Building-change survey from two aerial photos

Building additions are hard to spot on patrol: they sit in back yards, on rooftops and behind facades. An inspection department needs a list of places worth checking, not another general patrol.

We coded every building on two aerial photos from different years and compared them. New buildings, demolished buildings and footprints that grew beyond a threshold agreed with the authority were marked in a change layer. Oblique imagery was used to check added floors, balconies and extensions that cannot be seen from above. Each suspected case got a screenshot, and the findings were compiled in a report by priority.

The inspection department goes out with a sorted list and an image for every finding, and can cross-check it against permit records to focus on additions that were never approved.