• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1989년도 춘계학술대회
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• pp.51-54
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• 1989

지난 몇년동안 생체에서의 MR 스펙트로 스코피(Mangetic Resonance Spectroscopy)를 위하여 ISIS, VSE, SPARS, STEAM 등과 같은 여러 체적 선택의 방법이 연구되어 왔다. 그러나 이들 3차윈 체적 선택의 방법은 여러 RF 펄스를 사용하여야 되었으며 상대적으로 오랜시간 동안의 RF여기시간(Radio frequency excitation time) 때문에 T1과 T2 감소효과의 영향을 크게 받았다. 본 논문에서는 3차원의 체적을 선택하기 위하여 단일 RF펄스의 사용을 제안하고 있는데, 이 방법은 원통형 체적을 선택하기 위한 방사형 경사 코일 (a radial gradient coil) 방법과 진동자계 (oscillating selection gradient) 방법을 결합하고 있다. 이렇게 하므로 단일 RF 펄스만을 사용하여 체적 선택 시간을 최소화하여 여러 RF 펄스를 사용할 경우 발생하는 파생적인 에코 신호(echo signal)를 피할 수 있었다. 제안된 방법에 의한 실험적 연구결과로서 펜톰(phantom)에 대하여 선택된 체적에 대한 영상과 스펙트럼 (spectrum)을 제시하였다.

• Journal of Positioning, Navigation, and Timing
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• 제5권3호
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• pp.137-144
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• 2016

In this paper, the performance of ranging measurement, which is generated using two receiver clock offsets in one receiver, was analyzed. A spoofer transmits a counterfeited spoofing signal which is similar to the GPS signal with hostile purposes, so the same tracking technique can be applied to the spoofing signal. The multi-correlator can generate two receiver clock offsets in one receiver. The difference between these two clock offsets consists of the path length from the spoofer to the receiver and the delay of spoofer system. Thus, in this paper, the ranging measurement was evaluated by the spoofer localization performance based on the time-of-arrival (TOA) technique. The results of simulation and real-world experiments show that the position and the system clock offset of the spoofer could be estimated successfully.

• 로봇학회논문지
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• 제9권3호
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• pp.154-159
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• 2014

The Global Positioning System (GPS) is widely used to aid the navigation of aerial vehicles. However, the GPS cannot be used indoors, so alternative navigation methods are needed to be developed for micro aerial vehicles (MAVs) flying in GPS-denied environments. In this paper, a real-time three-dimensional (3-D) indoor navigation system and closed-loop control of a quad-rotor aerial vehicle equipped with an inertial measurement unit (IMU) and a low-cost light detection and ranging (LIDAR) is presented. In order to estimate the pose of the vehicle equipped with the two-dimensional LIDAR, an octree-based grid map and Monte-Carlo Localization (MCL) are adopted. The navigation results using the MCL are then evaluated by making a comparison with a motion capture system. Finally, the results are used for closed-loop control in order to validate its positioning accuracy during procedures for stable hovering and waypoint-following.

• 한국음향학회지
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• 제23권1호
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• pp.30-39
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• 2004

본 연구는 3차원 공간상에 있어서의 음상정위를 제어하기 위한 디지털 신호처리 기술, 특히, 음상의 거리정위에 있어서의 머리전달함수 (HRTF)의 역할에 착안한 신호처리 기술을 확립하기 위한 것을 목적으로 한다. 이러한 목적을 달성하기 위하여 본 논문에서는 청각에 있어서의 거리 지각을 제어하기 위한 중요한 요소를 밝혀내기 위해 기존의 Hirsch-Tahara 모델과 음향적 시차 모델에 대해서 청각 실험을 행했다. 그 결과 이 두 모델에 있어서는 음상의 거리지각을 설명하기에는 한계와 전 방향에 있어서는 적용할 수 없는 문제점이 있었다. 이러한 문제점들을 고려해 본 논문에서는 음향적 시차 모델을 전 방향에 있어서 적용 가능하도록 확장된 음향적 시차 모델을 제안해 그 유효성에 대해 청취 실험을 통해 고찰했다. 그 결과, 본 논문에서 제안한 확장된 음향적 시차 모델을 이용하면 수평면 상의 전 방향에 있어서 약 2m 까지의 범위 내에서는 실제 음원에서 지각할수 있는 거리와 거의 같은 수준으로 음상의 거리를 제어함으로써 본 모델의 유효성을 인간을 대상으로한 청취실험을 통해 증명했다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제16권6호
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• pp.2044-2059
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• 2022

Recent works have shown that the geometric constraint can be harnessed to boost the performance of CNN-based camera localization. However, the existing strategies are limited to imposing image-level constraint between pose pairs, which is weak and coarse-gained. In this paper, we introduce a pixel-level epipolar geometry constraint to vanilla localization framework without the ground-truth 3D information. Dubbed EpiLoc, our method establishes the geometric relationship between pixels in different images by utilizing the epipolar geometry thus forcing the network to regress more accurate poses. We also propose a variant called EpiSingle to cope with non-sequential training images, which can construct the epipolar geometry constraint based on a single image in a self-supervised manner. Extensive experiments on the public indoor 7Scenes and outdoor RobotCar datasets show that the proposed pixel-level constraint is valuable, and helps our EpiLoc achieve state-of-the-art results in the end-to-end camera localization task.

