1. Introduction  
2. Differential Geometry Background  
2.1 Basic Prerequisites  
2.2 Curvature  
2.3 Covariant Derivative  
2.4 Laplace-Beltrami Operator  
2.5 Shape Operator  
3. Discrete Differential Geometry  
3.1 Voronoi Area  
3.2 Discrete Curvature  
3.3 Discrete Covariant Derivative  
3.4 Discrete Laplace-Beltrami Operator  
3.5 Isolines on Discrete Surfaces  
4. General Requirements of Feature Lines  
5. Feature Lines  
6. Discussion and Comparison  
6.1 Medical Application  
7. Conclusion