• Computational Structural Engineering
• /
• v.11 no.1
• /
• pp.90-95
• /
• 1998

본 고에서는 비압축성 점성유체의 유한요소해석 기법을 소개하였다. 대류항의 상류화 기법으로 안정된 해를 도출할 수 있으며 Penalty 방법에 기반하여 압력항을 지배방정식으로부터 소거함으로써 해석시간과 요구저장공간을 감소시켰다. 실린더 주변의 유동장을 해석하여 와의 방출을 성공적으로 묘사하였으며 항력계수를 17%정도의 오차로 계산하였다. 적응적 요소세분화 기법에 대한 연구를 통해 적절한 오차평가 기법 및 최적의 체눈을 형성하는 기법을 제시하였다. 또한 동적 해석에 적합한 요소재결합 알고리즘에 대한 연구가 진행중이다. 본 고의 결과는 직접적으로 풍공학분야에 사용하기에는 아직 계산 시간의 효율성이나 해의 정확도 및 안정성면에서 무리가 있으나 추가적인 연구를 통하여 해석기법의 개선을 도모하고 컴퓨터 등 계산장비의 급속한 발전으로 장래에 경쟁력을 획득할 수 있을 것으로 기대된다.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.36 no.1
• /
• pp.39-47
• /
• 2008

Automatic landing performance of UAV can be enhanced by adding Pseudolite(PL) to GPS. However, it is very hard to install and operate PL with confidence because GPS satellites are moving and the landing zone are usually changeable. The coverage and accuracy of combined GPS and PL can be estimated by using simulator and the correct information is very crucial to UAV operation. In this paper, design, implementation and evaluation of GPS/PL simulator for UAV landing are given. A very realistic coverage estimation is obtained using GIS data and ray launching method with considerations of the transmitter power level, altitude of UAV, number and location of PL. The expected accuracy is estimated using DOP and NSP computed using both GPS and PL. The performance of simulator is evaluated by comparing with the results of a real GPS receiver, and the certified simulator shows the required accuracy for UAV landing can be easily met by proper installation of at least 2 PLs.

• Journal of the Korean Association of Geographic Information Studies
• /
• v.21 no.2
• /
• pp.24-33
• /
• 2018

DSM and orthoimage, which are representative results of UAV photogrammetry, are high-quality spatial information data and are widely used in various fields of spatial information industry in recent years. However, the UAV photogrammetry has a problem that the quality of the output of the UAV deteriorates due to the altitude of the UAV, the camera calibration, the weather conditions at the time of shooting, the performance of the GPS / IMU and the number of the ground reference points. The purpose of this study is to analyze the location accuracy of unmanned aerial photogrammetry according to the change of the number if ground control points. Experiments were made with fixed wing, and the shooting altitude was set at 130m and 260m. The number of ground reference points used was 9, 8, 5, and 4, respectively. Ten checkpoints were used. XY RMSE for orthoimage and Z RMSE for DSM were compared and analyzed. In addition, the resolution of the orthoimage was determined to affect the judgment of the operator in the verification of the planimetric position accuracy, and the visual resolution was analyzed using the Siemens star target. As a result of the analysis, the variation of the vertical position accuracy is larger than the variation of the planimetric position accuracy when the number of the ground reference points are different. Also The higher the flying height, the greater the effect of change of ground control points on position accuracy.

• Journal of Advanced Navigation Technology
• /
• v.25 no.6
• /
• pp.576-581
• /
• 2021

Compared to a low concentration, a high concentration clearly entails limitations in terms of predictive performance owing to differences in its frequency and environment of occurrence. To resolve this problem, in this study, an artificial intelligence neural network algorithm was used to classify low and high concentrations; furthermore, two prediction models trained using the characteristics of the classified concentration types were used for prediction. To this end, we constructed training datasets using weather and air pollutant data collected over a decade in the Cheonan region. We designed a DNN-based classification model to classify low and high concentrations; further, we designed low- and high-concentration prediction models to reflect characteristics by concentration type based on the low and high concentrations classified through the classification model. According to the results of the performance assessment of the prediction model by concentration type, the low- and high-concentration prediction accuracies were 90.38% and 96.37%, respectively.

