Transition probability matrix generation:[[BR]]
1. convert timestamp to serial number and then sort[[BR]]
2. divide area into grids[[BR]]
3. loop: for each taxiid, find current grid & next grid, fill into grid matrix (row is current grid #, column is next grid #)[[BR]]
4. get prob matrix by normalizing grid matrix 

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Update generation:[[BR]]
1. divide updates into three different speed groups[[BR]]
2. in each speed group, set timestamp(poisson distribution) for each update[[BR]]
3. pick GUID (and its corresponding source AS) for each update randomly[[BR]]
4. compute destination AS (prob: how to match AS to grid in probability matrix)[[BR]]