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AIRBORNE
Mission Possible
Navigation system combines with aerial photography
for unintrusive mapping mission at Hartsfield International Airport
By Irving C. Hoffman Challenging was an understatement. The mission was new aerial photography and mapping of one of the nation's busiest airports - Hartsfield Atlanta International Airport. This airport serves over 60 million passengers annually, and averages well over 2,000 takeoffs and landings each day. Just acquiring aerial photography at such a heavily trafficked facility seemed nearly impossible.
In February of 1997 Hoffman & Company, Inc. (HCI) was awarded a contract for "aerial photography and 3-D database development" of the airport and surrounding property. HCI's client, Aviation Consulting Engineers (ACE), is a joint venture of Williams-Russell and Johnson, Inc.; Bechtel Corporation; and Delon Hampton & Associates, Chartered. ACE serves the city of Atlanta's Department of Aviation as its engineering and design consultants. The overall goal of this project was to produce a digital database that would meet the airport's master planning and design needs for improvements and expansions. By using the latest in aerial survey and photogrammetric technologies, HCI gave ACE a digital solution that functioned in a variety of formats for anyone who may need the data. Aerial Photography
The first major challenge was acquiring the photography. Using a combination of airborne GPS, HCI's on-board flight navigation system, and minimal GPS ground control, HCI was able to complete the flight mission and control within seven days of notice-to-proceed. This photography was acquired in three flights - one for the 1:40,000 scale color photography, one for the 1:20,000 scale, and one for the 1:8400 scale black & white photography.
Coordinating carefully with the Federal Aviation Administration (FAA) and air traffic controllers at Hartsfield, HCI used their CCNS4 - Computer-Controlled Navigation System, which allows the flight crew to pre-program the flight plan into the on-board computer. The CCNS allows the camera exposures to be automatically fired at the precise location desired, as indicated by the airborne GPS equipment. "We could have never done this project without CCNS," states Mike Rowell, manager of aerial photography at HCI, "getting the photography the first time was critical to this project. We had assured the air traffic controllers that we'd be in and out of there in a day. They were impressed that our disruption was so minimal." Rowell commented.
HCI used a Leica 9500 GPS unit as their airborne receiver, from which they were able to quickly download data assuring that the flight mission objectives had been met. Ground crews adjusted the system to six existing FAA monuments that were tied to both the NAD83/95 High Accuracy Reference Network (HARN) and the airport's grid coordinate system. Mapping
The base mapping effort involved 13,500 acres at 1" = 100' scale, with 2-foot contours. In such a large mapping effort, making the data as flexible and manageable as possible was the major consideration. Because Fulton County, Georgia, and other counties and cities surrounding the airport either have existing or are in the process of constructing Geographic Information System (GIS) databases, HCI felt it was important to make this new data compatible with these GISs. With agreement from ACE, HCI delivered the data in both the airport's existing grid coordinate system, and the state plane coordinate system, (the "nested" tiling system used for these GISs, as recommended by the state of Georgia's GIS Advisory Committee). All the digital terrain models (DTMs) were delivered in both AutoCAD and MicroStation formats, to provide the greatest flexibility and compatibility in using these data within other systems.
The project schedule was aggressive, calling for all mapping and 3-D wireframe data to be provided within seven months of notice-to-proceed. HCI subcontracted with Photo Science, Inc. of Lexington, Kentucky, and Southern Resources Mapping of Miami, Florida, for additional mapping and 3-D capabilities and capacity. The immediate 7,000 acres of airport facilities were digitally compiled as 3-D wireframe objects by Photo Science, with an outstanding level of detail on roof, building and surface utility features. The remaining 6,500 acres surrounding the airport were compiled as a 3-D map file, but did not require additional wireframe structures. However, because the height of the trees, building, and other structures was critical, HCI used spot elevations placed at the high point elevation. From this, wooded areas were outlined at 70% average height, and spot elevations were scattered throughout at the high points.
The scope also called for color enlargements at 1" = 300', 1" = 600' and 1" = 1000' of an area covering roughly 17 x 7.5 miles. Instead of traditional photographic laboratory processes, HCI produced the enlargements digitally, using their Zeiss SCAI photogrammetric quality scanner, again providing more potential uses for this photography. The real challenge came with the 1" = 1000' mosaic, which is comprised of 27 separate photographs. Since this mosaic would be used specifically for public display, a simple mosaic with all inherent scale distortions would not do. HCI opted to ortho-rectify the 27 photographs to create a seamless mosaic that looks like a single photograph.
Having these digital orthophotos readily available proved valuable in an unexpected way. ACE was able to use the digital orthos immediately to design 2,000 additional parking spaces prior to the heavy passenger traffic during Thanksgiving 1997. Uses of Data
In the five months since the mapping and digital orthophotographs have been delivered, ACE and the city of Atlanta's Department of Aviation have found many uses for the data. ACE is currently using the data files to render conceptual designs of structures for airport expansion and improvements. Using the digital files, engineers at ACE have been able to model a planned taxiway that will also serve as a temporary runway during upcoming maintenance. "We used the data files in our system to create obliques and show the airlines that this taxiway will indeed function just like a runway during the repair time, which answered the concerns they had about this issue," explains Bill Steffen, project manager with ACE.
The Department of Aviation overlays various alternate master plans over the digital orthos for public meetings and other informational uses. They are currently in the process of using the wireframes and other data to prepare 3-D models of the various master plan alternatives. Having the orthophotos as a base for the AutoCAD overlays is extremely useful to the planners and others providing input to the master plan. They can see much more clearly the impact of various expansion scenarios on the surrounding neighborhoods and businesses.
In a relatively short time, these data have been used in many ways. The topographic data are routinely used in line- of-site studies. The marketing/public relations department has even used the aerial photography as graphics on its new Web site, and has plans to use the photographs in several marketing pieces. Conclusion
By using the latest in airborne GPS and flight management technology, Hoffman & Company, Inc. of Smyrna, Georgia, was not only able to acquire and produce high quality photography, but was recently awarded an Engineering Excellence Award by the Georgia Consulting Engineers Council for the project's contribution to the engineering community in Georgia. The project has been submitted in the Surveying & Mapping category of the American Consulting Engineers Council (ACEC) national Engineering Excellence competition. This is the first year that ACEC's competition has had a separate category for Surveying & Mapping projects, recognizing the increase in technology and innovation in this field and the ability of firms specializing in these areas to have a positive impact on the engineering profession. About the Author:
Irv Hoffman founded Hoffman & Company, Inc., a photogrammetry, aerial photography and surveying firm in the Atlanta, Georgia metro area, in 1969. Mr. Hoffman has over 35 years of surveying and mapping experience.
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