By observing situations in real life, we could say that owners usually carry on their objects to AbandonedOb- jectArea, could be stand or step around for a while, then totally leave that area. Therefore, we define two terms for marking the period when owners start and finish leaving their object (KeyTime): (1) appearance time (Tapp): is the time objects totally appear in AbandonedObjectArea, and (2) start-appearance time (Tstartapp): is the time objects just start appearing in AbandonedObjectArea. It should be noted that Tstartapp ≤ Tapp. In other words, when owners carried on their objects approach AbandonedObjectArea, we mark that moment by Tstartapp; and when objects totally appear in AbandonedObjectArea, we mark that moment by Tapp. Therefore, KeyTime = [Tstartapp, Tapp].