• Title/Summary/Keyword: Relative distance

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Mono-Vision Based Satellite Relative Navigation Using Active Contour Method (능동 윤곽 기법을 적용한 단일 영상 기반 인공위성 상대항법)

  • Kim, Sang-Hyeon;Choi, Han-Lim;Shim, Hyunchul
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.43 no.10
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    • pp.902-909
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    • 2015
  • In this paper, monovision based relative navigation for a satellite proximity operation is studied. The chaser satellite only uses one camera sensor to observe the target satellite and conducts image tracking to obtain the target pose information. However, by using only mono-vision, it is hard to get the depth information which is related to the relative distance to the target. In order to resolve the well-known difficulty in computing the depth information with the use of a single camera, the active contour method is adopted for the image tracking process. The active contour method provides the size of target image, which can be utilized to indirectly calculate the relative distance between the chaser and the target. 3D virtual reality is used in order to model the space environment where two satellites make relative motion and produce the virtual camera images. The unscented Kalman filter is used for the chaser satellite to estimate the relative position of the target in the process of glideslope approaching. Closed-loop simulations are conducted to analyze the performance of the relative navigation with the active contour method.

Penalizing the Negative Exponential Disparity in Discrete Models

  • Sahadeb Sarkar;Song, Kijoung-Song;Jeong, Dong-Bin
    • Communications for Statistical Applications and Methods
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    • v.5 no.2
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    • pp.517-529
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    • 1998
  • When the sample size is small the robust minimum Hellinger distance (HD) estimator can have substantially poor relative efficiency at the true model. Similarly, approximating the exact null distributions of the ordinary Hellinger distance tests with the limiting chi-square distributions can be quite inappropriate in small samples. To overcome these problems Harris and Basu (1994) and Basu et at. (1996) recommended using a modified HD called penalized Hellinger distance (PHD). Lindsay (1994) and Basu et al. (1997) showed that another density based distance, namely the negative exponential disparity (NED), is a major competitor to the Hellinger distance in producing an asymptotically fully efficient and robust estimator. In this paper we investigate the small sample performance of the estimates and tests based on the NED and penalized NED (PNED). Our results indicate that, in the settings considered here, the NED, unlike the HD, produces estimators that perform very well in small samples and penalizing the NED does not help. However, in testing of hypotheses, the deviance test based on a PNED appears to achieve the best small-sample level compared to tests based on the NED, HD and PHD.

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Real-time Location Tracking System Using Ultrasonic Wireless Sensor Nodes (초음파 무선 센서노드를 이용한 실시간 위치 추적 시스템)

  • Park, Jong-Hyun;Choo, Young-Yeol
    • Journal of Institute of Control, Robotics and Systems
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    • v.13 no.7
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    • pp.711-717
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    • 2007
  • Location information will become increasingly important for future Pervasive Computing applications. Location tracking system of a moving device can be classified into two types of architectures: an active mobile architecture and a passive mobile architecture. In the former, a mobile device actively transmits signals for estimating distances to listeners. In the latter, a mobile device listens signals from beacons passively. Although the passive architecture such as Cricket location system is inexpensive, easy to set up, and safe, it is less precise than the active one. In this paper, we present a passive location system using Cricket Mote sensors which use RF and ultrasonic signals to estimate distances. In order to improve accuracy of the passive system, the transmission speed of ultrasound was compensated according to air temperature at the moment. Upper and lower bounds of a distance estimation were set up through measuring minimum and maximum distances that ultrasonic signal can reach to. Distance estimations beyond the upper and the lower bounds were filtered off as errors in our scheme. With collecting distance estimation data at various locations and comparing each distance estimation with real distance respectively, we proposed an equation to compensate the deviation at each point. Equations for proposed algorithm were derived to calculate relative coordinates of a moving device. At indoor and outdoor tests, average location error and average location tracking period were 3.5 cm and 0.5 second, respectively, which outperformed Cricket location system of MIT.

Evaluation on the Relationship between Mask Imaging Performance and Standoff Distance of EUV Pellicle (EUV pellicle의 standoff 거리에 따른 이미지 전사 특성 평가)

  • Woo, Dong Gon;Hong, Seongchul;Kim, Jung Sik;Cho, Hanku;Ahn, Jinho
    • Journal of the Semiconductor & Display Technology
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    • v.15 no.1
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    • pp.22-26
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    • 2016
  • Extreme ultraviolet (EUV) pellicle is one of the most concerned research in the field of EUV lithography (EUVL). Imaging performance of EUV mask with pellicle should be investigated prior to high volume manufacturing (HVM) of EUVL. In this paper, we analyzed the relationship between standoff distance and imaging performance of EUV mask to verify the influences of relative standoff distance on imaging performance. As a result, standoff distance of EUV pellicle has no effect on imaging performance of EUV mask such as critical dimension (CD), normalized image log slope (NILS) and image contrast. Therefore, pellicle support structure can be flexibly designed and modified in diverse ways to complement the thermal limitation of EUV pellicle membrane.

