• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
• /
• v.36 no.5
• /
• pp.403-412
• /
• 2018

Recently, GNSS (Global Navigation Satellite System)-derived orthometric height determination has been studied to improve the time and cost-effectiveness of traditional leveling surveying. However, the accuracy of this new survey method was evaluated when unknown points are located lower than control points. In this study, the accuracy of GNSS-derived orthometric height was examined using TPs (Triangulation Points) to verify the stability of surveying in mountainous areas. The GNSS survey data were obtained from Mungyeong, Unbong/Hadong, Uljin, and Jangseong. Three unknown points were surrounded by more than three UCPs (Unified Control Points) or BMs (Benchmarks) following the guideline for applying GNSS-derived orthometric height determination. A newly developed national geoid model, KNGeoid17 (Korean National Geoid 2017), has been applied for determining the orthometric height. In comparison with the official orthometric heights of the TPs, the heights of the unknown points in Mungyeong and Unbong/Hadong differ by more than 20 cm. On the other hand, TPs in Uljin and Jangseong show 15-16 cm of local bias with respect to the official products. Since the precision of official orthometric heights of TPs is known to be about 10 cm, these errors exceed the limit of the precision. Therefore, the official products should be checked to offer more reliable results to surveyors. As an alternative method of verifying accuracy, three different GNSS post-processing software were applied, and the results from each software were compared. The results showed that the differences in the whole test areas did not exceed 5 cm. Therefore, it was concluded that the precision of the GNSS-derived orthometric height was less than 5 cm, even though the unknown points were higher than the control points.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
• /
• v.36 no.1
• /
• pp.1-8
• /
• 2018

To compensate for the shortcomings of spirit leveling, research on the determination of GNSS (Global Navigation Satellite System)-derived orthometric height has been actively carried out. However, most analyses were primarily performed inland. In this study, the influences of the arrangement of control points, observation duration, and geoid model on the accuracy of the GNSS-derived orthometric height have been analyzed to suggest the proper method to apply the determination of GNSS-derived orthometric height to the leveling loop disconnected area. As a result, it was found that two known points located near the unknown points need to be fixed in the leveling loop disconnected area. Further, 3 cm level of accuracy can be achieved if the GNSS survey is performed over two days, for four hours per day. In terms of the geoid model, the latest national geoid model should be applied rather than the EGM08 (Earth Gravitational Model 2008) to minimize regional bias and increase accuracy. Future research is necessary to apply the determination of the GNSS-derived orthometric height technique as a method to connect with the islands because the vertical reference system used inland and that used for the islands in Korea are still different.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
• /
• v.32 no.5
• /
• pp.527-537
• /
• 2014

In 2013, NGII(National Geographic Information Institute) has developed and provided the KNGeoid13(Korean National Geoid Model 2013) to support the fundamental computation of GNSS-derived orthometric height. In this study, the adjusted ellipsoidal height, the sum of geoidal height and height by the leveling, is applied to calculate the GNSS-derived orthometric height without the local bias, based on GNSS static surveying and KNGeoid13. The mean of errors in GNSS-derived orthometric heights could be verified with the leveling data, which was actually less than 0.5 cm with using the adjusted ellipsoidal heights, but 3 cm by calculating differences between ellipsoidal heights and geoidal heights. By analyze the accuracy of GNSS-derived orthometric height depending on the duration of observation, we could realized 95% of data shows less than 4 cm accuracy, when the GNSS survey conducting for 4 hours spread over two days, but while the case of GNSS survey conducting for 4 hours and 2 hours respectively, resulted in 95% of data less than 5cm level of accuracy. Also, if the ambiguity is fixed, less than 10cm of accuracy could be obtained at 95% of data for only 30 minutes GNSS survey over a day. Following the study, we expected that the height determination by GNSS and geoid models can be used in the public benchmark surveying.