Research On The Volume Rendering Of Global Scalar Data Basing On Hexagonal Mesh

Volume rendering has been widely used in the visualization of the global data, such as meteorology, ocean, geology and so on, because of its advantage of observing the whole and complete picture of the 3D data field. To get a more precise volume rendering, a high precision volume data is essential. Due to the "pole problem" of latitude and longitude grid which is widely used by traditional volume rendering method, a lot of unnecessary data will be generated when constructing volume data in the high latitude area. It not only increases the quantity of data, but also decreases the accurancy of volume rendering. In recent years, the spherical discrete grid system with triangle, diamond and hexagon as the basic unit has made great progress, which overcomes the pole problem radically. In view of the present situation, this paper proposes the application of hexagonal grid in volume rendering, which can effectively reduce the quantity of data and improve the rendering efficiency.Firstly, after analyzing the spherical discrete grid of different split cell, the spherical hexagon grid is chosen as the grid system and the topology structure is saved. According to the original data, the scalar value of each hexagonal cell is calculated by interpolating the original data, and finally the volume data based on hexagonal grid is formed.Secondly, a triangle can be formed by the center of 3 adjacent hexagonal elements, so a series of triangular elements are obtained from the topological structure of the hexagonal grid. And the code of triangular elements is actually the code of hexagonal vertices. To accelerate the conversion of latitude and longitude to the triangular element, a look-up table is generated to reduce the time cost of the ray casting phase in the preprocessing stage. In addition, all the possible situations of the conversion are analyzed, and the corresponding conversion methods are designed for different situations.Thirdly, the core part of the volume rendering- ray casting operation is parallelly processed on CUDA platform, and the other process is on the CPU. Basing on this architecture, a volume rendering method based on CUDA and hexagonal grid is designed. We can quickly obtain the intersection point of light and volume data by using the "render to texture" technology. And the center of gravity interpolation method is applied in the process of interpolation.Finally, the prototype system is designed and implemented according to the method of this paper. On the basis of verifying the feasibility, we compared it with the traditional methods and the existing methods, the effectiveness of the method is proved. And also, the interaction process is optimized, which makes the interaction in the volume rendering scene more smoothly.