Watermarking scheme for geometric data protection and detection on 3D CAD assembly model

ÂNowadays, different contemporary products are modeled in a CAD environment. These involve a number of components and assembled together to form an assembly model. Such related components of a product are assembled by different mating conditions in a product design and development stage. Normally, the assembly model would be distributed to different staffs or personnel involved in the process. To ensure that the assembly model received is an original one and is not altered by any unauthorized persons during transmission and exchange of files on the internet, watermarks should be embedded into the model nowadays. In this paper, a watermarking scheme is proposed specifically for watermarking the assembly model structure and the positions and orientations of the components. In this proposed scheme, unique component ID number is assigned to each component. For each component, a hash value is calculated based on the ID numbers of the components related to it in the assembly model tree structure. By detecting the hash value, any change or update in the tree structure can be detected. To watermark a component’s position and orientation, some points on a component are first selected. While keeping the selected points on the corresponding component, watermarks and hash values are embedded into the coordinates of the selected points using specified keys by changing the values of the coordinates slightly. The coordinates of the selected points are then stored in the attribute properties of the corresponding component. To detect whether a component’s position or orientation are altered, the selected points must be checked and verified whether they are still on the component. In case some of the points are not on the component, the position or orientation of the component is considered as altered. If all the points are still on the components, the watermarks and hash values must be extracted in order to detect whether the watermarks are attacked. Based on the proposed scheme, any unauthorized changes or intended attacks on the watermarked information of an assembly model can be detected. The geometric data and information of the components for the original 3D assembly model can be protected.