• Journal of Korean Society for Geospatial Information Science
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• v.2 no.2 s.4
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• pp.143-151
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• 1994

3-D coordinates that result form GPS survey are not applied directly in korea because they are based on WGS 84 ellipsoid. Thus they must be transformed into longitude, latitude on the Bessel ellipsoid and orthometric height. Transformation parameters must be determined in order to perform the coordinate transformation. Also, coordinate transformation be preformed on longitude, latitude and ellipsoidal height. First estimation of Bessel geoidal height must be accomplished to acquire Bessel ellipsoidal height This paper suggests accuracy of coordinate transformation according to the estimation method of Bessel geoidal height. Also, This paper suggests that Bessel geoidal height have influence on the coordinates transformation.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.13 no.2
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• pp.237-244
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• 1995

In this study, we made WGS84 geoidal height model from GPS measurements for bench marks and calculated geoidal height of B.Ms which were selected check points using the hi-linear, trend surface fitting and triangulation interpolation method. From these, the interpolation accuracy was studied. Also, we tried to study accuracy of height transformation by making up orthometric height with latitude and longitude on Bessel ellipsoid for bench marks which were calculated by applying transformation parameters that were got GPS measurements for precise primary control stations. As a result of this study, the WGS84 geoidal height and orthometric height could be determined as a deviation value of 20 cm.

• Journal of the Korea Institute of Building Construction
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• v.15 no.6
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• pp.631-639
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• 2015

In the unit modular construction, the unit module prefabricated in a factory with a high level of accuracy does not fit completely onto the ground-joint junction due to the low accuracy of the ground work. This difference in the level of accuracy can cause diverse problems, such as twisting the upper unit modules and loosening the connection between the module and the footing. On this background, the aim of this study is to develop a technique for adjusting the height of the prefabricated individual footing. To accomplish the aim, a height adjustment method using bolts and nuts is proposed, and a shop drawing and the construction sequence are also presented in this study. The structural safety is verified through a structure simulation. In the future, research will be conducted on a mock-up test of the height adjustment method developed in this study, and an analysis of economic feasibility will be performed in order to verify its constructability and usability.

• Journal of Korea Multimedia Society
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• v.21 no.8
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• pp.864-875
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• 2018

In this paper, we propose a measurement method for height of white light scanning interferometer using deep learning. In order to measure the fine surface shape, a three-dimensional surface shape measurement technique is required. A typical example is a white light scanning interferometer. In order to calculate the surface shape from the measurement image of the white light scanning interferometer, the height of each pixel must be calculated. In this paper, we propose a neural network for height calculation and use virtual data generation method to train this neural network. The accuracy was measured by inputting 57 actual data to the neural network which had completed the learning. We propose two new functions for accuracy measurement. We have analyzed the cases where there are many errors among the accuracy calculation values, and it is confirmed that there are many errors when there is no interference fringe or outside the learned range. We confirmed that the proposed neural network works correctly in most cases. We expect better results if we improve the way we generate learning data.

• Journal of Wind Energy
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• v.14 no.3
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• pp.25-33
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• 2023

In order to secure the safety of increasing offshore activities such as offshore wind farm maintenance and fishing, IMPACT, a mid-term marine weather forecasting system, was established by predicting marine weather up to 7 days in advance. Forecast data from the Korea Hydrographic and Oceanographic Agency (KHOA), which provides the most reliable marine meteorological service in Korea, was used, but wind speed and wave height forecast errors increased as the leading forecast period increased, so improvement of the accuracy of the model results was needed. The Model Output Statistics (MOS) method, a post-correction method using statistical machine learning, was applied to improve the prediction accuracy of wave height, which is an important factor in forecasting the risk of marine activities. Compared with the observed data, the wave height prediction results by the model before correction for 6 to 7 days ahead showed an RMSE of 0.692 m and R of 0.591, and there was a tendency to underestimate high waves. After correction with the MOS technique, RMSE was 0.554 m and R was 0.732, confirming that accuracy was significantly improved.

