• Proceedings of the Korean Society of Surveying, Geodesy, Photogrammetry, and Cartography Conference
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• 2007.04a
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• pp.89-92
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• 2007

This investigation aims at calculating the geoid height, distance between the ellipsoidal height and the orthometric height by GPS/Levelling data for nationwide 58 Bench Marks, and calculating the effect of geoid height to engineering public works. The accuracy of the results from baseline analyses and adjustment of a network. using GPS surveying data by nationwide 58 BM show 4mm for horizontal direction and 7cm for vertical direction. The 58 geoid height was calculated by GPS/Levelling. For a construction work field GPS/Levelling for distributed 4 BM in test area can calculate the orthometric height in 20 ppm relativity accuracy with 95% reliability. Besides the calculated geoid height in the investigation was 0.367m higher than EGM96 model. The test results of a engineering work site, the result by EGM96 model was 1.8cm in 10km and it was also 3.6cm in interpolation method. The results show that it is equivalent to levelling of $20mm\sqrt{S}$.

• Journal of Korean Society for Geospatial Information Science
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• v.25 no.2
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• pp.57-65
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• 2017

The purpose of this study is to analyze the feasibility of using Global Navigation Satellite System(GNSS)/Geoid technology in determining orthometric height in mountain. For the study, a test bed was set up in and around Mount Jiri and GNSS surveying were conducted. The orthometric height of 39 benchmarks was determined by applying the EGM2008, KNGeoid13, and KNGeoid14 geoid models and the accuracy was estimated by comparing with the offical Benchmarks orthometric height value issued by National Geographic Information Institute(NGII) and finally, the results were analyzed with the Aerial Photogrammetry Work Regulations. As a result of the study, it was found that the accuracy of the orthometric height determination by GNSS/Geoid technology was ${\pm}7.1cm$ when the KNGeoid14 geoid model was applied. And also, it can be confirmed that it is usable for the less than 1/1000 plotting scales as a vertical reference point for the aerial triangulation in Aerial Photogrammetry.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.31 no.6_2
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• pp.567-576
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• 2013

The determination of the geoid in South Korea is a national imperative for the modernization of height datums, specifically the orthometric height and the dynamic height, that are used to monitor hydrological systems and environments with accuracy and easy revision, if necessary. The geometric heights above a reference ellipsoid, routinely obtained by GPS, lead immediately to vertical control with respect to the geoid for hydrological purposes if the geoid height above the ellipsoid is known accurately. The geoid height is determined from gravimetric data, traditionally ground data, but in recent times also from airborne data. This paper illustrates the basic concepts for combining these two types of data and gives a preliminary performance assessment of either set or their combination for the determination of the geoid in South Korea. It is shown that the most critical aspect of the combination is the gravitational effect of the topographic masses above the geoid, which, if not properly taken into account, introduces a significant bias of about 8 mgal in the gravity anomalies, and which can lead to geoid height bias errors of up to 10 cm. It is further confirmed and concluded that achieving better than 5 cm precision in geoid heights from gravimetry remains a challenge that can be surmounted only with the proper combination of terrestrial and airborne data, thus realizing higher data resolution over most of South Korea than currently available solely from the airborne data.

• Journal of Korean Society for Geospatial Information Science
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• v.23 no.4
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• pp.67-74
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• 2015

GNSS/Leveling technology makes it possible to get geoidal height geometrically using GNSS and Leveling technology. GNSS/Geoid technology refers to a technology for obtaining orthometric height by subtracting geoidal height achieved by Geoid technology from ellipsoidal height achieved by GNSS technology. The purpose of this study is to verify the accuracy of the ellipsoidal height determination in order to verify the accuracy of the orthometric height determination by the GNSS/Geoid technology. For the study, a test bed was selected in Kyungnam province and GNSS Static surveying was accomplished in the test bed and then the GNSS data was processed in accordance with various analysis conditions. So, it was verified the accuracy of the ellipsoidal heights determination in accordance with the surveying conditions under the GNSS Static surveying. According to the research results, to ensure the 3cm goal accuracy of the ellipsoidal height determination, it should be surveyed by four fixed points on the survey area periphery and more than two hours of the GNSS occupation time, And also, it was found that should be limited to a baseline distance of 20km under the GNSS Static surveying.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.13 no.2
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• pp.285-289
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• 1995

This paper describes the determination of geoid using height data measured by GPS and Spirit Levelling. The GPS data of the 88 stations were used to determine the geoid undulation (N) which can be easily obtained by subtracting the orthometric height(H) from the ellipsoidal height(h). From the geoid undulation (N) calculated at each station mentioned above, geoid plots with a contour interval of 0.25 m were drawn using two interpolation methods. The following interpolation methods were applied and compared with each other: Minimum Curvature Method and Least Squares Fitted Plane. Comparison between geometric geoid and gravimetric geoid undulation by FFT technique was carried out.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.29 no.4
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• pp.351-357
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• 2011

