Ohio Uses Lidar and Aerial Photos to Survey State

The Ohio Statewide Imagery Program chooses lidar to make a highly accurate digital elevation model.

by / May 6, 2009

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.

Woolpert Inc., the Dayton, Ohio-headquartered engineering firm hired to do the aerial flyover, proposed a third alternative: Use lidar (light detection and ranging) to create a new, highly accurate DEM.

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.

"Lidar is a best-of-both-worlds technology. It's fast, accurate and the data has multiple uses," said Bob Brinkman, project director and senior vice president of Woolpert. "In terms of cost, it of course is more than free USGS data -- but using that data would have created unusable maps. On the other hand, lidar costs far less than the traditional surveying option."

The total cost for the flyovers and producing a complete data set: $5.5 million. The data set includes digital aerial imagery/ points, color digital orthophotography, color infrared (CIR) digital orthophotography and a lidar DEM.

"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."

Work began in 2006 and will be completed in 2009. Almost all of Ohio's 88 counties have now been flown, first capturing the aerial photos and then the lidar data. The same equipment has been used each time to ensure consistent data.

Subsequent field-survey checks have yielded results of two- to three-tenths of a foot vertical accuracy.

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.

Image: Lidar data can be used to produce 3-D, photo-like renderings.

Multiple Agencies, Many Users

Davis had a vision broader than his own: He wanted others -- whether employed by the state of Ohio or not -- to have access to the data. As the Ohio representative to the National States Geographic Information Council since 1997, he has seen at the ground level how seamless data could benefit many people -- and how combining resources could reduce redundancies and costs.

He fostered partnerships with members of the OGRIP Council, including representatives of Ohio's Office of Information Technology and departments of Transportation, Natural Resources and Development; the Ohio Environmental Protection Agency; USGS; local governments; and private-sector companies and academic institutions. OGRIP council members helped to shape the program's needs and also to champion the effort within their own agencies and among their own constituents.

"We collaborated at a council level and got buy-in upfront," Davis said. "We pooled our efforts and funding to achieve a greater goal, a higher level of shared product that benefited all, including the citizens of Ohio."

Each Ohio county was given the opportunity to "buy up" to even more accurate imagery resolution through a cooperative purchase agreement with the state. It's estimated that the collective cost savings to Ohio counties could total as much as $4.5 million, due in large part to the economies of scale realized through a statewide program and the fact that the state is controlling quality and costs. To date, 26 counties have opted for this higher-resolution imagery.

Williams County engineer Dennis M. Bell chose to upgrade when a study showed the time saved over field surveying would yield significant returns on investment. The county uses the imagery and data to identify problems in watersheds, plan for construction and maintenance of ditches, roads, and bridges; meet requests for survey data; and coordinate with the Federal Emergency Management Agency to update its floodplain maps.

Image: The Ohio Department of Transportation uses such cross-sections to plan roads and highways.

"Test surveys have verified the accuracy of the data, and not having to go into the field all the time has resulted in about 75 percent time-savings," Bell said.

Wayne County is also pleased with the data's accuracy. "The positional accuracy is spot-on with all of our other layers of data. The 'building lean' is near minimal, which is an upgrade to our older data," said Brian Hall, the GIS manager of the Wayne County Auditor's Office.

Dave Blackstone, GIS manager for the Ohio Department of Transportation (ODOT), said the lidar data alone -- not in combination with the aerial imagery -- is also being used. "When Ohio started the project, lidar was proposed as a means to an end -- to orthorectify and control the imagery. But the lidar data itself, and what it can be used for, is icing on the cake."

Blackstone said the lidar data is being used by ODOT engineers for a number of planning purposes, such as road and highway projects -- in some instances replacing traditional project preparation -- as well as flood prediction, appropriate sizing of bridges and culverts, and environmental impact studies. ODOT uses the homogenous imagery data set for road and crash analyses.


Image: This map of Findlay, Ohio, shows where flooding may occur in the city and other parts of Hancock County.

Mapping Natural Resources

The Ohio Department of Natural Resources (ODNR) uses lidar data to predict the impact of potential dam breaks and also to track defunct coalmines. An ODNR-led consortium pooled resources to

pay for the acquisition of 1-meter color infrared (CIR) imagery to create a homogenous CIR imagery data set being used for wetlands delineation.

The Huntington (Ohio) Corps of Engineers also uses the data for flood control projects as well as to conduct hydraulic and hydrologic modeling and stream-bank erosion studies in southeastern Ohio, Stevens noted.

Allen County uses the lidar data to produce contours that will in turn be used by the USGS to perform hydraulic and hydrologic studies of the county's streams.

According to Charley Hickman, USGS National Map liaison to Ohio, the agency is replacing its existing Ohio Quad Map-Based DEM with the new lidar DEM, providing a much higher level of accuracy for activities and projects taken on by the USGS and other federal agencies. For example, the OSIP data is being integrated into the National Elevation Dataset (NED), which provides bare-earth elevation data in a seamless "raster" format to the entire nation. All of OSIP's lidar point-cloud data will be integrated into USGS's Center for Lidar Information Coordination and Knowledge (CLICK), a national database for dissemination of LiDAR data for scientific needs.

Federal partners to USGS -- the U.S. departments of Homeland Security, Defense, Justice and Agriculture -- will use the OSIP data for urban line-of-site models, flood studies, terrain modeling, and new topographic maps and data.

The Ohio State Highway Patrol is downloading the data in order to conduct statistical analyses, said Christy Phillips, a GIS specialist in OSHP's Office of Strategic Services.

Jeff Smith, the OSIP project manager and the state of Ohio's spatial framework data manager in the Ohio Office of Information Technology's GIS Support Center, said it's not just government agencies using the data. "The private sector is eating this up -- we've provided data to dozens of private firms and individuals -- from tree trimmers and landscape designers for site evaluation and design -- to academics and engineers doing predictive modeling and project plans for land development."

Molly Klimas Contributing Writer
Molly Klimas is a writer based in Grand Rapids, Mich.