With the coming of the 3D digital media age, there will emerge more and more 3D models both on the Internet and in industry. As the 3D models are increasing rapidly, how to quickly search desired 3D models and reuse existing models is becoming an important research topic across multiple research fields and applications. Sketch-based 3D model retrieval is one of the most promising techniques among 3D model retrieval methods because of the nature of sketching, which appears to be an intuitive communication method in Human-Computer-Interaction. Currently, there are two main problems unsolved in e...