Skeleton Enhanced Line Drawing Researches On Three-dimensional Grid Model

Non-photorealistic rending technology, as the branch of computer graphics corresponding with realistic graphics, began to be the focus of computer graphics since1990s. Now the research achievements of non-photorealistic have been widely used in computer animation industry, computer art, and scientific data visualization et al.Line drawing is a classic non-photorealistic rending method which expresses the shape of object’s characteristics through concise lines as an art form for hundreds of years. Line drawing is also widely used in actual life in many fields. For example, many products instruction use line drawings to illustrate function unit, and line drawing also appears in the patent as well as textbooks and illustrations. We can also see that the architects often use line drawing to express the prototype design.The traditional line drawing technology is mainly based on local point’s information of the model instead of model’s whole pattern information. We introduce linear skeleton information into line drawing to express3D model’s overall information. On the basis of extracting contours and geometric region feature line, we append the skeleton guide feature line on the non-geometric region to rich the model details. Details are as follows:(1) We make the comprehensive analysis of the research status about the three-dimensional model linear skeleton extraction and line drawing techniques, and point out the important meanings and broad application prospects.(2) We use a linear skeleton interactive extraction method based on the convex hull and oriented bounding box to extract the skeleton. Through the improved segmentation algorithm based on the regional growth characteristics we cut the model into several parts, we make the real-time computing when we cut the model every time to be an preprocessing by simplifying the isophotic distance, and by this means we can reduce the running time; then we use convex hull OBB to extract the linear skeleton.(3) We introduce the linear skeleton information of3D models into line drawings to achieve better rendering results. First, we draw the model’s silhouette to depict the model’s boundary information; then we define the geometric characteristic weight value based on information such as vertices’differential curvature and torsion, then extract the geometric feature lines in geometric area by introducing the view-dependent torsion and divide the model into the geometric area and non-geometric region based on the above weight value. On that basis we extract the skeleton guided feature lines in non-geometric region, and then generate the final line drawing effect by adding the perception information into our method.(4) We use C++, OpenGL and CGAL to realize our algorithm and describe the main steps of our algorithm.At last, we make the summarizations of our work and give the further research directions.