• Journal of the Korean Association of Geographic Information Studies
• /
• v.19 no.1
• /
• pp.154-166
• /
• 2016

This study aims to contribute to better understanding the effects of the changes in the parameter values of GroundFilter algorithm(GF), which performs filtering process, and of GridsurfaceCreate algorithm(GC), which creates regular grid, provided in Fusion software on the accuracy of elevation of the final LiDAR-DEM products through comparative analysis. In order to test whether there are significant effects on the accuracy of the final LiDAR-DEM products due to the changes of GF(1, 3, 5, 7, 9) parameter levels and GC(1, 3, 5, 7, 9) parameter levels, two-way ANOVA is conducted based on residuals. The residuals are calculated using the differences between each sample plot's paired field-measured and DEM-derived elevation values given each individual GF and GC level. After that, Tukey HSD test is conducted as a post hoc test for grouping the levels. As a result of two-way ANOVA test, it is found that the change in the GF levels significantly affects the accuracy of LiDAR-DEM elevations(F-value : 27.340, p < 0.01), while the change in the GC levels does not significantly affect the accuracy of LiDAR-DEM elevations(F-value : 0.457). It is also found that the interaction effect between GF and GC levels is not likely to exist(F-value : 0.247). From the results of the Tukey HSD test in the GF levels, GF levels can be divided into two groups('7', '5', '9', '3' vs '1') by the differences of means of residuals. Given the current conditions, LiDAR-DEM can achieve the best accuracy when the level '7' and '3' are given as GF and GC level, respectively.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
• /
• v.33 no.1
• /
• pp.11-21
• /
• 2015

An Ortho-image is the production of removed geometrical displacement, which is generated the aerial image distortion and the relief displacement, etc., using the DSM (Digital Surface Model). Accordingly, the resolution of raw image and the accuracy of DSM will has significant impacts on the ortho-image accuracy. Since the latest DMCII250 aerial camera delivers the high resolution images with five centimeters Ground Sampling Distance(GSD), it expects to generate the high density point clouds and the high quality ortho-images. Therefore, this research has planned for reviewing the potentiality and accuracy of high quality ortho-image production. Following to proceed the research, DSM has been produced through the high density point cloud extracted from DMCII250 aerial image to supply of high density DSM by creation of ortho-image. The research results has been identified that images with the DSM brought out higher degrees in positional accuracy and quality of ortho-image, compared with the ortho-image, produced from the existing digital terrain map or DSM data.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
• /
• v.35 no.6
• /
• pp.535-544
• /
• 2017

UAVs (Unmanned Aerial Vehicle) are generally classified into fixed-wing and rotary-wing type, and both have very different flight characteristics each other during photographing. These can greatly effect on the quality of images and their productions. In this paper, the change of the camera rotation angle at the moment of photographing was compared and analyzed by calculating orientation angles of each image taken by both types of payload. Study materials were acquired at an altitude of 130m and 260m with fixed-wing, and at an altitude of 130m with rotary-wing UAV over an agricultural land. In addition, an accuracy comparison of boundary surveying methods between UAV photogrammetry and terrestrial cadastral surveying was conducted in two parcels of the study area. The study results are summarized as follows. The differences at rotation angles of images acquired with between two types of UAVs at the same flight height of 130m were significantly very large. On the other hand, the distance errors of parcel boundary surveying were not significant between them, but almost the same, about within ${\pm}0.075m$ in RMSE (Root Mean Square Error). The accuracy of boundary surveying with a fixed-wing UAV at 260m altitude was quite variable, $0.099{\sim}0.136m$ in RMSE. In addition, the error of area extracted from UAV-orthoimages was less than 0.2% compared with the results of the cadastral survey in the same two parcels used for the boundary surveying, In conclusion, UAV photogrammetry can be highly utilized in the field of cadastral surveying.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2005.05b
• /
• pp.562-566
• /
• 2005

