Research On The Visualization Of 3D Data Sets Based On Volume Rendering

Visualization in Scientific Computing (VISC) is a kind of newly developed subject in the 1980s. It is based on computer graphics and image manipulation technology, and the data generated in the procedure and the calculation results will be changed graphics or images, which are displayed on the screen for interactive processing. The core of visualization in scientific computing is visualization of three dimensional spatial data sets. There are several algorithms for visualization. The direct volume rendering is a rapidly developed visualization method of three dimensional data sets in recent years and is a hot research field, which has much research value and future application.In this thesis, several rendering methods of visualization of three dimensional data sets are discussed firstly, and their characters and differences are analyzed. Several typical and common algorithms of the volume rendering are described. The basic concepts and key technology of the volume rendering, including the optical modal, classification, designing of the transfer function, gradient estimating, space transformation, projection transformation and image composition are analyzed. Specially, different opacity transfer functions are designed for different volume data sets by analyzing the grey histograms.A method of the volume rendering based on the texture-mapping is studied and realized. The approach uses 2D or 3D textured data slices, and makes the 3D image using a blending operator. This approach described here is similar to ray casting. Unlike ray casting, in which each image pixel is built up ray by ray, this approach takes advantage of spatial coherence. The texture-mapping based approach processes all rays simultaneously, one 2D layer at a time. Since an entire 2D slice of the voxels are "cast" at one time, the algorithm is much more efficient than ray casting, and can be implemented on commodity PC. In this dissertation, the method is divided into two approaches, one using 2D textures, the other using a 3D texture. For the disadvantages of the method, some modification about 2D texture-mapping based volume rendering is presented, using different textures to avoid distortion when doing close-ups of the volume data. For volume rendering based on 3D texture-mapping, a method of calculating the vertices of the sliced polygon perpendicular to the line of sight is used and fine rendering effect is obtained.Finally, a primary visualization system is designed and developed, which is based on the texture-mapping volume rendering algorithms presented in this dissertation. The system can be migrated to different operating systems. Java 3D technology is used in the realization process. The experimental results used different data sets demonstrate the effectiveness of the proposed algorithms.