Study On Underwater Positioning System Based On Binocular Stereo Vision

Ocean has abundant resources and vast space, it is conductive for humans to keep asustainable development for a long time that developing the marine science and utilizingthe marine resources reasonably. Vision technology, an important underwater detectionmeans, is usually equipped with underwater robots. For underwater detection in a smalldistance, vision technology has lots of advantages, such as non-contact, high precision andlarge amount of information. This paper conducts systematic researches on underwaterbinocular stereo vision from three aspects, namely camera imaging model underwater,calibration and positioning, which has a certain guiding significance for the application ofunderwater binocular stereo vision. The specific tasks as follows:Firstly, camera has to be equipped with waterproof when working underwater, whichleads the imaging light refracted through the different medium, such as water, waterproofand air, so the imaging model will be changed. This paper builds the ideal underwatermodel with parallel optical axis and the general underwater model with freedom opticalaxis on the basis of camera imaging model.Secondly, because of the changes on imaging model when working underwater,traditional calibration means can not calibrate the parameters correctly, so a two-stepcalibration means for underwater camera is proposed. First of all, camera basic parametersis calibrated by Zhang’s means in the air, and then by building the evaluation function tocalibrate the systematic parameters, which is composed by the actual image pointcoordinates minus the coordinates calculated by the model.Thirdly, underwater positioning algorithm is studied with two models. In the idealmodel, the formula of image point and space point is proposed by triangular geometry. Inthe general model, the space point coodinate can be calculated by vector geometry andquaternions. At last, error analysis of positioning model is studied, which is useful tooptimize structure design and improve the accuracy of system.