May 6, 2009 By Molly Klimas
Fly over Ohio at 30,000 feet and its cities and counties -- like much of the Midwest -- look like a patchwork quilt.
Until recently, so did imagery and GIS data across the state.
But information that was once "stitched together" is now seamless, thanks to a multiagency effort called the Ohio Statewide Imagery Program (OSIP). The program's data is making government technology professionals' jobs more efficient and their work far more precise.
"It's complete and accurate data that anyone can access for mapping, engineering and planning," said Stu Davis, executive director of the Ohio Office of Information Technology's Ohio Geographically Referenced Information Program (OGRIP) -- the agency that spearheaded OSIP.
In 2006, the state decided to replace its decade-old, 1-meter black-and-white aerial photos with high-resolution digital color imagery. But the imagery would need to be orthorectified (corrected for surface elevation changes) in order to truly be usable as maps depicting accurate distances.
Davis had a problem. He needed a highly accurate digital elevation model (DEM) over which the imagery would be "draped" to orthorectify the imagery. The existing DEM -- the U.S. Geological Survey's (USGS) National Elevation Dataset, spaced points at 30 meters apart -- hardly provided the accuracy needed.
"A lot can vary within 30 meters," Davis said. "The USGS DEMs still have value, but not for 21st-century state and local government requirements. To have used the existing DEM would have created a throwaway product."
One alternative would have been to compile a new DEM of the entire state using traditional methods of surveying and photogrammetry (determining geometric data from photographs). But these methods are often time- and cost-prohibitive.
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