• 한국측량학회지
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• 제38권4호
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• pp.305-315
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• 2020

본 연구는 사진측량, 컴퓨터 비전, 로보틱스 등의 분야에서 사용되는 외부표정요소를 결정하는 단사진의 후방교회법의 알고리즘을 비교하는 것이 목적이다. 이를 위해 항공사진 및 근거리 사진측량에서 사용되고 있는 카메라를 기준으로 지형을 시뮬레이션하여 실험 데이터를 생성하여 알고리즘을 비교하였다. 거의 수직으로 촬영되는 항공사진측량용 카메라에 대한 실험을 통해서 3개의 지상기준점으로도 외부표정요소를 결정할 수 있었으나 프로쿠르스테스 알고리즘은 지상기준점 배치에 민감하였다. 카메라의 자세각이 크게 변하는 근거리 사진측량용 카메라를 대상으로한 실험에서도 프로쿠르스테스 알고리즘의 지상기준점 배치에 민감하였으며 모든 알고리즘이 적어도 6개의 지상기준점이 필요하였다. 두 종류의 카메라를 대상으로 한 실험을 통해서 코사인법칙 기반의 후방교회법은 반복회수가 짧고 명시적인 초기값이 필요하지 않기 때문에 전통적인 사진측량 알고리즘과 유사한 성능을 나타내는 것을 알 수 있었다.

• 한국초등수학교육학회지
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• 제17권1호
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• pp.129-142
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• 2013

이 연구의 목적은 2007년부터 2011년까지 일본수학교육학회에서 발행하는 초등수학교육에 관한 학술지 '산수교육'을 통하여 학술지의 구성, 게재된 초등수학 관련 논문의 개요를 파악하여 정통적 초등수학교육 학술지인 한국초등수학교육학회지에 시사점을 주기 위함이다.

• Journal of Astronomy and Space Sciences
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• 제26권1호
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• pp.31-46
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• 2009

An Unscented Kalman Filter (UKF) for estimation of the attitude and rate of a spacecraft using only magnetometer vector measurement is developed. The attitude dynamics used in the estimation is the nonlinear Euler's rotational equation which is augmented with the quaternion kinematics to construct a process model. The filter is designed for small satellite in low Earth orbit, so the disturbance torques include gravity-gradient torque, magnetic disturbance torque, and aerodynamic drag torque. The magnetometer measurements are simulated based on time-varying position of the spacecraft. The filter has been tested not only in the standby mode but also in the detumbling mode. Two types of actuators have been modeled and applied in the simulation. The PD controller is used for the two types of actuators (reaction wheels and thrusters) to detumble the spacecraft. The estimation error converged to within 5 deg for attitude and 0.1 deg/s for rate respectively when the two types of actuators were used. A joint state parameter estimation has been tested and the effect of the process noise covariance on the parameter estimation has been indicated. Also, Monte-Carlo simulations have been performed to test the capability of the filter to converge with the initial conditions sampled from a uniform distribution. Finally, the UKF performance has been compared to that of the EKF and it demonstrates that UKF slightly outperforms EKF. The developed algorithm can be applied to any type of small satellites that are actuated by magnetic torquers, reaction wheels or thrusters with a capability of magnetometer vector measurements for attitude and rate estimation.

• 한국CDE학회논문집
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• 제22권1호
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• pp.89-99
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• 2017

In order to make a virtual endoscopy system effective for exploring the interior of the 3D model of a human organ, it is necessary to generate an accurate navigation path located inside the 3D model and to obtain consistent camera position and pose estimation along the path. In this paper, we propose an approach to virtual navigation of blood vessels, which makes proper use of orthogonal contours and skeleton curves. The approach generates the orthogonal contours and the skeleton curves from the 3D mesh model and its voxel model, all of which represent the blood vessels. For a navigation zone specified by two nodes on the skeleton curves, it computes the shortest path between the two nodes, estimates the positions and poses of a virtual camera at the nodes in the navigation zone, and interpolates the positions and poses to make the camera move smoothly along the path. In addition to keyboard and mouse input, intuitive hand gestures determined by the Leap Motion SDK are used as user interface for virtual navigation of the blood vessels. The proposed approach provides easy and accurate means for the user to examine the interior of 3D blood vessels without any collisions between the camera and their surface. With a simple user study, we present illustrative examples of applying the approach to 3D mesh models of various blood vessels in order to show its quality and usefulness.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2003년도 Proceedings of ACRS 2003 ISRS
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• pp.1197-1199
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• 2003

