Classifying Holes, Voids, Negative Objects and Nothing.

In the field of Urban Search and Rescue (USAR), searching for people trapped in the rubble of a collapsed building largely assumes the presence of many objects that are not the trapped victims, but may provide clues as to the location of them. However, the lack of objects can be just as informative. Unlike positive objects (POs), negative objects extend into the surface of interest [1], and may contain people. These negative objects (NOs) are commonly known as “holes” or “voids”.