• 한국생산제조학회지
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• 제22권3호
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• pp.452-458
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• 2013

Over the past several years, many studies have been carried out in the field of 3D data inspection systems. Several attempts have been made to improve the quality of manufactured parts. The introduction of laser sensors for inspection has made it possible to acquire data at a remarkably high speed. In this paper, a robust inspection technique for detecting defects in 3D pressed parts using laser-scanned data is proposed. Point cloud data are segmented for the extraction of features. These segmented features are used for shape matching during the localization process. An iterative closest point (ICP) algorithm is used for the localization of the scanned model and CAD model. To achieve a higher accuracy rate, the ICP algorithm is modified and then used for matching. To enhance the speed of the matching process, aKd-tree algorithm is used. Then, the deviation of the scanned points from the CAD model is computed.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2002년도 ICCAS
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• pp.79.4-79
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• 2002

Our goal is the development of a system that estimates the location of interested point in a room with accuracy and low cost. Non-contacting position estimating method is widely used in various areas. Among these methods, acoustic signal-based method is the cheapest and provides reasonably accurate estimation as a result of many research efforts. Most of the acoustic-signal-based three-dimensional location estimators such as 3D sonic digitizer are using the ultrasound, and are organized with two procedures; time-of-flight (TOF) estimation and localization estimation. Since the errors in estimating the TOF could be accumulated with that of localization estimate, accuracy of TOF estimate is as...

• Radiation Oncology Journal
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• 제37권4호
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• pp.259-264
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• 2019

Purpose: Accurate localization of the lumpectomy cavity during accelerated partial breast radiation (APBR) is essential for daily setup to ensure the prescribed dose encompasses the target and avoids unnecessary irradiation to surrounding normal tissues. Three-dimensional ultrasound (3D-US) allows direct visualization of the lumpectomy cavity without additional radiation exposure. The purpose of this study was to evaluate the feasibility of 3D-US in daily target localization for APBR. Materials and methods: Forty-seven patients with stage I breast cancer who underwent breast conserving surgery were treated with a 2-week course of APBR. Patients with visible lumpectomy cavities on high quality 3D-US images were included in this analysis. Prior to each treatment, X-ray and 3D-US images were acquired and compared to images from simulation to confirm accurate position and determine shifts. Volume change of the lumpectomy cavity was determined daily with 3D-US. Results: A total of 118 images of each modality from 12 eligible patients were analyzed. The average change in cavity volume was 7.8% (range, -24.1% to 14.4%) on 3D-US from simulation to the end-of-treatment. Based on 3D-US, significantly larger shifts were necessary compared to portal films in all three dimensions: anterior/posterior (p = 7E-11), left/right (p = 0.002), and superior/inferior (p = 0.004). Conclusion: Given that the lumpectomy cavity is not directly visible via X-ray images, accurate positioning may not be fully achieved by X-ray images. Therefore, when the lumpectomy cavity is visible on US, 3D-US can be considered as an alternative to X-ray imaging during daily positioning for selected patients treated with APBR, thus avoiding additional exposure to ionizing radiation.

• 한국음향학회지
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• 제30권5호
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• pp.255-264
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• 2011

3차원 공간에서 음원으로부터 사람의 귀로 음향적인 전달 과정을 표현하는 머리전달함수는 사람이 음원의 위치를 판단할 수 있는 중요한 정보를 포함하고 있으며, 이를 이용하여 실질적으로는 존재하지 않는 음원을 근사적으로 생성할 수 있다. 그러나 각 청자에 특화되지 않는 머리전달함수를 사용함으로 인해 전후 방향이나 상하 방향의 혼동이 발생하게 되어 음상정위 성능이 저하된다. 이 논문에서는 머리전달함수를 통해 생성된 입체음향을 인간의 청각 특성을 사용하여 개선하는 알고리즘을 제안한다. 머리전달함수가 적용된 사운드 신호의 전역 마스킹 값을 계산한 후, 청자에게 크게 영향을 미치는 주파수 대역만을 추출하여 이를 강조함으로서 각 방향에 해당하는 인지 특성을 부각시키는 방법을 제안하였으며, 제안된 방법의 성능을 청감테스트를 통해 증명하였다.

• Radiation Oncology Journal
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• 제11권1호
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• pp.167-174
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• 1993

Recently, stereotactic radiosurgery plan is required with the information of 3-D image and dose distribution. A project has been doing if developing LINAC based stereotactic radiosurgery since April 1991. The purpose of this research is to develop 3-D radiosurgery planning system using personal computer. The procedure of this research is based on two steps. The first step is to develop 3-D localization system, which input the image information of the patient, coordinate transformation, the position and shape of target, and patient contour into computer system using CT image and stereotactic frame. The second step is to develop 3-D dose planning system, which compute dose distribution on image plane, display on high resolution monitor both isodose distribution and patient image simultaneously and develop menu-driven planning system. This prototype of radiosurgery planning system was applied recently for several clinical cases. It was shown that our planning system is fast, accurate and efficient while making it possible to handle various kinds of image modalities such as angiography, CT and MRI. It makes it possible to develop general 3-D planning system using beam's eye view or CT simulation in radiation therapy in future.