• Journal of Korean Society for Geospatial Information Science
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• v.4 no.2 s.8
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• pp.79-90
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• 1996

It is well known that point positioning using a C/A-code receiver is severely biased by errors in pseudorange. This paper shows the procedures of quantitive analysis for several error elements and that some methods to monitor SA(selective availability) of witch process is not opened are proposed. It is possible to verify the effects of SA in the Doppler shift and receiver clock drift variation. Easy methods to reduce SA effects are to fit second order polynomials for the one and a linear function for the other. With periodic autocorrelation functions. SA effects are analyzed and first order Gauss-Markov process parameters are decided.

• Journal of Institute of Control, Robotics and Systems
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• v.8 no.5
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• pp.425-433
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• 2002

After the removal of SA (Selective Availability), horizontal accuracy of 25m(2dRMS) is easily obtained using GPS (Global Positioning System). In this paper, the error characteristics without SA are analyzed and a navigation algorithm concerns this error characteristics is proposed to further improve the accuracy. The proposed method utilizes the relationship between elevation angle and errors that are remained after ionospheric and troposheric delay compensation. The relationship is derived from real measurements and used as a weighting matrix of weighted least squares estimator. Furthermore, a RAIM (Receiver Autonomous Integrity Monitoring) technique is included to remove abnormal measurements affected by multi-path or low SNR (Signal-to-Noise Ratio). It is shown that using the proposed method, more than 4 times accurate result, which is comparable with DGPS (Differential GPS), can be obtained from experiments with real data. Besides accuracy and reliability, the proposed method reduces large jumps in position and maintains better performance than a method using mask angle to completely remove satellites below this mask angle. Thus it is expected that the proposed method can be efficiently applied to land navigation where some satellites are blocked by building or forest.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.19 no.1
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• pp.1-8
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• 2001

The aim of this study is to know the GPS absolute positioning accuracy after discontinuing of Selective Availability (SA). The GPS satellite clock errors and the observation station coordinates were calculated using GPS C/A code pseudorange and compared with the JPL precise ephemerides and the previous known coordinates. As the results, the correction or the GPS clock errors in SA-on is about $\pm$40m but in SA-off $\pm$2m. The 95% probable errors for the measurements in SA-on are about $\pm$65m but in SA-off $\pm$10m in X, Y and SA-off $\pm$15m in Z.

• Proceedings of the Korean Society of Surveying, Geodesy, Photogrammetry, and Cartography Conference
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• 2003.04a
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• pp.433-441
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• 2003

최근 SA(Selective Availability)의 해제에 따른 GPS의 활용이 증대되면서 차량운행에 있어서도 저가 GPS 수신기의 활용이 활발하게 이루어지고 있으며, 일반 차량 운행자를 위한 상용화가 급속도로 이루어지고 있다. 하지만 저가 GPS수신기를 통한 실시간 위치정보의 제공은 실질적으로 상당한 오차를 포함하고 있다. 이는 저가 수신기가 가지고 있는 문제라 할 수 있다. 이에 본 연구에서는 저가 수신기와 정밀 측위용 이주파 수신기를 이용하여 측지분야에서 검증된 GPS측량방법을 통해 오차를 비교ㆍ분석하고 저가 수신기의 정확도 향상을 위한 방법을 제시하고자 하였다.

• Journal of Korean Society for Geospatial Information Science
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• v.8 no.1 s.15
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• pp.73-84
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• 2000

Map matching technique is an essential part of the car navigation and other related positioning fields such as dead reckoning and GPS data logging upon the GIS database. This paper is to break down map matching techniques, to categorize them, and to propose a simple technique for GPS based map matching technique. For categorization of techniques, two approaches have been adopted. One is to only use geometric information, and the other is to use both geometric and topological information. Some pros and cons of each method have been described. In addition, a simple map matching technique, set forth in this paper, has been introduced for properly utilizing the advantage of GPS points after the absence of the chronic problem of selective availability, which had been prevailed recently. Some research opportunities and problems of the technique have also been discussed.

