• Journal of the Korean Association of Geographic Information Studies
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• v.12 no.1
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• pp.36-43
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• 2009

In this study, the impact of the covariance between the baselines on the network-based GPS positioning is analyzed. For the analysis, the multi-baseline solutions with properly modeled covariance between the baselines and the combined solutions from the single-baseline solutions are obtained, respectively. Then, the accuracies of both solutions are evaluated in terms of coordinate residuals, i.e., the differences between the positioning solutions and the published stations' coordinates. The results indicate that the positioning accuracy in static mode depends much on the geometry of GPS satellites rather than the proper modeling of covariance between the baselines. Also, slight but negligible improvement in positioning accuracy is observed in static solutions. Therefore, one may use combined solutions as an alternative to multi-baseline solutions for the network-based GPS positioning. However, multi-baseline solution with properly modeled covariance between the baselines is recommended to use especially for the applications to detect very small displacement, i.e., deformation of the building or bridge.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.36 no.4
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• pp.245-254
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• 2018

Impact of tropospheric correction techniques on accuracy of the GPS (Global Positioning System) derived ellipsoidal heights has been experimentally assessed in this paper. To this end, 247 baselines were constructed from a total of 88 CORS (Continuously Operating Reference Stations) in Korea. The GPS measurements for seven days, acquired from the so-called integrated GNSS (Global Navigation Satellite Systems) data center via internet connection, have been processed by two baseline processing software packages with an application of the empirical models, such as Hopfield, modified Hopfield and Saastamoinen, and the estimation techniques based on the DD (Double-Differenced) measurements and the PPP (Precise Point Positioning) technique; hence a total number of the baseline processed and tested was 8,645. Accuracy and precision of the estimated heights from the various correction schemes were analyzed about baseline lengths and height differences of the testing baselines. Details of these results are summarized with a view to hopefully providing an overall guideline of a suitable selection of the modeling scheme with respect to processing conditions, such as the baseline length and the height differences.

• Proceedings of the Korean Society of Surveying, Geodesy, Photogrammetry, and Cartography Conference
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• 2004.04a
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• pp.97-102
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• 2004

현재 4차원 정밀측정이 가능한 GPS는 데이터 처리와 사용기기 면에서 많은 발전을 이루고 있으며, 정밀한 데이터 결과를 제공하고 있다. 처리 방식에 따른 기선거리별 한계치에 대한 재검증을 실시하고자 하였으며, 측지용 GPS 수신기를 이용한 기선측정에 있어, L$_1$주파수 수신 GPS 시스템의 유효측정거리에 대하여 논하였다. 또한 일반적인 기선처리방식 이외의 다양한 처리기법들을 적용하여 각 단ㆍ중ㆍ장기선에 대해 가장 알맞은 처리방식을 도출하려고 하였으며 결과를 도출하는 과정에서 GPS 상대거리 관측데이터에 대해 양호한 데이터를 선별할 수 있는 기준 안을 마련하고자 하였다.

• 한국지형공간정보학회:학술대회논문집
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• 2002.03a
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• pp.9-16
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• 2002

본 연구에서는 광주를 고정으로 전라남도 4점과 전라북도 5점으로 삼각망을 구성하고 각 측점에서 관측한 데이터를 방송력과 정밀력을 이용하여 기선 해석을 실시하고 기선거리별 궤도력의 영향을 통계학적으로 비교 분석하여 전라남북도에 이르는 GPS관측망의 궤도력에 따른 각 기선별 오차분포를 정량화 할 수 있었고, 정밀력을 이용한 기선해석은 기준 공분산 값이 모두 1 미만으로 나타나 두 지역간의 지역적 변환계수와 지구중심절대좌표를 선정함에 있어 과대오차를 현저히 줄일 수 있었다.

