Three-dimensional Data Field Volume Rendering And Achieve

3D data fields are a hot research area in scientific visualization, which are also met generally in practical applications. Among all the visualization methods, direct rendering of 3D data fields is a very important approach. Compared with the isosurface extraction approach, direct volume rendering processes all samples to make images without producing the intermediate geometric elements. Therefore, many contents can be displayed together in a single image, which benefits scientists to comprehend data.Although the direct volume rendering approach has many advantages, they cannot render data very quickly and their rendered images are in general blur, which hinders scientists from understanding data in high efficiency. As for this, the author has done much work as follows.1) By finding a transparent degree unit to unify different transparent values of samples, a transparent degree ruler is built to describe the transparency accumulation. Based on such a ruler, the fundamental operation of the volume rendering methods, color composition, can be transferred to execute along the ruler, which may save a lot of time as only add operations are in demand.2) According to the color composition method by distributing colors over a 2D virtual plane, much 3D information of volumes and some intermediate rendered images can remain on the virtual plane. Therefore, a new interactive visualization method is put forward by deriving three interactive tools operating on the virtual plane. With this fast interactive method, scientists can study the interesting parts conveniently.3) Splatting is a very famous projection method in volume rendering. However, it is utilized in an approximative way when irregular volumes are rendered, which certainly injures the image quality. By using the sine function to uniformly scale samples in different sizes, a variable splatting algorithm is proposed to have different samples accumulate colors in high precision, which may greatly improve the image quality.4) Shading is an important tool in visualization. But it cannot be efficiently employed in the projection approach which has the fame to render volumes fast. In this thesis, we present a method by using sphere and ellipsoid surfaces to approximate the material interfaces in volumes. Therefore, the material interfaces can be easily shaded and integrated efficiently in the projection approach.5) In irregular volumes, as the shape and size of samples are not constant, the rendering speed and the image quality are far from satisfaction. As for this, we put forward a method to solve the problem of cell queue up based on setting up linking nodes, and then combine the raycasting approach and the projection approach to render irregular volumes fast with images in high quality.6) Rendering geometric objects and volumes together is always an important area in scientific visualization. Although many methods have been proposed, they have not completely solved the problem of intersection between geometric objects and volume samples, and have not employed the projection approach in the rendering process, which is in general faster than the raycasting approach. After investigating the intersection situation, we present a method by taking linking nodes to integrate the projection approach which not only completely solve the intersection problem, but also render the geometric objects and volumes together in high efficiency.