10. In a computing environment, a system comprising: a general purpose computing device; a computer program comprising program modules executable by the general purpose computing device, comprising: an insertion logic module that builds compressed start-end trees from sets of GPS data; a search logic module that searches among compressed start-end trees to find one or more tracks corresponding to a subset of GPS data that match a spatio-temporal input request; and compression logic that converts at least one of the compressed start-end trees from one data structure type to another based on a likelihood of each compressed start-end tree being updated according to subsequently-received GPS data.
10. In a computing environment, a system comprising: a general purpose computing device; a computer program comprising program modules executable by the general purpose computing device, comprising: an insertion logic module that builds compressed start-end trees from sets of GPS data; a search logic module that searches among compressed start-end trees to find one or more tracks corresponding to a subset of GPS data that match a spatio-temporal input request; and compression logic that converts at least one of the compressed start-end trees from one data structure type to another based on a likelihood of each compressed start-end tree being updated according to subsequently-received GPS data. 13. The system of claim 10 wherein the insertion mechanism determines segments of a track according to spatially partitioned cells, and for each segment, inserts start and end time data representative of that segment into a particular compressed start-end tree associated with the cell corresponding to that segment.