• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2013.05a
• /
• pp.311-314
• /
• 2013

방사왜곡, 접선왜곡으로 인해 영상의 왜곡이 발생한다. 왜곡 영상은 시각적인 문제 외에도 영상분석을 통해 정확한 수치 계산을 통해 영상을 처리할 때, 문제가 되기 때문에 영상을 보정해 주어야한다. 감시 시스템, 로봇의 시각 역할 등 다양한 비전 시스템에서 카메라가 장착되어 왜곡보정에 대한 사용도가 증가 하고 있다. 그리고 한 광각 카메라에서 획득한 영상은 비선형적인 방사 왜곡을 가지고 있기 때문에 정확한 영상을 획득하기 위해서는 왜곡 보정 작업을 수행하여야 한다. 왜곡된 영상을 올바르게 보정 해줄 캘리브레이션(Calibration)은 영상 좌표계의 한 점이 실세계 좌표계의 어느 위치에 대응하는지를 결정하기 위해 보정 변수들을 결정하는 과정이다. 본 논문에서는 캘리브레이션(Calibration)을 수행할 때 패턴 개수, 이미지 파일 크기, 이미지 파일 개수가 영상 왜곡 보정에 어떤 영향을 미치는지 분석해 보았을 때 다른 어떤 경우보다 패턴 개수를 비교적 작게 했을 때의 경우가 뚜렷한 차이를 보여주었다.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
• /
• v.7 no.2
• /
• pp.45-51
• /
• 1989

Lens distortion would produce image displacement, therefore correction of lens distortion is required urgently to improve accuracy of results in photogrammetry. The objective of this study is to find out lens distortion coefficients versus focussing distance on non-metric and metric camera and to investigate propriety of application of lens distortion coefficients to three dimensional analysis. Analytical plumb line method which needs not perform control survey and space resection and requires only one photograph was used in order to get lens distortion coefficients. As the result of this study, the coefficients of radial and tangential distortion change as focussing distance changes, and consequently it is reasonable to apply the eigenvalues of lens distortion coefficients according to focussing distance. When these coefficients were applied to actual measurement, standard errors decreased about 30% or 76% remarkably.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.12 no.2
• /
• pp.151-159
• /
• 1992

In close-range photogrammetry, to employ non-metric camera especially for the purpose of precise measurement, systematic errors must, first of all, be corrected as they have a great influence on accuracies of results. For it, fiducial marks was built in non-metric camera and the factors such as PPS, PPA, EFL, CFL, and radial lens distortion coefficients for each quadrant were calibrated through collimator test. Also, the coefficients of both radial and tangential lens distortion were calibrated from analytical plumb line method and therefore main systematic errors could be effectively corrected. Using the calibrated non-metric camera, close-range photogrammetry could be successfully accomplished and accuracies could be improved sharply.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.40 no.7
• /
• pp.417-427
• /
• 2016

This paper is the first investigation of the steady flow characteristics of an SI engine with a semi-wedge combustion chamber as a function of the port shape. For this purpose, the planar velocity profiles were measured at the 1.75B position by particle image velocimetry. The flow patterns were examined with both a straight and a helical port. Two swirls were observed up to 4 mm valve lift with the straight port and up to 2 mm with the helical one; however, only one swirl was present after these lifts. The flow characteristics changed suddenly between 4 and 5 mm lift in the straight port; on the other hand, the change with lift was gradual with the helical port - the transition points between flow regimes were different with the port shapes. In addition, the centers of the swirls were relatively far from the cylinder center so that the effect of eccentricity may not be negligible at 1.75B, regardless the shape. The eccentricity values with the straight port were especially high - over 0.5 for all lifts. Finally, real velocities were found to be much lower than those predicted by the assumption of ISM evaluation, with the profiles differing qualitatively as well.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.41 no.2
• /
• pp.97-107
• /
• 2017

This study is the second investigation on the steady flow characteristics of an SI engine with a semi-edge combustion chamber as a function of the port shape with varying evaluation positions. For this purpose, the planar velocity profiles were measured from 1.75B, 1.75 times of bore position apart from the bottom of head, to 6.00B positions using particle - image velocimetry. The flow patterns were examined with both a straight and a helical port. The velocity profiles, streamlines, and centers of swirl were almost the same at the same valve lift regardless of the measuring position, which is quite different from the case of the pent-roof combustion chamber. All the eccentricity values of the straight port were out of distortion criterion 0.15 through the lifts and the position. However, the values of the helical port exceeded the distortion criterion by up to 4 mm lift, but decreased rapidly above the 3.00B position and the 5 mm lift. There always existed a relative offset effect in the evaluation of the swirl coefficient using the PIV method due to the difference of the ideal impulse swirl meter velocity profile assumption, except for the cylinder-center-base estimation that was below 4 mm of the straight port. Finally, it was concluded that taking the center as an evaluation basis and the assumption about the axial velocity profile did not have any qualitative effect on swirl evaluation, but affected the value owing to the detailed profile.