where is the kinect place to measure?

edit

You should measure from the Depth camera of the kinect. It is the middle camera in the kinect. If you are facing the kinect, the left one is the IR projector, the middle one is the IR receiver or the depth camera, the right one is the RGB camera or the normal camera we generally use in our project. If you can see the URDF of the Kinect, the frame which is been defined as kinect_depth_optical_frame, that is the frame, from where you should measure your distance.

Hope it helps.