Let me add comments for my question.
What I want to do ultimately is to check if a single tap XY point is near to pre-selected point(s). My current approach was to create envelope(s) from the pre-selected point(s), if this is possible, then check if the tap point is included in the envelope(s) by using .contains(Point p) method.
I would be very happy if there were any good ideas to realize what I want to do...
Thanks,
Gakumin