• Proceedings of the Korean Society of Surveying, Geodesy, Photogrammetry, and Cartography Conference
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• 2003.10a
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• pp.87-90
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• 2003

정밀한 위치결정에 사용되는 GPS는 초기 군사목적을 벗어나 자동차, 선박, 비행기 등의 항법은 물론 측량분야, 지각 및 구조물의 변위 감시, 우주, 통신, 국방 분야 등 매우 광범위한 분야에서 활용되고 있으며, 그 이용도가 급속히 증가하는 추세이다. 그러나 GPS 관측값은 부정오차와 정오차 등 많은 오차를 포함하고 있기 때문에 이를 소거하거나 최소화하여야 한다. GPS 오차는 크게 위성궤도나 위성시간 오차등 위성에 관련된 오차, 수신기 잡음이나 다중경로 등 수신기 관련 오차, 그리고 대류권이나 전리층에 의한 전파 오차로 구분할 수 있다. 이들 오차들은 대부분 차분방법과 수학적 알고리즘에 의해 소거되거나 최소화되지만, 다중경로와 수신기 잡음은 소거하거나 축소할 수 없다. 다중경로는 관측당시의 수신기 주변환경에 따라 바뀌기 때문에 수학적으로 소거할 수 없으며, 수신기 잡음은 수신기 내부의 노이즈로 인하여 발생하기 때문에 소거하기가 상당히 어렵다. 본 연구에서는 다중경로에 의한 GPS 기선변화를 알아보기 위해서 여러 조건하에서 정적 GPS 측량을 실시하였다. 먼저 정확한 좌표를 알고 있는 한 점에 GPS를 설치하고 다른 두 대의 GPS을 임의 점에 설치하였고, 이들 두 GPS 중에 하나의 수신기에 다중경로 환경을 설정하였다 정적 GPS 관측시 기선에 어떠한 변화가 오는 파악하기 위해서 기선처리와 망조정을 통해 기선길이와 좌표값을 산출하였다. 이러한 다중경로 실험은 구조물 모니터링 등 mm 정확도를 요구하는 GPS 측량에 유용하게 사용될 수 있을 것이다.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.36 no.6
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• pp.621-628
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• 2018

More than four visible GPS (Global Positioning System) satellites are required to obtain absolute positioning. However, it is not easy to satisfy this condition when a rover is in such unfavorable condition as an urban area. As a consequence, clock-aided positioning has been used as an alternative method especially when the number of visible satellites is three providing that receive clock error information is available. In this study, LSC (Least-Squares Collocation) method is proposed to interpolate clock errors for clock-aided positioning after analyzing the characteristics of receiver clock errors. Numerical tests are performed by using GPS data collected at one of Korean CORS (Continuously Operating Reference Station) and a nearby GPS station. The receiver clock errors are obtained through the DGPS (Differential GPS) positioning technique and segmentation procedures are applied for efficient interpolation. Then, LSC is applied to predicted clock error at epoch which clock information is not available. The numerical test results are analyzed by examining the differences between the original and interpolated clock errors. The mean and standard deviation of the residuals are 0.24m and 0.49m, respectively. Therefore, it can be concluded that sufficient accuracy can be obtained by using the proposed method in this study.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.26 no.5
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• pp.529-536
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• 2008

Researches about 3-D Positioning system using GPS were carried out many-sided by national organs, laboratories, the worlds of science. And most of researches were development of relative positioning algorithm and its applications. Relative positioning has a merit, which can eliminate error in received signals. But its error increase due to distance of baseline. GPS absolute positioning is a method that decides the position independently by the signals from the GPS satellites which are received by a receiver at a certain position. And it is necessary to correct various kinds of error(clock error, effect of ionosphere and troposphere, multi-path etc.). In this study, results of PPP(Precise Point Positioning) used Bernese GPS software was compared with notified coordinates by the NGII(National Geographic Information Institute) in order to analyze the positional accuracy of permanent GPS sites. And the results were compared with results of AUSPOS - Online GPS Processing Service for comparison with relative positioning.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.3
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• pp.225-231
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• 2011

The satellite clock anomalies, one of the abnormal signal factors of the GPS satellites, can have a significant impact on the GPS measurements. However, it can be difficult to detect the anomalies of the satellites clock before the range of the satellites clock error becomes bigger than the range of the other factors, due to the measurement including error of the orbit, ionosphere delay, troposphere delay, multipath and receiver clock. In order to perform quick and accurate detection by minimization of critical range in anomalies of the satellites clock, this paper suggested a solution to detect precise anomalies of the satellites clock after application of carrier smoothing filter from measurement by dual-frequency and adjustment of errors which can be occurred by other factor and the receiver clock errors. The performance of the proposed method was confirmed by comparing to the satellite clock biases which are provided by IGS.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.3
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• pp.65-70
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• 2005

Incorrect ambiguity integer of GPS make a large error on attitude determination. In this paper one method is suggested for estimating the multipath of GPS carrier measurement while attitude determination. The multi-antenna system consists of 4 antennas have the same clock error help to make attitude determination effectively. If the distance between antennas is a half wavelength, it is not necessary to search the ambiguity integer and the multipath of GPS carrier measurement can be estimated. The results of the simulation are shown and analyzed.

