A Context-Aware Location Differential Perturbation Scheme for Privacy-Aware Users in Mobile Environment

Algorithm 2

Hilbert value generation algorithm for each base cell.

Input: the T obtained from Algorithm 1, starting point and curve orientation θ

Output: a updated quad-tree root node T

initializes S(T) = , θ(T)= θ, m = 0;

push T into the stack;

while (stack is not empty) do

N = pop the top element from the stack

if (N has child node) then

for (i= sw, se, ne, nw) do

set S(N_i), and θ(N_i)

push N_i into the stack

end for

else

= m

set the values of all corresponding POIs in the node N as m

m = m + 1

end if

end while

outputs the updated quad-tree root node T.