to their correct integer values. However, even with precisely known station coordinates, it is still a challenge to fix the ambiguities in reference station networks, especially when a new satellite rises above the horizon. In this paper two procedures for ambiguity resolution, suitable for real-time implementations, in GPS/GLONASS reference station networks are suggested. The first procedure is single-epoch ambiguity resolution after an ambiguity is initialized. As the distance-dependent errors (atmosphere errors and orbit errors) exhibit a high degree of temporal correlation for short time spans, the double-differenced residuals can be represented as a linear function of time for short periods of up to a few minutes. On an epoch-by-epoch and satellite-by-satellite basis these systematic errors (or biases) can be estimated using previous measurements with fixed ambiguities, and precisely predicted for use in ambiguity resolution during the following measurement epochs. The second procedure is suitable for a newly risen satellite, or after a long data gap. Atmospheric biases also exhibit strong spatial correlations between satellite pairs. The atmospheric delay information derived from other satellites, with fixed ambiguities, can be used in predicting the atmospheric bias for a newly risen satellite, and for those satellites that have unknown ambiguities associated with them. A test data set from a GPS/GLONASS reference station network was used to evaluate the performance of these procedures. The experimental results show that the proposed procedures can reliably and efficiently resolve the integer ambiguities of reference station networks, in real-time, on a single-epoch basis.

Download

Abstract

Regional gravimetric geoid and quasigeoid models are now commonly fitted to GPS-levelling data, which simultaneously absorbs levelling,GPSand quasi/geoid errors due to their inseparability.We propose that independent vertical deflections are used instead, which are not affected by this inseparability problem. The formulation is set out for geoid slopes and changes in slopes. Application to 1,080 astrogeodetic deflections over Australia for the AUSGeoid98 model shows that it is feasible, but the poor quality of the historical astrogeodetic deflections led to some unrealistic values.

Download

Abstract

Over the past 18 months, a team in the Western Australian Centre for Geodesy at Curtin University of Technology, Perth, has been researching the optimum configurations to achieve long-range and precise GPSbased aircraft positioning for subsequent airborne mapping projects. Three parallel strategies have been adopted to solve this problem: virtual reference stations (VRS), precise point positioning (PPP), and multiple reference stations (MRS). This paper briefly summarises the concepts behind the PPP and VRS techniques, describes the development and testing of in-house software, and presents the latest experimental results of our research. Current comparisons of the PPP and VRS techniques with an independently well-controlled aircraft trajectory and ground-based stations in Norway show that each deliver precisions of around 3 cm. However, the implementation of more sophisticated error modelling strategies in the MRS approach is expected to better deliver our project’s objectives.

Download

Abstract

Over the past few years, there has been substantial growth in multiple-reference-station networks used to overcome the limitations of standard real-time kinematic (RTK) systems. SydNET is a project to establish a permanent real-time GPS network in the Sydney basin area providing Network-RTK support to users in the area. SydNET is being developed by NSW Department of Lands in partnership with the School of Surveying & SIS at the University of New South Wales. This paper presents recent developments of the SydNET network. Preliminary test results will be presented which will show the network’s performance, achievable accuracy. It will outline the SydNET system, its operation, current status and vision of future development as a high precision positioning service infrastructure.

Download

Abstract

The Metropolitan Water District (MWD) of Southern California, in collaboration with the Scripps Orbit and Permanent Array Center (SOPAC) at University of California, San Diego, has undertaken the design and implementation of a 30-station real time GPS network (RTN). MWDRTN is currently in the final field installation stage (first phase) and the initial fieldtesting phase. The network is designed for use by MWD surveyors and engineers for construction projects, pipeline locations, mapping, GIS studies and projects, deformation studies (including an existing dam deformation system at Diamond Valley Lake) and various other positional needs within our service area (5200 square miles of Southern California).