ROCSAT-2 mission is to daily image over Taiwan and the surrounding area for disaster monitoring, land use, and ocean surveillance during the 5-year mission lifetime. The satellite will be launched in December 2003 into its mission orbit, which is selected as a 14 rev/day repetitive Sun-synchronous orbit descending over (120 deg E, 24 deg N) and 9:45 a.m. over the equator with the minimum eccentricity. National Space Program Office (NSPO) is developing a ROCSAT-2 Image Processing System (IPS), which aims to provide real-time high quality image data for ROCSAT-2 mission. A simulated ROCSAT-2 image, based on Level 1B QuickBird Data, is generated for IPS verification. The test image is comprised of one panchromatic data and four multispectral data. The qualification process consists of four procedures: (a) QuickBird image processing, (b) generation of simulated ROCSAT-2 image in Generic Raw Level Data (GERALD) format, (c) ROCSAT-2 image processing, and (d) geometric error analysis. QuickBird standard photogrammetric parameters of a camera that models the imaging and optical system is used to calculate the latitude and longitude of each line and sample. The backward (inverse model) approach is applied to find the relationship between geodetic coordinate system (latitude, longitude) and image coordinate system (line, sample). The bilinear resampling method is used to generate the test image. Ground control points are used to evaluate the error for data processing. The data processing contains various coordinate system transformations using attitude quaternion and orbit elements. Through the qualification test process, it is verified that the IPS is capable of handling high-resolution image data with the accuracy of Level 2 processing within 500 m.

• 예술인문사회 융합 멀티미디어 논문지
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• 제7권1호
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• pp.177-186
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• 2017

최근 무인자동차가 큰 관심을 받고 있다. 세계 최대 규모의 온라인 쇼핑 서비스업체인 아마존은 드론을 활용한 배송시스템을 개발하고 있다. 이러한 플랫폼의 항법을 위해서는 정확한 자세정보가 필요하다. 본 논문에서는 저가형 관성센서를 활용한 AHRS 구조 설계를 제안하였다. 쿼터니언기반의 운동방정식, 바이어스가 제거된 자이로 측정치, MEMS 가속도계와 지자기 센서를 이용하여 자세를 추정하는 칼만 filter를 설계하였다. MEMS 자이로의 바이어스를 제거하기 위하여 자이로 측정치와 자세 추정치를 이용하는 자이로 바이어스 제거용 칼만 filter를 추가하였다. 구현한 AHRS의 성능을 고가의 상용 Microstrain사의 3DM-GX3-25 AHRS와 비교 실험을 통하여 칼만 filter가 자이로의 바이어스 오차를 0.0001[deg/s]이하로 추정함을 볼 수 있었다. 또한 최종적으로 구해진 자세에서 롤각과 피치각은 0.2, 0.3[deg]이내의 오차를 보여주었다. 요 각은 6[deg] 이하의 오차가 발생하였다.

• 한국측량학회지
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• 제38권3호
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• pp.175-185
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• 2020