In this study, we have intended to analyze the possibility of using the precise geoid model and to find the best geoid model for working by the airborne LiDAR system. So we have calculated the geoid height from the precise geoid models (KGEOID08, EGM2008, EIGEN-CG03C) and have analyzed results by comparing the geometric geoid height from surveying and geoid heights from geoid models. As a result, the KGEOID08 that had 0.152m of RMSE was assessed the best geoid model for making DEM(DTM) by airborne LiDAR system. Also we have found the needed arrangement and numbers of reference point when the KGEOID08 was used for conversion into orthometric height of LiDAR data.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.13 no.2
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• pp.125-133
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• 1995

The geoidal heights of a country may be computed from astrogedetic, gravimetric or satellite data. In this paper, the geoid models to the Bessel ellipsoid(KGM95-A) have been determined by the astrogedetic method, which is surface fitting techniques using deflections of the vertical and geoid height constraints. Transformation equations and the gravimetric geocentric geoid(KGM93-C) were applied to obtain the geoid height referred to the Tokyo Datum of the Korean geodetic network, the comparison of the astrogedetic results and discussions of the geoid information were added.

• Korean Journal of Geomatics
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• v.2 no.1
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• pp.7-15
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• 2002

Recent development of ultra-high and high degree Earth geopotential model opens new avenues to determine the Earth gravity field through spectral techniques to a very high accuracy and resolution. However, due to data availability, quality, and type, the performance of these new EGMs needs to be validated in regional or local scale geoid modeling. For establishing the best reference surface of geoid determination, recent geopotential models are evaluated using GPS/Leveling-derived geometric geoid and the Korean gravimetrical GEOID (KGEOID98) developed by National Geography Institute in 1998. Graphical and statistical comparisons are made for EGM96, GFZ97, PGM2000A and GPM98A models. The mean and standard deviation of difference between geometric height and geoid undulation calculated from GFZ97 are $1.9\pm{46.7}\;cm$. It is shown that the GFZ97 and the GPM98A models are better than the others in the Korean peninsula because the GFZ97 has a smaller bias. It means that the KGEOID98 needs some improvement using the GFZ97 instead of EGM96.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.40 no.4
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• pp.305-313
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• 2022

The evolution of the GNSS (Global Navigation Satellite System) technology has enhanced positioning performance in terms of positioning accuracy and time efficiency. The technology makes it possible to determine orthometric heights at a few centimeter accuracies by transforming accurate ellipsoid heights if an accurate geoid model has been employed. This study aims to generate a correction surface using GNSS/leveling co-points and a local geoid model, Thailand Geoid Model 2017 (TGM2017), through the Kriging interpolation method in a small local area. Combining the surface and TGM2017 significantly improves height transformation with the 1-cm RMSE (Root Mean Square Error) fit of 10 GNSS/leveling reference points and a mean offset of +0.1 cm. The evaluation of the correction surface at 5 GNSS/leveling checkpoints shows the RMSE of 1.0 cm, which is 82.6 percent of accuracy improvements. The GNSS leveling method can possibly be used to replace a conventional leveling technique at a few centimeter uncertainties in the case of small areas with clear-sky and high satellite visibility environments.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.28 no.2
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• pp.217-222
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• 2010

The geoid is the level surface that closely approximates mean sea level and usually used for the origin of vertical datum. For the computation of geoid, various sources of gravity measurements are used in South Korea and, as a consequence, the geoid models may show different results. however, a limited analysis has been performed due to a lack of controlled data, namely the GPS/Leveling data. Therefore, in this study, the gravimetric geoids are compared with the geodetic geoid which is obtained through the GPS/Leveling procedures. The gravimetric geoids are categorized into geoid from airborne gravimetry, geoid from the terrestrial gravimetry, NGII geoid(geoids published by National Geographic Information Institute) and NORI geoid(geoi published by National Oceanographic Research Institute), respectively. For the analysis, the geometric geoid is obtained at each unified national control point and the difference between geodetic and gravimetric geoid is computed. Also, the geoid height data is gridded on a regular $10{\times}10-km$ grid so that the FFT method can be applied to analyze the geoid height differences in frequency domain. The results show that no significant differences in standard deviation are observed when the geoids from the airborne and terrestrial gravimetry are compared with the geomertric geoid while relatively large difference are shown when NGII geoid and NORI geoid are compared with geometric geoid. Also, NGII geoid and NORI geoid are analyzed in frequency domain and the deviations occurs in long-wavelength domain.