• Journal of Korean Society for Geospatial Information Science
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• v.10 no.2 s.20
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• pp.57-66
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• 2002

This paper establised GPS network consist of 75km average baseline lengths over Jeollanamdo and Jeollabukdo nine point station and fixed Gwangju point station. We quantitavely analyzed how much precision of the baseline determination is improved for GPS survey when using the precise eqhemeris instead of tile broadcast ephemeris of GPS satellites. The observed data for each baseline were processed two times with the same conditions alternately changing the broadcast and the precise ephemeris. The standard deviations from the repeated measurments for each baseline ara compared between the results of using the broadcast ephemeris and the precise ephemeris. As the results, the precision, stability and reliability of the baseline determination using the precise ephemeris is better than those of using the broadcast ephemeris for all baselines.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.26 no.2
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• pp.157-164
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• 2008

GPS baseline analysis is a mathematical procedure which estimates a baseline vector from carrier-phase double-differenced observations. Least squares technique is generally applied for the processing and integer ambiguities in the observations should be resolved to obtain maximum accuracy of the solution. In GPS control surveying, after assembling the baseline solutions into a network, adjustment is performed to derive final coordinate sets of unknown points. This paper deals with details of GPS baseline analysis for the $2^{nd}$ order national geodetic network adjustment. After reviewing GPS campaigns carried out by National Geographic Information Institute (NGII) and their observations. technical issues and considerations for the GPS baseline analysis are presented with emphasis of selecting the processing strategies and software. Finally, the analyzed results will be evaluated by examining the close of figures formed by joining the processed baseline vectors.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.4
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• pp.593-602
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• 2018

This study examined the impact of trivial baselines obtained from GNSS single-baseline processing into a network adjustment in terms of accuracy and estimated coordinates sets. To this end, depending on the inclusion of the dependent baselines, three different types of experimental GNSS networks were composed and adjusted. The results showed that the networks including the trivial baselines are generally overestimated, but differences in the derived coordinates are limited at the millimeter level. A comparison of the adjusted coordinates with those published by the national geodetic agency showed that results of the network consisting of only the independent baselines are more constant than those of the networks with trivial baselines. Finally, a trivial baseline should be excluded from the GNSS network adjustment with a consideration of the realistic accuracy presentation and data processing burden.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.14 no.2
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• pp.199-207
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• 1996

According to the different baseline lengths, we quantitatively analyzed how much precision of the baseline de-termination is improved for GPS survey when using the precise ephemeris instead of the broadcast ephemeris of GPS satellites. For this research, we selected seven baselines ranging from 15 km to 201 km and performed GPS measurements more than six times for each baseline. The observed data for each baseline were processed two times with the same conditions alternately changing the broadcast and the precise ephemeris. The standard deviations from the repeated measurements for each baseline are compared between the results of using the broadcast ephemeris and the precise ephemeris. As the result, the precision, stability and reliability of the base-line determination using the precise ephemeris is better than those of using the broadcast ephemeris for all base-lines. When using precise ephemeris for the baselines longer than 65 km, the precision less than 0.1ppm is always obtained and the precision improvement rate by using the precise ephemeris is considerably greater than that for the shorter baselines. We expect that this result might be a quantative basis for the decision about what ephemeris is better for the baseline length and the demanded precision in GPS survey.

• 한국지구물리탐사학회:학술대회논문집
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• 2008.10a
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• pp.155-165
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• 2008

A method to determine the azimuth of a baseline by using the measured apparent directions of the Sun, the measurement time and the latitude and the longitude of the survey point. Comparing the azimuths determined by this method and those determined by the PDGPS(Post Processed Differential GPS) on 3 different baselines, the differences (this method - PDGPS) between the azimuths determined by two methods were -13", +45" and +24" respectively. This method can be used as an effective and rapid tool in cases that require the accuracy lower than 1 arc-min.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.22 no.4
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• pp.411-418
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• 2004

This paper is the study about a method for determining the azimuth of a baseline by measuring the apparent direction of the Sun. It is simple to realize this method, as it requires, in addition to the apparent direction of the Sun already measured, the observation time and the latitude and the longitude of the survey point. Comparing the azimuths determined by this method and those determined by the PDGPS(Post Processed Differential GPS) on 3 different baselines, the differences(PDGPS - this method) between the azimuths determined by two methods were -13", +45" and +24" respectively. It can be an effective and rapid tool in cases that require the accuracy lower than 1 arc-min.than 1 arc-min.