@article{yan2016position,
  title={Position-Normal Distributions for Efficient Rendering of Specular Microstructure},
  author={Yan, Ling-Qi and Ha{\v{s}}an, Milo{\v{s}} and Marschner, Steve and Ramamoorthi, Ravi},
  journal={ACM Transactions on Graphics (Proceedings of SIGGRAPH 2016)},
  year={2016},
  volume={35},
  number={4}
}