A Hybrid Aggregate Index Method for Trajectory Data

Table 1

Bucket b_k eight-vector representation.

Vector	Description	Calculation/representation
Rk	The rectangular range of bucket bk	The coordinates of the upper left and right lower corners of bucket bk
nk	The number of cells in bucket bk	Integer representation
fk	Average frequency of cells in bucket bk
	Average square sum of cells’ frequency in bucket bk
	Average variance of frequency in bucket bk
mk	The number of sketches used in bucket bk	Calculate through the appropriate sketches method
skk	The number of moving objects in bucket bk	Exact value or sketch representation
lifespan[ts, te)	Lifespan of bucket bk	ts: the creation time of bucket bk; te: the update time of bucket bk