A Study On Watermark-based Copyright Protection For CAD Models

With the development of industrial design automation and computer network, the collaborative computer aided designing (CAD) in network environment has been increasingly becoming the choice of industry, and more and more of CAD models have been distributed via the internet. Online CAD issuing brings convenience to industry sector, while whom also been troubled by the problem of copyright piracy, that the data security has become one of the bottlenecks of CAD product release. In order to protect the copyright of CAD models, digital watermarking techniques have appeared.The current digital watermarking technologies almost aim at still images, video, audio and other traditional media types. The digital watermarking technologies of three-dimensional models are usually for three-dimensional mesh models still, while the CAD models in general are not based on mesh models, which can not use these methods to embed watermark information. Otherwise, the digital copyright programs for CAD models mostly have the robustness shortcomings or will result changes of the models' geometry when a watermark is. added into the model, or need the initial model to participate in the process of detecting the watermark. These disadvantages limit the digital watermarking of CAD models' applications.In this paper, a new approach of watermarking on CAD models for copyright protection based on chaotic map has been proposed. This method generates the watermark information to be embedded to CAD models by chaotic mapping, which effectively improves the anti-attack capability and the stability of copyright information in the CAD models; selecting target carriers by feature-based method, which chooses the most important features of CAD models as the embedded vector's target carrier of copyright information, resulting an expansion of the watermark information, and resisting the illegal users from stealing the copyright through tailoring the models; embedding the watermark information using relative knot insertion method, which completely maintain the topology and geometry characteristics of the CAD models so is suitable for the release of CAD products in the network environment.Based on this mechanism, a CAD models' copyright protection system is constructed. The system provides isomerism and robustness. Testing the related digital watermarking algorithms using this system, a high robustness, effectiveness and isomerism of the mechanism proposed in this paper have been shown.