Why is fingerprint-based indoor localization still so hard?

Brieuc Viel, Mikael Asplund. Why is fingerprint-based indoor localization still so hard?. In 2014 IEEE International Conference on Pervasive Computing and Communication Workshops, PerCom 2014 Workshops, Budapest, Hungary, March 24-28, 2014. pages 443-448, IEEE, 2014. [doi]