indexforcitytrajectories-wenkub
2022-10-29 01:48:44 本頁面
【正文】 icient retrieval of trajectory for a small number of moving objects. ? SEBtree ? Range query ? Time slice query Number of moving objects Processing strategy Small TBtree Large Rtree MONTree index ? The index structure consists of three ponents: ? a 2D RTree (the top RTree) ? indexing polyline bounding boxes ? a set of 2D RTrees (the bottom RTrees) ? indexing objects’ movements along the polylines. ? a hash structure in the top level containing entries of the form hpolyid, bottreepti, The hash structure is anized by polyid. ? polyidis the polyline identification ? bottreept is a pointer to the corresponding bottom RTree. ? Hence, we have two top level index structures: an RTree and a hash structure MONTree index (cont.) SEBtree (Start/End time stamp Btree) (MDM2020) ? Suppose n is the population of objects. In zone z, after a period of time, N tuples, which include both the current status records and the history records, are generated. There is at most one current status record for each object, therefore, at most n among N records could be the current status record, where n format of each tuple is (id, z, ts, te). Since all records have identical zoneids, we omit field z. Now each tuple has three fields (id, ts, te), where ts maximum number of records that can be stored in one disk page is B. ? An interesting property about the history records is that the tuples are sorted by their end time stamps, To index the history records, the first step is to construct a 2dimensional space where the start time stamp and the end time stamp are the horizontal and the vertical axes. Each record are mapped to a point in the space. Since in each record ts te, the points are all in upperleft half of the plane. ? Three steps are executed when we insert a new point: 1) check the start stamp list and find the column where the point is inserted。 0101Group moving objects Previous approach –TPRtree ( t interval ) Previous approach –TPRtree ( t+1 interval )
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