• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.19 no.2
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• pp.155-161
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• 2001

When determining a three dimensional position for engineering purposes, we can use the GPS survey to find position. According to the enhancement of precision for domestic Geoid model, the positional accuracy of GPS about precise method of vertical position has been also increased. But by considering Geoid undulation, it is difficult to measure GPS-derived elevations. Because Geoid undulation has changed little in local sites, GPS-derived elevations are similar to orthometric height. By ignoring Geoid undulation, it is possible to measure GLT-derived elevations at the local. small construction sites. GLT(GPS Leveling Technique) provides a method for computing orthometric heights. GLT processes the data more rapidly than conventional measurement devices. We only considered the weight factors affecting accuracy between the points. That is, the GPS procedures to produce satisfactory elevation accuracy depends on the method of observations, receivers and conditions of the local environment. A comparison was performed between the GPS survey using Geoid model and GLT at a part within Pusan National University and construction model sites in South Korea. And the writers proved the GPS surveying is efficient in positioning accuracy, time, and cost on a construction sites.

• 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.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 Korea Contents Association Conference
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• 2007.11a
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• pp.942-946
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• 2007

The new gravity field combination models are expected to improve the knowledge of the Earth's global gravity field. This study evaluates six global gravity field models derived from gravimetry and altimetry surface data in a comparison with ground truth in South Korea. For calculating a more accurate estimate of the geoid heights from the height anomalies, the terrain corrections due to the terrain masses over geoid have considered, the model for the topographic correction is a spherical harmonic expansion of the ETOPO2 DTM model. Geoid heights obtained from GPS and levelling in land area of South Korea are compared with those from the EGMs. The results show that EIGEN-CG03C EGM and EIGEN-GL04C EGM displayed the nearest results to GPS/leveling, and also confirmed the importance of terrain correction for geoid height in case of the uneven topography.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.12 no.1
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• pp.69-76
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• 1994

In this paper, the characteristics of coordinate transformation between the WGS84 and the Bessel ellipsoids according to the assumed values of the geoidal height on Bessel ellipsoid at the geodetic datum origin of Korea were investigated. For this, based on GPS data of 11 control points in Chungnam and Chungbuk province, the mean shift values between ellipsoids were calculated in each case. The geoidal heights on the Bessel ellipsoid were modelled in the area and the coordinate transformation coefficients were derived, and then the accuracy of the transformed coordinates according to fluctuations in geoidal heights were studied.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.14 no.1
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• pp.49-58
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• 1996

This paper deals with the gravimetric solution of geoid by Fast Fourier Transform(FFT) technique in and around Korean Peninsula. The used reference surface is OSU91A geopotential model up to degree and order 180 refered to GRS80. The remove and restore technique was applied to obtain the geoidal height in this paper. And the FFT with 20% window was applied to compute the medium wavelength effect from terrestrial gravity anomalies. For the comparison of computed results, the geometric geoidal height was derived from GPS/Levelling data. According to the comparison, the mean value and RMSE of the differences are 0.3819m and 0.4695m respectively.

• Journal of Positioning, Navigation, and Timing
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• v.5 no.4
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• pp.221-233
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• 2016

This paper deals with performance assessment of the kinematic network-based GPS positioning technique with a view to using it for ellipsoidally referenced bathymetric surveys. To this end, two field trials were carried out on a land vehicle and a surveying vessel. Single-frequency GPS data acquired from these tests were processed by an in-house software which equips the network modeling algorithm with instantaneous ambiguity resolution procedure. The results reveals that ambiguity success rate based on the network model is mostly higher than 99.0%, which is superior to that of the single-baseline model. In addition, achievable accuracy of the technique was accessed at ${\pm}1.6cm$ and 2.7 cm with 95% confidence level in horizontal and vertical component respectively. From bathymetric survey at the West Nakdong River in Busan, Korea, 3-D coordinates of 2,011 points on its bed were computed by using GPS-derived coordinates, attitude, measured depth and geoid undulation. Note that their vertical coordinates are aligned to the geoid, the so-called orthometric height which is widely adopted in river engineering. Bathymetry was constructed by interpolating the coordinate set, and some discussion on its benefit was given at the end.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.18 no.4
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• pp.359-367
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• 2000

This paper suggests that coefficients models of the Earth's gravitational potential can be used to calculate height anomalies which are then reduced to the geoid undulation to determine more precise geoid undulation. The potential coefficients and modified coefficients of EGM96 and KODEM33 digital elevation model in and around the Korean peninsula were used for this study. The magnitude of height anomaly computed in this study reached 0.025 m and the mean vaule showed -0.015 m. In this study, geometrical geoid undulation was derived from GPS/Leveling data for evaluating the precisely computed geoid undulation. In comparison with geometric and gravimetric geoid undulations, mean value and standard deviation of the differences showed 0.0114 m and 0.2817 m respectively and it showed the improvement of results.

• Journal of Navigation and Port Research
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• v.37 no.5
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• pp.463-469
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• 2013

This paper focuses on GPS positioning accuracy variations according to locations of obstacles which surround GPS station. We derived precise coordinates of a GPS station which has a good visibility. Its observation data was rewritten by assuming signal blocking due to obstacle in the elevation angle of $10^{\circ}$ to $70^{\circ}$. We processed daily and hourly data for 10 days. In the results using daily data, RMSE was at 10mm level. And RMSE increased to 100mm levels in case of hourly data. As the elevation angle of obstacle increased, the horizontal and vertical RMSE increased, while the height estimates decreased. These results showed the higher the elevation angle of the obstacle increased the loss of large amounts of data by blocking satellite signals direction. In terms of the direction, when the blocking thing was located in the east or west, the coordinate has larger error in the east-west direction. And if signal was blocked at the south direction, the difference between the east-west error and the south-north position error was reduced.

• Proceedings of the KSRS Conference
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• 2004.10a
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• pp.344-346
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• 2004

IKONOS 1m satellite imagery is particularly well suited for 3-D feature extraction and 1 :5,000 scale topographic mapping. Because the image line and sample calculated by given RPCs have the error of more than 11m, in order to be able to perform feature extraction and topographic mapping, rational polynomial coefficients(RPCs) camera model that are derived from the very complex IKONOS sensor model to describe the object-image geometry must be refined by several Ground Control Points(GCPs). This paper presents a quantitative evaluation of the geometric accuracy that can be achieved with IKONOS imagery by refining the offset and scaling factors of RPCs using several GCPs. If only two GCPs are available, the offsets and scale factors of image line and sample are updated. If we have more than three GCPs, four parameters of the offsets and scale factors of image line and sample are refined first, and then six parameters of the offsets and scale factors of latitude, longitude and height are updated. The stereo images acquired by IKONOS satellite are tested using six ground points. First, the RPCs model was refined using 2 GCPs and 4 check points acquired by GPS. The results from IKONOS stereo images are reported and these show that the RMSE of check point acquired from left images and right are 1.021m and 1.447m. And then we update the RPCs model using 4 GCPs and 2 check points. The RMSE of geometric accuracy is 0.621 m in left image and 0.816m in right image.