Removal Method of Signal Interference between Ultrasound Sensors (초음파 센서 간 신호 간섭 제거 방법)

  • Im, Hyungchul;Lee, Seongsoo
    • Journal of IKEEE
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    • v.25 no.4
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    • pp.584-590
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    • 2021
  • This paper proposes a removal method of signal interference between ultrasound sensors where ghost signals due to interference are excluded and correct signal is recognized in distance mensurement using ultrasound sensors. The proposed method detects and excludes ghost signals when previous measured distance is compared to current measured distance and the distance difference exceeds a threshold. The threshold is fixed in conventional methods, so ghost signals cannot be correctly excluded when ultrasound sensor or target object move rapidly. On the contrary, to improve accuracy, the threshold is not fixed in the proposed method, and the threshold is adpatively determined based on the relative velocity when ultrasound sensor or target object move. Experiments of distance measurement with ultrasound signal interference are carried out where multiple ultrasound sensors of same type are exploited with maximum interference, and the results show that the proposed method efficiently exclude ghost signals.

Relative localization errors: The effect of reference location on the errors (상대적인 위치지각의 왜곡: 참조자극의 위치가 왜곡에 미치는 영향)

  • Li, Hyung-Chul
    • Korean Journal of Cognitive Science
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    • v.15 no.3
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    • pp.15-24
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    • 2004
  • The perceived position of a flashing target object is generally biased towards the direction of eye movement when there is no reference around the target. Current research examined the localization accuracy of a flashing target relative to a static reference. The perceived location of the target relative to the reference was distorted and the pattern of perceptual distortion systematically depended on the position of the reference relative to the target. This kind of result was consistently observed regardless of the distance between the reference and the target and direction of pursuit eye movement. We have discussed how these results could he explained by the theories previously suggested to explain the localization of objects.

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A study on the effect of changes in the level of environmental regulation of the importing country on export performance (수입국 환경제도수준 변화가 수출에 미치는 영향 연구)

  • Yun-Seop Hwang;Cheon Yu
    • Korea Trade Review
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    • v.45 no.4
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    • pp.65-81
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    • 2020
  • Under New Climate Regime, countries are trying to enhance environmental regulations to meet international standards. This study is designed to examine the relationship between the relative level of environmental regulation of the importing countries and the export performance at the industrial level. Panel data from 2009 to 2018 was established for 12 top export industries and empirical analysis was conducted. For the analysis method, panel OLS, Hausman-Taylor, and panel GLS were used based on the results of the Hausman verification. The dependent variable is the export performance of each industry. As the independent variables, the relative level of environmental regulation, GDP per capita of the importing country, exchange rate, FTA agreement, and physical distance from the importing country were used. Results show that the relative level of environmental regulation has a negative effect on export performance of semiconductors, displays, special machines, general machines, electric appliances, and home appliances. On the other hand, there are no relationship between the relative level of environmental regulation of the importing country and export performance of automobile, petroleum refining, petrochemical, shipbuilding, and communication equipment industries.

A Camera Pose Estimation Method for Rectangle Feature based Visual SLAM (사각형 특징 기반 Visual SLAM을 위한 자세 추정 방법)

  • Lee, Jae-Min;Kim, Gon-Woo
    • The Journal of Korea Robotics Society
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    • v.11 no.1
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    • pp.33-40
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    • 2016
  • In this paper, we propose a method for estimating the pose of the camera using a rectangle feature utilized for the visual SLAM. A warped rectangle feature as a quadrilateral in the image by the perspective transformation is reconstructed by the Coupled Line Camera algorithm. In order to fully reconstruct a rectangle in the real world coordinate, the distance between the features and the camera is needed. The distance in the real world coordinate can be measured by using a stereo camera. Using properties of the line camera, the physical size of the rectangle feature can be induced from the distance. The correspondence between the quadrilateral in the image and the rectangle in the real world coordinate can restore the relative pose between the camera and the feature through obtaining the homography. In order to evaluate the performance, we analyzed the result of proposed method with its reference pose in Gazebo robot simulator.

Hydrodynamic interaction between two cylinders in planar shear flow of viscoelastic fluid

  • Jung, Hyun-Wook;Daejin Won;Kim, Chongyoup
    • Korea-Australia Rheology Journal
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    • v.14 no.4
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    • pp.203-207
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    • 2002
  • Particle-particle interaction is of great importance in the study of suspension rheology. In this research we have investigated the hydrodynamic interaction between two identical cylinders in viscoelastic fluids numerically as a model problem for the study of viscoelastic suspension. We confine two neutrally buoyant cylinders between two parallel plates and impose a shear flow. We determine the migration velocity of two cylinders. The result shows that cylinders move toward or away from each other depending upon the initial distance between them and that there is an equilibrium distance between two cylinders in viscoelastic fluids regardless of the initial distance. In the case of Newtonian fluid, there is no relative movement as expected. The results partly explain the chaining phenomena of spherical particles in shear flows of viscoelastic fluids.

Negative Exponential Disparity Based Robust Estimates of Ordered Means in Normal Models

  • Bhattacharya, Bhaskar;Sarkar, Sahadeb;Jeong, Dong-Bin
    • Communications for Statistical Applications and Methods
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    • v.7 no.2
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    • pp.371-383
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    • 2000
  • Lindsay (1994) and Basu et al (1997) show that another density-based distance called the negative exponential disparity (NED) is an excellent competitor to the Hellinger distance (HD) in generating an asymptotically fully efficient and robust estimator. Bhattacharya and Basu (1996) consider estimation of the locations of several normal populations when an order relation between them is known to be true. They empirically show that the robust HD based weighted likelihood estimators compare favorably with the M-estimators based on Huber's $\psi$ function, the Gastworth estimator, and the trimmed mean estimator. In this paper we investigate the performance of the weighted likelihood estimator based on the NED as a robust alternative relative to that based on the HD. The NED based estimator is found to be quite competitive in the settings considered by Bhattacharya and Basu.

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