By efficiently extracting topological and geometric features regardless of their heterogeneity with respect to geometrical shape and topology representation, the proposed framework supports verifying topology integrity for various heterogeneous engineering CAD drawings, such as process flow diagrams (PFD), piping and instrument drawings (P&ID), piping isometric drawings (ISO) as well as sectional drawings. However, topology integrity authentication for engineering CAD drawings is still in its infancy and few efforts were made in the literature. Topology information, through which a variety of engineering reports are generated, plays the most important role in the engineering CAD field. This paper presents a novel unified framework for authenticating topology integrity of 2D heterogeneous engineering CAD drawings. The proposed scheme can be employed to authenticate topology integrity for each of the drawings derived from the model individually in industry practices.

Theoretical analysis and experimental results demonstrate that our approach yields a strong ability in detecting and locating unauthorized topology attacks while achieves robustness against both global and local similarity transformations especially the stretching operation. These generated topology sensitive watermarks are embedded into geometrical invariants of each node via quantization index modulation. After that, the topological relation among joint components is encoded into singular watermarks for each node of the graph.

Then, similarity transformation invariants are constructed as watermarks carriers for each node. The topological graph is extracted and constructed from the drawing firstly. In addition to the stretching operation, both global and local similarity transformation operations, which are critical problems in the case of watermarking embedding and extraction, are analyzed in detail. The topology authentication problem of piping isometric drawings is investigated. A blind and semi-fragile watermarking based algorithm is proposed to address the referred interesting issue.

This paper takes a fresh look at the topology integrity authentication of piping isometric drawings, which has not been mentioned before in the literature, from the digital watermarking perspective. Piping isometric drawings, which feature their intrinsical topological relation rather than just geometrical shape, are important industrial art works in the field of Computer-Aided Design (CAD).

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