This is a simple hack of the famous NUIGroups application used on multiTouch tables.
Camera input it´s replace for Kinect drivers (using Theo Watson´s addon: ofxKinect)
As Theo´s default example you can set the space between distance you want to track. And the you can apply any kind of filter (mous of the obsolet)
Just like the NUI app, you can calibrate the area and the send the position thought TUIO protocol.
In this video I´m using Memo´s MSA Fluid TUIO Demo from processing to show an example

http://github.com/patriciogonzalezvivo/KinectCoreVision