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GCN : April 2013
FEATURE 3-D DATA GATHERING GCN APRIL 2013 • GCN.COM 23 Using a robotic LIDAR platform, the city of Philadelphia created a dataset of building interiors that included CAD, 3D an video models of the structures and their contents, including stairways, doors and even furniture. Philadelphia has long been at the cutting edge of GIS. And a recent pilot project that employed LIDAR-collecting robots has convinced even the city s skeptical GIS director of the value of moving beyond 2D maps to the 3D models that LIDAR enables. In 2008, the city decided to use some available grant money to launch a project to scan its Center City area with LIDAR and combine it with existing oblique imagery data. Oblique imagery is aerial photography captured at an angle that shows the top and sides of objects. "It was purely experimental," said GIS director James Querry. "We decided to apply it to a section of the downtown and a section of a sports complex area and see what happened. Up to that point I was not convinced that 3D modeling was a viable solution for anything as it was so expensive to create any meaningful level of detail." Two factors changed Querry s mind. First, "I found out that we could generate a model from data that we already collect for other things: oblique imagery." The city had been generating aerial oblique imagery since about 2003 to have a record of changes in the city s urban infrastructure. The imagery was already in use in departments across the city for such things as zoning applications, asset management and emergency response. According to Querry, aerial LIDAR data helps his sta generate digital elevation models that can support the correction of aerial imagery. The second factor was the demonstrated value of collecting not just above-ground data from aircraft, but interior data -- the insides of buildings and underground structures. In 2010, the city had a contractor scan the insides of selected public buildings and the underground transportation infrastructure. A robotic LIDAR platform was pushed through the halls, rooms, tunnels and other spaces at a human s walking pace, collecting more than 5,000 data points per square meter. The robot also took 360-degree geo-referenced images. The result was a dataset that included both CAD and 3D models, including video models, of the structures and their contents, including stairways, doors and even furniture. "We re collecting everything from building fa ades to polls and trees," said Querry. "Even doorknobs." The potential demonstrated by the pilot, Querry says, was impressive. "For major buildings and underground spaces where people congregate, you have a fully geo-referenced and fully intelligent 3D model, showing doors, access ports, escalators, stairs, even down to a ladder that is actually an emergency access," he said. "There are a lot of things you could use this fully intelligent 3D model for," he added. "Public safety and emergency management are probably at the top of the list. If something happened in one of the subway areas and you re sending first responders in in those first responders have transponders, you can see where they are in the model and you can help guide them." Querry says that despite the promising performance of the model, more needs to be done. "We re at the point where the technology has been tested and it is evolved a bit on the data collection side and the software side. I think we re at the point now where if we wanted to do that we could," he said. "It s totally function of resources." --- Patrick Marshall THE FUTURE: URBAN LIDAR MAPPING