@conference {spies2002e,
	title = {Estimating expansion rates from range data sequences},
	booktitle = {15th International Conference on Vision Interface},
	year = {2002},
	pages = {339 - 346},
	author = {Hagen Spies and John L. Barron}
}
@conference {spies2002,
	title = {Evaluating the range flow motion constraint.},
	booktitle = {ICPR},
	year = {2002},
	pages = {517--},
	author = {Hagen Spies and John L. Barron}
}
