Algorithm 2. The CP Determination for Tracking Multiple Targets.

Initialization: Get the coordinates of all wireless sensor nodes, as well as topology information of all LOSLs. Step 1. Decide the number of targets by triggering LOSL in separated zones   if the targets do not meet at the neighbor regions.    Step 2. Divide the triggering LOSLs into groups belonging to different targets.    Step 3.  Individually perform tracking work on each target by using the geometric constraint method presented in Algorithm 1;    Step 4.  List all the possible explanations when multiple targets are triggering the same LOSL and conflict occurs.    Step 5.  Further adopt the later trigging LOSL measurements to eliminate the other possible explanations to get the unique solution.   else     Give warning sign and increase the LOSL density to solve the meeting event.   end