| With the rapid development of computer graphics, the graphics with the goal of non-photorealistic rendering is coming to attach more and more importance. Non-photorealistic rendering (NPR) technique is a brand new and an animate branch of computer graphics. The images generated by NPR often resemble those that, for example, architects, industrial artists, or scientific illustrators produce to communicate more or specific information, often accompanied by text.Silhouette plays an important role in our visual interpretation of 3D shape, and they are necessary for both perception and taste, which represents the contour and basic shape of the model. Artists and designers therefore often emphasize silhouettes, either by drawing them explicitly or by contrast enhancement across silhouette boundaries. In cartoon, silhouettes are used for shape expressing, and broad brushes for main characters, and this method also frequently applies in the technical drawing. Silhouette detecting algorithms can be divided into two aspects, image space algorithm and object space algorithm.We can get the points directly from 3D scanners and the points can express the real geometry properties of the surface of objects. Furthermore, regarding some concrete applications, in consideration actual effect and in space and time price measuring, also often can choose with this kind simple, also the storage space very small fundamental element substitutes for the triangle. For instance, when the three-dimensional model is far away from us, or certain in ours gaze, we is not unnecessary partially, also does not need to go to construct the grid. In such situation, selects the points expression is one kind of good choice.In this paper, we draw silhouette from line drawing .Our research is mainly on how to draw silhouette fast, and draw the silhouette correctly on NPR. The main contributions of this paper are:1. We proposed a quad tree structure based on the norm vector sphere. The construction of three-dimensional model is most take the grid data as the foundation to the spatial region division. We need to establish the index structure of quad tree directly based on the cloud data .In this paper, unorganized point is as the input. First we take the vector of the point on the points cloud to the sphere ,... |
