CAD drawing watermarking scheme

A CAD (computer-aided design) drawing based on vector data is very important art work in industrial fields. It is considered to be content for which copyright protection is urgently required. This paper presents a watermarking scheme based on k-means++ for CAD drawings. A CAD drawing consists of several layers, and each layer consists of various geometric objects such as LINE, POLYLINE, CIRCLE, ARC, 3DFACE, and POLYGON. POLYLINE along with LINE, 3DFACE, and ARC objects are the most commonly used fundamental objects in a CAD drawing. The proposed scheme embeds the watermark into the geometric distribution of POLYLINE, 3DFACE, and ARC objects in the main layers. Hence, in the proposed scheme, we select the target object with a high distribution among POLYLINE, 3DFACE, and ARC objects in a CAD drawing and then select layers that include the maximum number of instances of the target object. Then, we cluster the target objects in the selected layers by using k-means++ and embed the watermark into the geometric distribution of each group. The geometric distribution is the normalized length distribution in a POLYLINE object, the normalized area distribution in a 3DFACE object, and the angle distribution in an ARC object. Experimental results have verified that the proposed scheme is robust against file format conversion, layer attacks, and various types of geometric editing carried out using the CAD editing tools.