3차원 등록은 서로 다른 좌표계를 갖거나 좌표계가 없는 데이터를 기준 좌표계로 일치시키는 과정으로 사진측량의 절대표정, 정밀도로지도 제작을 위한 데이터 결합 등 다양한 분야에서 사용되고 있다. 3차원 등록은 점을 이용하는 방법과 선형을 이용하는 방법으로 구분이 된다. 점을 이용할 경우 서로 다른 공간해상도를 갖는 경우 동일한 공액점을 찾기 어려운 문제가 있다. 이에 반해 선형을 이용할 경우 공간해상도가 다른 경우 뿐만 아니라 점군 형태의 데이터에서 시작점과 끝점이 같지 않은 공액의 선형을 이용하여 3차원 등록이 가능한 장점이 있다. 본 연구에서는 선형을 이용하여 3차원 등록을 수행하기 위해서 쿼터니언을 이용하여 두 데이터 간의 3차원 회전각을 결정한 후 축척과 3차원 이동량을 결정하는 방법을 제안하였다. 제안한 방법의 검증을 위해 실내에서 구축한 선형과 실외 환경의 지상 모바일매핑시스템을 통해 취득한 선형을 이용하여 3차원 등록을 각각 수행하였다. 실험결과, 실내 데이터를 이용한 경우 축척을 고정한 경우와 고정하지 않은 경우 평균제곱근오차는 각각 0.001054m와 0.000936m로 나타났다. 실외 데이터를 이용하여 500m 구간에서 3차원 변환을 수행한 결과 6개의 선형을 이용하였을 경우 평균 제곱근오차는 0.09412m로 나타났으며 정밀도로지도 제작을 위한 정확도를 만족하는 것을 알 수 있었다. 또한, 선형의 개수를 변화시킨 실험에서 9개 이상의 선형을 이용할 경우도 평균제곱근오차의 변화가 크지 않은 것을 통해 높은 정확도의 3차원 변환을 위해 9개의 선형으로도 충분한 것을 알 수 있었다.

• International Journal of Aeronautical and Space Sciences
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• 제8권1호
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• pp.10-20
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• 2007

For spacecraft attitude control, reaction wheel (RW) steering laws with more than three wheels for three-axis attitude control can be derived by using a control allocation (CA) approach.1-2 The CA technique deals with a problem of distributing a given control demand to available sets of actuators.3-4 There are many references for CA with applications to aerospace systems. For spacecraft, the control torque command for three body-fixed reference frames can be constructed by a combination of multiple wheels, usually four-wheel pyramid sets. Multi-wheel configurations can be exploited to satisfy a body-axis control torque requirement while satisfying objectives such as minimum control energy.1-2 In general, the reaction wheel steering laws determine required torque command for each wheel in the form of matrix pseudo-inverse. In general, the attitude control command is generated in the form of a feedback control. The spacecraft body angular rate measured by gyros is used to estimate angular displacement also.⁵ Combination of the body angular rate and attitude parameters such as quaternion and MRPs(Modified Rodrigues Parameters) is typically used in synthesizing the control command which should be produced by RWs.¹ The attitude sensor signals are usually corrupted by noise; gyros tend to contain errors such as drift and random noise. The attitude determination system can estimate such errors, and provide best true signals for feedback control.⁶ Even if the attitude determination system, for instance, sophisticated algorithm such as the EKF(Extended Kalman Filter) algorithm⁶, can eliminate the errors efficiently, it is quite probable that the control command still contains noise sources. The noise and/or other high frequency components in the control command would cause the wheel speed to change in an undesirable manner. The closed-loop system, governed by the feedback control law, is also directly affected by the noise due to imperfect sensor characteristics. The noise components in the sensor signal should be mitigated so that the control command is isolated from the noise effect. This can be done by adding a filter to the sensor output or preventing rapid change in the control command. Dynamic control allocation(DCA), recently studied by Härkegård, is to distribute the control command in the sense of dynamics⁴: the allocation is made over a certain time interval, not a fixed time instant. The dynamic behavior of the control command is taken into account in the course of distributing the control command. Not only the control command requirement, but also variation of the control command over a sampling interval is included in the performance criterion to be optimized. The result is a control command in the form of a finite difference equation over the given time interval.⁴ It results in a filter dynamics by taking the previous control command into account for the synthesis of current control command. Stability of the proposed dynamic control allocation (CA) approach was proved to ensure the control command is bounded at the steady-state. In this study, we extended the results presented in Ref. 4 by adding a two-step dynamic CA term in deriving the control allocation law. Also, the strict equality constraint, between the virtual and actual control inputs, is relaxed in order to construct control command with a smooth profile. The proposed DCA technique is applied to a spacecraft attitude control problem. The sensor noise and/or irregular signals, which are existent in most of spacecraft attitude sensors, can be handled effectively by the proposed approach.