@INPROCEEDINGS{Dondrup2014a,
  author = {C. Dondrup and N. Bellotto and M. Hanheide},
  title = {Social Distance Augmented Qualitative Trajectory Calculus for Human-Robot
  Spatial Interaction},
  booktitle = {Proc. of the 23rd IEEE Int. Symposium on Robot and Human Interactive
  Communication (Ro-Man)},
  year = {2014},
  pages = {519-524}
}