• Journal of the Korean Society for Nondestructive Testing
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• v.7 no.2
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• pp.35-41
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• 1988

The optimum test conditions of measuring the crack height were determined for the two-probe ultrasonic diffraction method. The applicability and the accuracy of the two-probe ultrasonic diffraction method on the inclined artificial cracks and the fatigue cracks were evaluated. It us possible to measure the height of the normal and inclined artificial cracks with the maximum error of ${\pm}\;0.5mm$ with the two-probe ultrasonic diffraction method. It was found, however, that the accuracy of this method in meaasuring the height of the fatigue crack depends on the degree of closure of the crack tip. It was desirable to choose a refraction angle as small as possible, but the angle should not be so small that the distortion of the lateral waveform became appreciable.

• Journal of the Korean Society for Precision Engineering
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• v.34 no.2
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• pp.89-94
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• 2017

Micro-screws can be defined by their outer diameter of generally less than 1 mm. They are manufactured by head forging and thread rolling processes. In this study, the thread rolling process was numerically analyzed for a micro-screw with a diameter and pitch of 0.8 and 0.2 mm, respectively. Through finite element (FE) analysis, the effects of two design parameters (die gap and chamfer height) on the dimensional accuracy were investigated. Three combinations of chamfer heights were chosen first and the corresponding die gap candidates selected by geometric calculation. FE analyses were performed for each combination and their results indicated that the concave chamfer height should be less than 0.3 mm, while a 10 ?m difference in the die gap might cause degeneration in dimensional accuracy. These results conclude that ultra-high accuracy is required in die fabrication and assemblies to ensure dimensional accuracy in micro-screw manufacturing.

• Journal of Ocean Engineering and Technology
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• v.35 no.5
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• pp.336-346
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• 2021

The prediction of wave conditions is crucial in the field of marine and ocean engineering. Hence, this study aims to predict the significant wave height through machine learning (ML), a soft computing method. The adopted metocean data, collected from 2012 to 2020, were obtained from the Korea Institute of Ocean Science and Technology. We adopted the feedforward neural network (FNN) and long-short term memory (LSTM) models to predict significant wave height. Input parameters for the input layer were selected by Pearson correlation coefficients. To obtain the optimized hyperparameter, we conducted a sensitivity study on the window size, node, layer, and activation function. Finally, the significant wave height was predicted using the FNN and LSTM models, by varying the three input parameters and three window sizes. Accordingly, FNN (W48) (i.e., FNN with window size 48) and LSTM (W48) (i.e., LSTM with window size 48) were superior outcomes. The most suitable model for predicting the significant wave height was FNN(W48) owing to its accuracy and calculation time. If the metocean data were further accumulated, the accuracy of the ML model would have improved, and it will be beneficial to predict added resistance by waves when conducting a sea trial test.

• Journal of the Architectural Institute of Korea Planning & Design
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• v.36 no.2
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• pp.79-86
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• 2020

In order to accommodate the increase in urban population due to government-led national planning and economic growth, many buildings such as houses and business building were supplied. Although the building law was revised and managed to manage the supplied buildings, for the sake of economic benefit, there have been buildings that are enlarged or reconstructed without declaring building permits. In order to manage these buildings, on-site surveys were conducted. but it has many personnel consumption. To solve this problem, a method of using a satellite image and a manned aircraft is utilized, but it is diseconomical and a renewal cycle is long. In addition, it is not utilized to the height, and although it is judged by the shading of the building, it has limitations that it must be calculated individually. In this study, height of the building was calculated by using the unmanned aerial vehicle with low personnel consumption, and the accuracy was verified by comparison with the building register and measured value. In this study, spatial information was constructed using a fast unmanned aerial vehicle with low manpower consumption and the building height was calculated based on this. The accuracy by comparing the calculated building height with the building register and the actual measurement.

• Journal of the Korean Association of Geographic Information Studies
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• v.25 no.2
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• pp.48-58
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• 2022

This study tried to assess the applicability of a hand-held LiDAR for measuring the geometric structures of forest trees including diameters at a breast height(DBH) and tree height(H). A traditional method using tapelines was conducted to analyze the accuracy of the LiDAR instrument in the Taebaeksan national park in South Korea. Four statistical indices which are bias, root mean square error, mean absolute error, and correlation coefficient were employed to compare the measurements by the LiDAR instrument and traditional method. The DBHs from the LiDAR were very similar to those from the traditional method. And it indicated that the LiDAR is sufficient to be a alternative of a traditional method. However, there was a limitation in assessing the accuracy of LiDAR for measuring tree height by comparing the measurements by observer's eyes since they included different error sources. Further study is needed to assess the accuracy of LiDAR instrument for tree height through more reliable measurements.