본 연구에서는 레이더 자료의 수문학적 적용성에 대한 정확도를 개선하고자 기상현업에서 운영하고 있는 관악산 도플러 레이더 자료를 활용하여 POD(Probability of Detection) 분석을 통해 레이더 오자료를 제거하고, 편차 보정기법을 적용하여 레이더 추정강수의 정확도를 개선시켜 이들의 수문학적 적용성을 검토하였다. 이를 위해 다양한 관측 고도각 별로 POD 분석을 수행한 결과 낮은 확률의 POD($p_l$)와 높은 확률의 POD($p_h $)의 범위가 변화하고, 레이더로부터 약 150 km 이상 떨어진 지역에서는 $1.95^{\circ}$ 이상의 고도각에서 탐지한 레이더 에코가 강수 추정에 유용하지 않음을 알 수 있었다. 또한 소양강유역을 대상으로 관측 강우량보다 과소추정되는 Marshall-Palmer 관계식의 레이더 추정강수를 편차 보정기법으로 실시간으로 보정하여 그 정확도를 향상시켰다. 보정된 레이더 추정강수를 HEC-1에 적용하여 유량해석을 수행한 결과, 보정된 레이더 추정 강수를 이용한 모의치와 관측유량사이에 매우 높은 상관성을 보이고 있음을 알 수 있었다. 따라서 편차 보정기법을 통해 보정된 레이더 강수는 수문학적 분석을 위한 입력자료로 유용하게 사용될 수 있을 것으로 판단된다.

• Proceedings of the Korea Information Processing Society Conference
• /
• 2016.10a
• /
• pp.123-124
• /
• 2016

본 연구는 스마트폰 사용자가 응급상황에 처했을 때 사용자의 정확한 위치 정보를 응급 구조 센터에 전달할 수 있는 방법을 개발함에 목적을 둔다. 사고의 경우 실외 뿐만 아니라 실내에서 많은 사고가 발생하는데, 일반적으로 위치 정보를 획득에 사용되는 GPS 의 경우는 실내 위치를 정확하게 파악하기 어렵기 때문에 구조를 지연시키는 문제를 야기한다. 본 연구는 이러한 상황들을 방지하기 위해 GPS와 와이파이, 블루투스를 각각 이용한 삼각 측량법을 통해 실내의 위치정보를 측정하고 더 나아가 압력센서를 통해 사용자의 위치를 3차원적으로도 탐색한다. 실험 결과, GPS를 이용하는 것보다 블루투스를 이용하는 것이 더 정확한 실내 정보를 탐색하는 것을 알 수 있었다. 또한 압력계를 통해 고도를 측정함으로써 건물 내부에서 사용자의 수직적 위치를 측정할 수 있었다. 이러한 결과는 위도 경도의 정확한 정보와 함께 고도에 대한 예측을 가능하게 함으로써 보다 정확한 실내 위치 정보를 획득하여 골든 타임을 확보하는데 도움이 될 것으로 보인다.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.40 no.1
• /
• pp.165-170
• /
• 2015

The topic of this paper is the advanced absolute altitude determination for 3-D positioning using barometric altimeter and the reference station. Barometric altimeter does not provide absolute altitude because atmosphere pressure always varies over the time and geographical location. Also, since Global Navigation Satellites system such as GPS, GLONASS has geometric error, the altitude information is not available. It is the reason why we suggested the new method to improve the altitude accuracy. This paper shows 3-D positioning algorithm using absolute altitude determination method and evaluates the algorithm by real field tests. We used an accurate altitude from RTK system in Seoul as a reference data and acquired the differential value of pressure data between a reference station and a mobile station equipped in low cost barometric altimeter. In addition, the performance and advantage of the proposed method was evaluated by 3-D experiment analysis of PNS and CNS. We expect that the proposed method can expand 2-D positioning system 3-D position determination system simply and this 3-D position determination technique can be very useful for the workers in the field of fire-fighting and construction.