• Journal of Korean Society for Geospatial Information Science
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• v.12 no.1 s.28
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• pp.11-20
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• 2004

The purpose of this paper is to evaluate the applicability of GPS data for real-time traffic information collection especially after SA removal. Two major results have been reported. One is the GPS data availability and/or useful data point density for travel time estimation using Circle-X algorithm. 87.23% of data points can be mobilized after SA whereas only 29.94% of data was useful in calculating travel time. The other is the possible reduction of the buffer size that is used for screening the points of all GPS into useful and useless data, respectively. With these outcomes, it is safely expected that the regular GPS alone can provide the data points for real-time travel time estimation instead of the more expensive DGPS system.

• Spatial Information Research
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• v.13 no.3 s.34
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• pp.283-296
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• 2005

Nowadays, Global Navigation Satellite System(GNSS) which is the new concept of positioning system has been developed because of satisfaction human's intelligent desire and rapid science development. GNSS which is represented by GPS provides 3-Dimension positioning information not expensively in whenever, wherever. The industry of positioning information has extending civil market widely as well as military market. So GNSS is running the role of society infra structure including car and airborne navigation, civil engineering, GIS resource, telematics and LBS, and so on. As USA removes the SA(Selective Availability), GPS has monopolizing the market and other countries have been depended on GPS, absolutely. In this paper, the author developed the software for analysis of influence using next generation, Galileo system. The local analysis was performed according to positioning mode. And GPS/Galileo combined system can implement positioning in the worst mask environment like urban cannon.

• Journal of the Korean Geophysical Society
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• v.10 no.1
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• pp.37-44
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• 2007

Nowadays, Global Navigation Satellite System(GNSS) which is the new concept of positioning system has been developed because of satisfaction human's intelligent desire and rapid science development. GNSS which is represented by GPS provides 3-Dimension positioning information not expensively in whenever, wherever. The industry of positioning information has extending civil market widely as well as military market. So GNSS is running the role of society infra structure including car and airborne navigation, civil engineering, GIS resource, telematics and LBS, and so on. As USA removes the SA(Selective Availability), GPS has monopolizing the market and other countries have been depended on GPS, absolutely. In this paper, the author developed the software for analysis of influence using next generation, Galileo system. The local analysis was performed according to positioning mode. And GPS/Galileo combined system can implement positioning in the worst mask environment like urban cannon.

• 제어로봇시스템학회:학술대회논문집
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• 2001.10a
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• pp.56.4-56
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• 2001

Using GPS in the navigation systems such as aviation, maritime and land applications, integrity is considered importantly with accuracy for safety. Integrity monitoring performed in the GPS receiver itself is Receiver Autonomous Integrity Monitoring (RAIM) and need not an independent ground monitoring station. RAIM algorithm uses redundant information when more than four satellites are visible and makes consistency checks between measurement information to alarm users whether the system is operating out of its specified performance limits. Selective Availability (SA) that was used to protect the security interests of the U.S. and its allies by globally denying the full accuracy of the civil system was turned off on May 1, 2000 ...

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.30 no.4
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• pp.413-422
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• 2012

After development of GPS in the 1960's, the United States released SA(Selective Availability) in 2000 and then the GPS has become commercialized to the present. The result of repeatedly developed GPS observation, the GPS real-time observation methods is RTK which basically always needs two base stations and has a fault of the accuracy decreasing as the distance between a mobile station and a receiver is increasing. Because of these weakness, VRS method has come out. VRS(Virtual Reference Station) generates the imaginary point near mobile station from several observatory datum of GPS, sets the accurate location of mobile station, thus shows high reliability and mobility. Now, the cadastral datum point is used with azimuth, repetition, and graphical traversing method for traverse network. The result of measurement indicates many problems because of different accomplishment interval given point, restrictions on the length of the conductor, many errors on the observations. So, this study did comparative analysis of the cadastral datum points through VRS method by Continuously Operating Reference Station. Through the above comparative analysis, The comparative result between surveyed result with repetition method through total station observed Cadastral Control Points and surveyed result with VRS-RTK has shown that average error of x-axis is -0.08m, average error of y-axis, +0.07m and average distance error is +0.11m.