Thursday, May 07, 2009

Lidar and Aerial Photos used to survey Ohio state

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, via press release.

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.

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.

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.

Lidar is a method of collecting highly accurate elevation data via an aircraft with mounted laser equipment. The data is accurate within plus or minus 1 foot in most terrain. Billions of lidar-generated points represent 3-D location/elevation data of terrain, waterways, roadways, buildings -- even tree cover.

"The imagery can be shown in 3-D and offers multiple views simply by rotating the images," said Brian Stevens, project manager for Woolpert. "Because the DEM data accurately maps the shape of land surface in three dimensions, it has many engineering uses beyond its primary purpose."

Ohio is one of the first states to create a seamless and highly accurate imagery data set, a blueprint for a larger goal of a seamless data set for the entire nation.


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