Algorithm 1. Modified region-growing algorithm

Input: Seed point (SD)

Output: Point set ($P_n$) Locate SD Check the eight neighboring points of the seed point, if their height compared to SD is smaller than that of the set threshold, $\delta$, add them to $P_n$ and $B_p$ Select a point, $B_i$, in $B_p$ and define its eight neighboring points as $T_i$. Check all of the points in $T_i$; if any point does not belong to $P_n$, and its height difference between $B_i$ is smaller than $\delta$, add it to $B_p$ and $P_n$. Erase $B_i$ from $B_p$. Loop process 3 to 5 until $B_p=\oslash$ Output $P_n$