Research On 3-D Visualization Technology For Ocean Scalar Field

With the continuous development of marine science and the improvement of the marine exploration technology, vast amounts of oceanographic data are obtained by using various technical methods, such as ocean satellite remote sensing technology, buoy-detection technology and marine research ship surveying. Marine data is a reflection of the ocean phenomena. Using digital means to process and represent marine data so that more useful information hidden in the data can be expressed adequately is an important area of research in the field of marine science, and it is an effective way to better understand marine phenomena and do further oceanographic research. Information visualization technology applied in the field of ocean science is an effective mean for the digital expression of marine data and marine phenomena.In this paper, the research is based on the information visualization technology. According to the characteristics of the marine scalar data, this paper focuses on studying the three-dimensional visualization algorithm of marine scalar field to make the characteristics of the ocean can be effectively expressed. It Designs and implements a visualization system of marine scalar field is Designed and implemented. Based on GPU acceleration algorithm, the system realizes real-time rendering of ocean data and supports all kinds of interactive operation such as sections selection, custom color scheme setting, and so on. The main work of the paper and research results obtained of the paper are as follows:(1)Analysis of marine data types and the corresponding visualization methodsThe characteristics of marine data are analyzed and researched, and based on the characteristics, marine data is classified into different types. According to of the characteristics, the physical property characteristics of the data, the visual marine data is divided into two types:scalar field data and vector field data, and the general visualization methods of the two types are explored respectively. Research focuses on analyzing the three-dimensional visualization methods of marine scalar field data and presents an implementation of three-dimensional visualization for satellite cloud images. Meanwhile the principle of volume rendering visualization is analyzed, laying the foundation for improving the volume rendering visualization algorithm for scalar field characteristics.(2)Improvement of volume rendering visualization algorithm for ocean scalar field characteristicsThe characteristics of the ocean scalar data are analyzed and studied, and the ray-casting algorithm for volume rendering is improved based on the features. Generally, the present three-dimensional marine data are composed of multi-section data which is uneven along the z-axis(depth). There is a problem for the uneven multi-section oceanic volume data that how to be organized to guarantee the data matches its actual geographic depth when rendering. When using the ray-casting algorithm, because the section intervals of the data are non-uniform, adopting fixed step when sampling will lead to some negative outcomes, one is that the high resolution data can’t be sampled adequately, and another is that invalid sampling is executed repeatedly in the lower resolution data region. So an improvement of the ray-casting algorithm for the multi-section oceanic scalar field volume data is put forward. Organize the volume data into 3-D texture, and based on the ray-casting algorithm on GPU, back calculate the volume texture coordinate of the sampling point use its texture coordinate in the bounding-box, then sample the volume data with the texture coordinate, so that the correspondence between the data and its geographical spatial relations is achieved. Meanwhile, calculate the sampling step according to the section interval of the data region where the sampling point is, in this way the data is sampled by adaptive-step and the amount of computation will be reduced when rendering.(3) Designing transfer functions for the features of the ocean scalar fieldDue to the different characteristics with different data, different transfer functions should be designed based on different ocean features, so that volume rendering technology will real work in the expression of the ocean features. Based on the system function of interactive setting parameters for visualization, reasonable transfer functions can be setting to control the color parameters of different data values to express the scalar field characteristics.(4) Designing and implementing a three-dimensional visualization system for marine scalar fieldBased on the framework of i4Ocean, the existing oceanographic visualization system, a three-dimensional visualization system for marine scalar field is designed and implemented. The improved volume rendering algorithm for the marine scalar data is applied in the system. In order to express the ocean phenomena more intuitively and efficiently, the ocean elements and distribution features are visualized in the three-dimensional space. In the meantime, various system functions are achieved, such as real-time rendering for the three-dimensional marine scalar field data, setting parameters for visualization interactively, selecting and rendering sections of the data interactively, fusion display between terrain data and ocean scalar field data.