MWDRTN utilizes continuous GPS (CGPS) sites that were installed (1995 to 2002) by the Southern California Integrated GPS Network for seismic and crustal motion research and several newly installed (2004) sites from Earthscope’s Plate Boundary Observatory project. Some of the SCIGN stations were previously converted to real-time operations, with the raw 1 Hz data recorded at SOPAC for earthquake monitoring. Each of the approximately 20 CGPS sites chosen for the network (scattered across both Riverside and San Bernardino Counties) are equipped with a wireless LAN (WiLAN) radio, a data buffer and appropriate antenna, cables, etc. The sites communicate with the MWD enterprise communications backbone via the WiLAN radios on an IP-based system. The data are collected at a main server using Geodetics, Inc’s RTD (Real Time Dynamics) software, a server/client application providing users with precise instantaneous network positioning through TCP/IP (cell phone modems).

The primary objective of installing this network is the increase in labor efficiency (and therefore cost savings) that we expect to achieve. MWD has a large workload of projects, undertaken by both employees and contractors. MWD will gain from the ability of both work forces to utilize the RTN for conjoint projects. Productivity should increase by utilizing oneperson crews and by having access to instantaneous turn around for construction projects and emergency repairs. Using RTD’s network-based approach we will also achieve better accuracy and reliability than using a standard RTK-based solution, by allowing users access to instantaneous multiply determined position solutions.

This paper will describe the network design, first phase of installation, and initial results.

Download

Summary

The goal of the interdisciplinary, international meeting called “railway project 2009” was to outline
the requirements needed to progress towards interoperable railway infrastructure data based on absolute
coordinates along European Railway lines.
During the meeting, railway experts examined the requirements from three perspectives: Geodesy,
GIS and the needs of the railway companies. In addition the interest of the track industry and the UIC
were also considered.
This text starts by describing some of the fundamental components in the use of absolute coordinates
in railways:
- The development for track work where absolute coordinate use was initiated (ch. 1);
- a rough overview of the reference data components (ch. 2);
- the potential of generalising the “work process approach” successfully implemented in the
track domain to support the overall “infrastructure work process” (ch. 3).
The paper then focuses on the outcome of the “railway project 2009” meeting (ch 4) and the results of
follow-up discussions (ch. 5), this by taking into account the statement given by the geodesy experts,
that referencing the coordinate data to ETRS89 would allow the railway companies to move towards
full data interoperability at a 1 cm-precision level.
Some personal feed-backs (ch. 6) clearly shows that the subject initiated by the “railway project 2009”
is a potential starting point of an important ongoing work, to be dealt with by the railway companies,
to enhance data interoperability. Ideally it might be accomplished by the interdisciplinary, international
teamwork, involving the experts in direct interaction with the industry and with the railway management.
An outlook on the ongoing technical and organisational subjects to be deepened concludes (ch. 7) the
work done.

Download

Abstract

The establishment and maintenance of geodetic reference frames which are an essential foundation for all surveys related to land management, GIS and large scale mapping are very expensive. Large countries like Brazil cannot afford a dense, nation-wide control network. Active GPS reference stations provide an alternative concept for reference frames. Because of the high potential of relative carrier phase-based GPS measurements, it is sufficient to tie GPS surveys to the next reference station with precisely known coordinates. The connection to adjacent control monuments is not required as long as network distortions can be either neglected or modelled. Therefore the effort for classical monumented networks can be reduced drastically. For those applications requiring sub decimetre or even centimetre-level accuracy in real time, the working radius of a field station is limited to less than 10 km from the next reference station, especially in the equatorial region. To overcome this unsatisfactory situation, the spatial and temporal correlations of GPS measurement errors introduced by ionosphere, troposphere, and satellite orbit need to be modelled in a real time multi station solution. A concept for such a local GPS reference network covering only densely populated areas or an important economic region has been developed in a collaborative Brazilian-German research project. In the paper, we discuss the set up of a local GPS reference network that was operated in the urban area of Recife during November 2000, and positioning results for control and cadastral surveys are given. The real time multi station solutions yield more precise, more reliable, and much faster results, but are still limited by strong ionospheric anomalies.