Analysis of Effect on Camera Distortion for Measuring Velocity Using Surface Image Velocimeter

Jun Hyeong Lee; Byung Man Yoon; Seo Jun Kim

doi:10.17820/eri.2021.8.1.001

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2021 Vol.8, Issue 1 Next Page

Original Article

Analysis of Effect on Camera Distortion for Measuring Velocity Using Surface Image Velocimeter 표면영상유속측정법을 이용한 유속 측정 시 카메라 왜곡 영향 분석

31 March 2021. pp. 1-8

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Abstract

A surface image velocimeter (SIV) measures the velocity of a particle group by calculating the intensity distribution of the particle group in two consecutive images of the water surface using a cross-correlation method. Therefore, to increase the accuracy of the flow velocity calculated by a SIV, it is important to accurately calculate the displacement of the particle group in the images. In other words, the change in the physical distance of the particle group in the two images to be analyzed must be accurately calculated. In the image of an actual river taken using a camera, camera lens distortion inevitably occurs, which affects the displacement calculation in the image. In this study, we analyzed the effect of camera lens distortion on the displacement calculation using a dense and uniformly spaced grid board. The results showed that the camera lens distortion gradually increased in the radial direction from the center of the image. The displacement calculation error reached 8.10% at the outer edge of the image and was within 5% at the center of the image. In the future, camera lens distortion correction can be applied to improve the accuracy of river surface flow rate measurements.

Keywords

Camera lens distortion

Distortion correction

Surface Image Velocimeter

표면영상유속측정법은 일반적으로 상호상관법을 이용하여 수표면을 촬영한 연속된 두 영상에서 입자군의 명암값 분포를 계산하여 입자군의 변위를 계산하고 이를 두 영상 사이의 시간 간격으로 나누어 입자군의 이동 속도를 산정하는 방법이다. 따라서 표면영상유속측정법으로 산정한 유속의 정확도를 높이기 위해서는 영상 내 두 입자군의 변위를 정확하게 계산하는 것이 무엇보다 중요하다. 즉, 분석하고자 하는 영상에서 입자군이 이동한 물리거리를 정확하게 계산할 수 있어야 한다. 하지만 카메라를 이용하여 실제 하천을 촬영한 영상은 카메라 렌즈에 의한 왜곡이 필연적으로 발생하게 되고 이는 영상 내의 변위 산정 시에도 영향을 미친다. 이에 본 연구에서는 간격이 일정한 격자보드를 이용해, 카메라 렌즈 왜곡이 변위 산정 결과에 미치는 영향을 분석하였다. 연구 결과 카메라 렌즈 왜곡은 영상 중심에서 방사방향으로 점점 크게 나타났으며 변위 산정 오차는 영상 외곽에서 최대 8.10%, 영상 중심 부근에서 5% 이내로 나타났다. 따라서 표면영상유속측정법을 이용하여 하천의 유속 측정 시 카메라 렌즈 왜곡 보정을 실시하여 표면유속 측정 결과의 정확도를 개선하면 하천의 표면유속을 보다 정확하게 측정할 수 있을 것으로 기대된다.

키워드

카메라 렌즈 왜곡

영상 왜곡 보정

표면영상유속측정법

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Information

Publisher :Korean Society of Ecology and Infrastructure Engineering
Publisher(Ko) :응용생태공학회
Journal Title :Ecology and Resilient Infrastructure
Journal Title(Ko) :응용생태공학회 논문집
Volume : 8
No :1
Pages :1-8
Received Date : 2020-12-17
Revised Date : 2020-12-22
Accepted Date : 2020-12-22
DOI :https://doi.org/10.17820/eri.2021.8.1.001

Ecology and Resilient Infrastructure ISSN:2288-8527(Online) 응용생태공학회 논문집

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