@inproceedings{yu2007focal,
  title={Focal surfaces of discrete geometry},
  author={Yu, Jingyi and Yin, Xiaotian and Gu, Xianfeng and McMillan, Leonard and Gortler, Steven},
  booktitle={Proceedings of the Fifth Eurographics Symposium on Geometry Processing (SGP)},
  pages={23--32},
  year={2007}
}