• 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.

• Journal of the Korean Institute of Navigation
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• v.20 no.3
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• pp.73-84
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• 1996

선진국에서의 GPS 위성정보를 활용한 자세결정 센서개발은 새로운 GPS 관련연구 분야로 떠오르고 있는 실정이다. 지금까지 국제학회에 보고된 대부분의 연구는 GPS 위성신호의 Carrier phase 측정을 통해 고중차등을 이용한 방법으로 주로 3-D 자세결정방식에 치중하고 있으나, 아직 실무에서의 활용은 이른 것으로 알려지고 있다. 본 논문은 GPS 위성신호의 범용이 C/A 코드 프로세싱 GPS 수신기 정보를 활용하여 선박의 방위센서 개발에 관한 연구이다. 본 연구에서는 1차적으로 GPS 위성신호의 오차벡터를 진시간으로 측정 및 분석을 통해 GPS 위성오차중 가장 심각한 S/A 오차 발생기간에도 방위센서 구측을 위한 정보획득에는 문제가 되지 않음을 확인하였고, 수신된 Two-Point 위성정보를 이용 새로운 선박의 방위센서 "GPS-Compass"를 구측 비선형 모델하에서의 해상 실험을 통해 본 연구에서 제시한 "GPS-Compass"의 새로운 선박 방위센서로의 활용가능성을 보였다.박 방위센서로의 활용가능성을 보였다.

• Journal of Advanced Navigation Technology
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• v.18 no.5
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• pp.421-428
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• 2014

GPS satellite positions can be obtained from the navigation message transmitted from the GPS satellite. In this paper, the accuracy of broadcast orbit and clock are analyzed by comparing with the NGA precise ephemeris. For analyzing global and local orbit errors in 2004 to 2013, GPS satellite visibilities are calculated in Korea. Local RMS of 3D orbit error and SISRE are 4 cm and 3 cm less than global RMS of 3D orbit errors and SISRE. Orbit and clock errors are calculated for each GPS satellite Block for 10 years. SISRE of Block IIA satellites are 2.8 times greater than Block IIF satellites. The correlation between orbit errors and shadow condition is analyzed. The orbit errors in shadow is 2.1% higher than that in sunlight. Correlation analysis between the orbit errors and solar/geomagnetic index shows that orbit errors has a high correlation with from 2004 to 2008. However, the correlation became low since 2009.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.26 no.4
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• pp.397-405
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• 2008

The position accuracy is primarily dependent on the satellite position and signal delay caused by several elements. To know the effect of the delay on the estimated positions, we simulated GPS raw data (RINEX) with GPS errors using Bernese ver5.0. GPS errors used in this paper are Ionospheric delay, Cycle slip, Troposphere, DOP and Random error. If the baseline is short, the position error according to TEC is not large, since the ionospheric delay effect can be removed by ion-free combination. However, if the baseline is long, 3 dimensional position error up to 10cm is occurred. The 3D position error of coordinates with cycle slip is hardly ever changed up to 60% of cycle slip. Because the simulated cycle slips are equally distributed on satellites, the positioning was not seriously affected by the cycle slip. Also, if percentage of cycle slip is 60%, three dimensional error is sharply increased over 1m. The position error is calculated by using the observation data (2 hours) which was selected by DOP less than 3. And its accuracy is more improved about $3{\sim}4cm$.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.29 no.6
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• pp.677-685
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• 2011

In order to enhance public transportation and to maintain information credibility, improvement of accuracy regarding route and positional information of public transport is very significant. There have been a variety of methods using GPS to measure accuracy of location-based services. However, the researches of evaluation regarding kinematic position of linear objects measured by vehicle/kinematic GPS are still insufficient. That's why our paper aims to suggest method of evaluation accuracy on a real-time bus route surveyed by GPS by SBM(Single Buffering Method). To make it come true, we compared the findings on the static and dynamic positioning by using PP(Point Positioning), DGPS and GPS/INS integrated systems and analyzed the accuracy and error effects among them, focusing on Anyang city. Consequently, we can find out that in case of P.P. comparing positioning accuracy between RTK DGPS and GPS/INS, both of them have survey result within a margin of error of 5m. More importantly, we can evaluate positional accuracy of each GPS system based on the work provision of a public survey such as error for P.P.(14.5m, 18.1m), DGPS(16.9m, 18.5m), and GPS/INS(18.4m, 18.5m). We are expecting that proposed method in our paper can be utilized in a wide range of categories such as feasibility testing of GPS field survey and high accuracy of positioning for Bus Information System.