• Journal of Astronomy and Space Sciences
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• v.24 no.3
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• pp.235-248
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• 2007

We developed a software for simulations and analyses of the Image Navigation and Registration (INR) system, and compares the characteristics of Image Motion Compensation (IMC) algorithms for the INR system. According to the orbit errors and attitude errors, the capabilities of the image distortions are analyzed. The distortions of images can be compensated by GOES IMC algorithm and Modified IMC (MIMC) algorithm. The capabilities of each IMC algorithm are confirmed based on compensated images. The MIMC yields better results than GOES IMC although both the algorithms well compensate distorted images. The results of this research can be used as valuable asset to design of INR system for the Communication, Ocean, Meteorological Satellite (COMS).

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.3
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• pp.243-248
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• 2010

This study addresses spacecraft moment of inertial estimation approach using Modified Rodrigues Parameters(MRP). The MRP offer advantage by avoiding singularity in Kalman Filter design for attitude determination caused by the norm constraint of quaternion parameters. Meanwhile, MRP may suffer singularity for large angular displacement, so that we designed appropriate reference attitude motion for accurate estimation. The proposed approach is expected to provide stable error covariance update with accurate spacecraft mass property estimation results.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.6
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• pp.463-472
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• 2017

Inertial Navigation System Alignment is the process to determine direction cosine matrix which is the transformation matrix between the INS body frame and navigation frame. INS initial position value is necessary to INS attitude calculation, so that user should wait until he get such value to start the INS alignment. To remove the waiting time, we propose an alignment algorithm that immediately starts after the INS power on by using pseudo initial position input and then is completed with attitude error compensation by entering true position later. We analyse effect of INS sensor error on attitude in process of time and verify the performance and usefulness of the close-loop alignment algorithm which corrects attitude error from the change of initial position.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.11
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• pp.48-56
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• 2005

Predictive filter theory proposed recently can be characterized by inherent advantages of estimating modelling error and overcoming the disadvantage of the Kalman filter theory. A one-step ahead error is minimized to produce optimized filter performance in the form of the predictive filter. The main advantage of this filter lies in the ability to estimate both state vector and system model error. In this paper, attitude estimation results based upon the predictive filter theory is addressed. Mathematical formulation for estimating bias signal is peformed by using the predictive filter theory, and attitude estimation based upon vector observation is presented. From the results of this study, the potential applicability of the predictive filter is highlighted.

• Journal of Space Technology and Applications
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• v.4 no.3
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• pp.232-243
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• 2024

In order to perform various missions in space, including planetary exploration, estimating the position of a satellite in orbit is a very important factor because it is directly related to the success rate of mission performance. As a study for autonomous satellite navigation, this study estimated the satellite's attitude and real time orbital position using a star sensor algorithm with two star trackers and earth sensor. To implement the star sensor algorithm, a simulator was constructed and the position error of the satellite estimated through the technique presented in the paper was analyzed. Due to lens distortion and errors in the center point finding algorithm, the average attitude estimation error was at the level of 2.6 rad in the roll direction. And the position error was confirmed by attitude error, so average error in altitude direction was 516 m. It is expected that the proposed satellite attitude and position estimation technique will contribute to analyzing star sensor performance and improving position estimation accuracy.

• Aerospace Engineering and Technology
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• v.4 no.1
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• pp.114-121
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• 2005

다목적실용위성 2호 영상의 geo-location 정밀도 80 m (CE90) 요구사항을 만족시키기 위하여, 1개의 IRU 와 2개의 star tracker 들로부터 획득되는 데이터를 이용하여 지상에서 후처리 추정 과정을 거쳐 위성의 자세를 결정하는 정밀자세결정 시스템이 개발되었다. 정밀자세결정 시스템의 정밀도를 극대화하기 위해서는 우주 공간의 극심한 열적 환경으로 인해 발생하는 star tracker 정렬 오차를 효율적으로 보정하여야 한다. 정밀한 정렬 오차의 보정을 위해서는 영상 내에 촬영된 지상의 ground control point 데이터를 이용하여야 하는데, 현실적으로 한반도 모든 지역에 대해 ground control point 를 확보할 수 없다. 현재 항공우주연구원이 확보하고 있거나 이후 확보할 예정에 있는 고해상도 영상을 위한 ground control point 들은 대전지역에 국한될 예정이다. 이와 같은 상황에서 정밀자세결정 시스템의 성능을 높이기 위한 최적의 시스템 운용 개념을 본 연구에서 제시하였으며, 시뮬레이션을 통해 그 타당성을 분석하였다.

