Algorithm 1: Spot extraction
Input: A trajectory T, δG, δD
Output: A spot sequence S
1:	i = 0, S = <>;
2:	while i < length (T) do
3:	j = i + 1, skipped = 0; lastIndex = i;
4:	sp = 〈pi〉; // start a new spot
5:	while j < length (T) do
6:	if skipped ≥ δG then // end of the current spot
7:	setStartEndTime(sp);
8:	S.Append(sp);
9:	break;
10:	else if dist(p; sp.c) ≤ δD then
11:	sp.Append(pj);
12:	lastIndex = lastIndex + 1; // reset the number of point skipped continuously
13:	else // the current point is consider as the noise
14:	skipped = skipped + 1;
15:	end if
16:	j = j + 1;
17:	end while
18:	i = lastIndex + 1;
19:	end while
20:	return S