To Draw The Silhouettes Based On 3D Points Cloud Model

Silhouette plays an important role in the research of Computer Graphics, Computer Vision and Pattern Recognition. It is an important factor to depict the shape of object. It is not only related to the result of the final rendering, but also the key to speed up the rendering process in the graphics application. There are so many kinds of lines to express the object shapes, such as silhouettes, contours, creases etc, and silhouette is the most important and effective in expressing the object shape. For painters, they can use silhouettes to express artistic effect. Thus the extraction of silhouettes of objects is a spot topic in such research fields as Computer Graphics and Computer Vision etc.With the development of 3D scanners technology, one can get the points directly from 3D surfaces and the points can express the real geometry properties of the surfaces of objects. Due to the advantage of not storing and maintaining the connectivity of the sampling points, the point cloud model has much more flexibilities on representing and processing the complicate or dynamic shapes compared with the mesh model. Therefore, the point cloud model becomes more popular in the related research areas as well as the industry.In this paper, we focus on how to extract silhouettes from points cloud model as quickly as possible. The main contributions of the work are:1,We proposed a method to extract silhouette points from points cloud model by using Gaussian sphere. Due to the point cloud model having no connectivity information, it is difficult to detect silhouette points quickly. We proposed a concept of hierarchical Gaussian Sphere. Based on the hierarchical structure, we detect the silhouette points in the point cloud models which are under perspective as well as parallel projection.2,We proposed an algorithm for connecting the silhouette points to be the silhouette lines in the model. Using the original positions of the silhouette points, we construct a crude silhouette line represented by a graph structure. Then, by the minimum spanning tree, tree pruning, and tree smoothing, we have the 3D refined silhouette lines.The silhouette lines provide a solid foundation for renderings of line drawings, as well as pattern recognitions in research as well as inindustry.