• The Korean Journal of Nuclear Medicine Technology
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• v.16 no.1
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• pp.91-95
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• 2012

Purpose: In this study, we evaluated the ejection fraction (EF) according to the difference of patient position in Gated Blood Pool (GBP) scan. Material and Methods: The analysis was performed to 80 patients ($51.2{\pm}17.4$ years old) who examined GBP scan in Department of nuclear medicine, National Cancer Center from March 2011 to August 2011. We divided the patients into two groups; one group received conventional position (raise left arm up supine) and supine position (group 1) and the other group received conventional position and left arm back down supine position (group 2). To observe the change EF according to patient position difference, the image was reconstructed and analyzed by Xeleris (GE, USA). We measured body mass index (BMI) of patients. Result: In group 1, EF error less than 3% occurred at a rate of 72.5% (29 of the 40 patients). In group 2, EF error less than 3% occurred at a rate of 79% (32 of the 40 patients). The patient's BMI did not affect ejection fraction. Conclusion: The EF error of left arm back down supine position closer to conventional position than in supine position shows the results.

• Journal of the Korean Society of Marine Environment & Safety
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• v.19 no.6
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• pp.666-673
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• 2013

This paper proposes the performance evaluation test of attitude heading reference system (AHRS) suitable for small high speed autonomous underwater vehicle(AUV). Although IMU can provides the detail attitude information, it is sometime not suitable for small AUV with short operation time in view of price and the electrical power consumption. One of alternative for tactical grade IMU is the AHRS based micro-machined electro mechanical system(MEMS) which can overcome many problems that have inhibited the adoption of inertial system for small AUV such as cost and power consumption. A cost effective and small size AHRS which incorporates measurements from 3-axis MEMS gyroscopes, accelerometers, and 3-axis magnetometers has been developed to provide a complete attitude solution for AUV and the attitude calculation algorithm is derived based the coordinate transform equation and Kalman filter. The developed AHRS was validated through various performance tests as like the magnetometer calibration, operating experiments using land mobile vehicle and flight motion simulator (FMS). The test of magnetometer calibration shows the developed MEMS AHRS is robust to the external magent field change and the test with land vehicle proves the leveling error of developed MEMS AHRS is below $0.5^{\circ}/hr$. The results of FMS test shows the fact that AHRS provides the measurement with $0.5^{\circ}/hr$ error during 5 minutes operation time. These results of performance evaluation tests showed that the developed AHRS provides attitude information which error of roll and pitch are below $1^{\circ}$ and the error of yaw is below $5^{\circ}$ and satisfies the required specification. It is expected that developed AHRS can provide the precise attitude measurement under sea trial with real AUV.

• Progress in Medical Physics
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• v.14 no.3
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• pp.196-202
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• 2003

In 3-dimensional conformal radiation therapy (3D-CRT) and intensity-modulated radiation therapy (IMRT), many studies on reducing setup error have been conducted in order to focus the irradiation on the tumors while sparing normal tissues as much as possible. As one of these efforts, we developed an image enhancement and registration tool for simulators and portal images that analyze setup errors in a quantitative manner. For setup verification, we used simulator (films and EC-L films (Kodak, USA) as portal images. In addition, digital-captured images during simulation, and digitally-reconstructed radiographs (DRR) can be used as reference images in the software, which is coded using IDL5.4 (Research Systems Inc., USA). To improve the poor contrast of portal images, histogram-equalization, and adaptive histogram equalization, CLAHE (contrast limited adaptive histogram equalization) was implemented in the software. For image registration between simulator and portal images, contours drawn on the simulator image were transferred into the portal image, and then aligned onto the same anatomical structures on the portal image. In conclusion, applying CLAHE considerably improved the contrast of portal images and also enabled the analysis of setup errors in a quantitative manner.

• Proceedings of the Korea Information Processing Society Conference
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• 2019.05a
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• pp.625-628
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• 2019

양돈 업계에서 돼지의 무게는 생산성 측면에서 매우 중요한 요인 중 하나이다. 탑뷰 카메라를 통해 획득된 이미지에서 돼지의 무게를 추정할 때 오차가 적고 신뢰도 있는 결과를 보이기 위해, 오차의 주요 원인인 돼지의 머리를 제거하여야 한다. 우선, 돼지의 머리를 제거하기 위해서는 귀를 탐지하여야 한다. 그러나 돼지의 자세가 바르지 못한 경우 겹침으로 인해 돼지의 귀와 머리가 구분되지 않는 경우가 발생하고, 귀 탐지 과정에서 고려해야 할 변수가 많아지므로 연산량과 수행 시간이 증가한다. 따라서 돼지의 무게 추정을 위해서 돼지의 머리를 제거할 때 돼지의 자세 판정은 필수적이다. 본 논문에서는 돼지의 중점으로부터 돼지의 경계선을 연결한 선분의 길이를 비교하여 돼지의 자세를 빠르게 결정하였다. 이를 통해 자세가 바른 돼지의 머리를 제거하여 돼지의 무게를 측정하는 방법을 제안한다. 실험 결과, 7.8 ms의 수행 시간과 0.97 이상의 정확도로 돼지머리 제거를 위한 자세를 결정할 수 있음을 확인하였다.