Study On Underwater Line Structured Light Measurement Technology Based On Monocular Vision

In order to achieve the underwater line structured-light measurement, combinedwith the image processing technique and line structured-light measurement technique,an underwater line structured-light measurement system based on the monocularvision is designed. After the model of system is established, it is calibrated byadopting the planar gridding target. Then the land line structured-light measurementmethod is introduced into the underwater measurement using the refractioncompensation algorithm. Finally, the feasibility of the underwater measurementsystem is verified by the experiments done in the water.The main contents of this paper are as follows:1. A simple and feasible calibration method of camera is presented. A planargridding target with known-distances between the lines is designed. Capturing thetarget images, the intersection points of the lines are extracted which are thecalibration points. And considering the influence of the distortion of lens, thesepoints are corrected by the compensation method. Then the accuracy of thecalibration is improved by adopting the radial alignment constraint calibrationmethod of two-steps.2. A method for calibrating the line structured-light system based on the planargridding target is proposed. Considering these calibration points extracted eachtime are collinear, the target is located at different positions for solving thisproblem. By freely moving the target, several images are captured, and moredifferent collinear calibration points are obtained which constitute thenon-collinear calibration points. According to the principle of cross ratioinvariance of the perspective projection, the relative position relationship of thelaser plane and the camera is calibrated.3. An underwater line structured-light measurement system based on the monocularvision is designed. This system is composed of control structure, waterproof case,a camera and a laser projector. Laser projector emits a laser plane which isprojected onto the measured object to form a laser stripe on the surface of theobject. According to the position and orientation of each point of the laser stripeon the image, the formula of light transmission is obtained through a series ofcalculation. Adopting the refraction principle, the data deviations caused by refraction of water surface are reduced by compensating algorithm. Finally, theunderwater line structured-light measurement based on the monocular camera isaccomplished by calculating the three-dimensional coordinates of all the pointsaccording to the system model considering the refraction.4. The control program of the underwater line structured-light measurement systembased on monocular camera is developed. This program contacts with thecorresponding hardware drive program and is written in Visual C++6.0softwaredevelopment environment. Through the accomplishment of the camera calibration,line structured-light system calibration, refraction compensation algorithm andunderwater line structured-light measurement and the real-time monitoring of themeasurement data, the calibration of intrinsic and extrinsic parameters andunderwater measurement are realized which provide the basis and convenience forthe subsequent scientific research.This paper establishes an underwater line structured-light measurement systemmodel based on the refraction compensation. A refraction compensation method isproposed for this model, and the underwater structured-light measurement methodbased on monocular vision is designed. The experiments verify the accuracy andreliability of the method.