# Research on a Measurement Method for the Ocean Wave Field Based on Stereo Vision
###### Abstract
First, the Moravec corner points were extracted from the top layer of a pyramidal image. Then, the left and right images were extracted. Next, the corner points that were extracted from the top-level image of the pyramid were matched based on the principle of a maximum cross-correlation measure, thus obtaining the top-level matching pair set. In the matching pair sets, each matching pair was in the corresponding lower-level area of the pyramid and then matching that was based on a maximum cross-correlation measure was performed. After that, the matching sets of the left and right images were obtained. This feature matching method provides matching pairs as coordinates for the three-dimensional reconstruction of waves and, in this way, realizes sea surface wave measurement. However, the matched results that are obtained via this method have many mismatches. Accordingly, in the future, complex algorithms need to be introduced in order to eliminate the mismatches, alternatively algorithmically accurate wave heights can be introduced in the three-dimensional reconstruction [20]. In 2014, [PERSON] et al. achieved the acquisition of wave crest coordinates based on contour extraction technology, which reduced the influence of the acquisition accuracy on the two-dimensional coordinates of the wave crest in non-contact wave photogrammetry technology, but only the wave's crest was studied [21]. This paper presents a comprehensive process algorithm of wave measurement that is based on stereo vision. 1. The matching part utilizes the gridding siftGPU method, wherein first the common area of the left and right cameras is determined and, then, grid zoning for the common area is carried out. The grid coordinates of the left camera are used to preliminarily locate the corresponding grid coordinates of the right camera and GPU multithreading processingis used in order to realize multi feature points and fast matching. Compared with the conventional siftGPU, the matching time with the proposed approach can be controlled below 6 s while the number of matching points can be maintained above 20,000, an outcome that is evidently much better than that of the traditional siftGPU algorithm. 2. In this paper, the least squares method and wave theory are used to normalize the sea surface-based plane calibration, plane error point fitting, and wave parameter inversion. The design's method is simple and feasible. Compared with the traditional wave height meter, the wave height range is 0.2 m-1 m, the measurement error is less than 10%, and the periodic measurement error is less than 0.5 s.
3. The Hough transform and least squares method have been used herein to calculate the wave's direction value. It was observed that, for a given wave image, the detection results and the original direction are basically the same. The rest of this paper is organized as follows. Section 2 introduces the whole process of utilizing the algorithm of wave measurement that is based on stereo vision. Section 3 presents the experimental tests and results. Finally, the conclusions and directions for future work are given in Sections 4 and 5.