The threat of bushfires looms large in southern Australia. An airborne vision system under development may make prevention easier by targeting one of the leading causes of fire: contact between power lines and tree branches in the bush. Contact between tree branches and power lines is a leading cause of bushfires in southern Australia. An airborne vision system that reconstructs the terrain in three dimensions may enable power companies to better monitor tree clearance. Powercor Australia, the largest electricity distributor in Victoria, annually invests millions of dollars and thousands of man-hours in the manual inspection of power lines, many in rural areas. The company wanted a more efficient, less costly approach, so it enlisted the Commonwealth Scientific and Industrial Research Organisation, the country's national science agency, to create an airborne 3-D imaging system that can automatically inspect the lines. A survey company collected sample images over western Victoria with an aircraft that it had fitted with a standard video camera under each wing. The streams of images were collected and converted into digital format, and the agency's Image Analysis Group used proprietary stereo-matching and object-recognition software to distinguish among power lines, poles and the surfaces of trees. "This technology is a form of stereo vision," explained Mark Berman, an imaging specialist who worked on the project. By using a sequence of stereo image pairs of a given scene, the system automatically reconstructs three-dimensional representations of the scene and measures distances. Because of the vast regions of the Australian outback to be inspected, Berman estimates that the system must cover 500 km in a six-hour flight. This corresponds to 25,000 images per camera over that time, translating to a capture rate of 1.16 seconds per image. Researchers at work The imaging system is still in the prototype stage, and the group is seeking partners to share the cost of its development. "In order to make the system operational, we need to use higher-resolution digital cameras, which will enable us to identify objects more reliably and to make more accurate measurements," Berman said. "This will cost quite a lot of money." He predicts that the system will have other uses in similar "corridor-mapping" applications, such as in telephone-line maintenance and in the surveillance of oil, gas and water pipelines. "The stereo-matching part would essentially remain unchanged," he said. "However, the object-recognition components would need to be tailored to the particular application."