Research On Technology And Algorithm Of Geometry-based 3D Model

Digital watermarking is a useful technique for protecting the copyright of digital products. In recent years, more and more scholars are interested in this technique and do the related research in this field. With the application of Geometry-based 3D models in Manufacturing Network, cooperated design, digital museum and so on, the problem of the copyright protection is being one of the research interest in the field of watermarking research.This dissertation first introduces the related technique backgrounds, the frame work and the application field of information hiding and watermarking. And then the existing algorithms of the watermarking of Geometry-based 3D models are studied. The advantages and the shortcomings of the algorithms are analyzed. Two new watermarking algorithms are proposed in this dissertation.A new watermarking algorithm based on wavelet transform is proposed to deal with NURBS models. Firstly, three virtual images are gotten based on the control points of the NURBS representation of the original 3D model. Each pixel value of the virtual images is corresponding to the coordinate value which is corresponding to the control points of the original 3D model in the coordinate axes. Subsequently, these virtual images are decomposed by third-layer wavelet decomposition and the watermarking information is embedded in the low frequency coefficients. Finally, the marked virtual images are gotten with inverse wavelet transform and a new group of control points is obtained based on the pixel value of the virtual image. In this procedure, the watermarking information is embedded and a marked NURBS model is gotten. Experiment shows that the proposed method has the feature of transparency and robustness against the operations of knot insertion/removal, knot refinement, degree elevation/reduction, and affine transformations.Another new watermarking algorithm to embedding the watermarking information to grid model based on wavelet decomposition is presented. A series of the distance from the vertices of the grids to the center of the model is calculated firstly. Then, the vertices of the grids are grouped and decomposed with 1-D wavelet decomposition. After the watermarking information is embedded into its high frequency band, a marked new series is obtained with inverse wavelet transform. By adjusting the position of the vertices of grid model, a marked grid model is obtained.The grid-registration and grid-resample is needed before the watermarking extraction in this algorithm. Because the watermarking is embedded in the high frequency band after wavelet decomposition, and the embedded strategy of repeating embedded watermarking is also adopted, the algorithm has a good property of transparence as well as a better capacity against attacks.A series of digital watermarking simulation experiments and analyses are given for every algorithm in the dissertation. Some worthy conclusions are also gotten through analyzing the experimental results. The theory analyses and the experimental results show that the given algorithms are effective and they all have a good robustness and capacity against attacks.