Tech Notes
All About Aerial Mapping and Surveying
By Jon Weubben
Tue, 16 May 2006, 09:23 PST

Aerial mapping can be used to map the horizontal and vertical features of large areas of land in a more efficient manner than what is available by traditional survey methods. How does it work? Below are the following steps:

• A series of aerial photographs are taken and then used to create a stereoscopic image of the ground in a certain location.
• Each photo must have several points of known XYZ coordinates identifiable in the photo.
• These known points are used as the basis to create an accurate photographic model or digital terrain model of the subject area
• Accurate horizontal and vertical information can then be obtained from the photos.

What are the advantages over traditional survey methods? Aerial mapping and aerial photography can have increased efficiency in gathering large amounts of information, especially on larger sites. There are potential drawbacks however. These include:

• Features obscured by trees of other objects unidentifiable from aerial photos
• The possibility of less precise, though not necessarily less accurate, information than that obtained by traditional survey methods.

It’s important that all cameras meet National Aerial Photography Program (NAPP) specifications and are calibrated by the United States Geological Survey (USGS).

The Surveyor's Role

The surveyor plays a critical role in the aerial mapping process. They provide horizontal and vertical control for the mapping and they also provide supplemental information for the aerial mapping. Under the direction of an “aerial mapper”, the surveyor places aerial targets on the ground at positions that will provide adequate visual coverage for the photography. The surveyor will then provide the mapper with a list of coordinates and elevations for each aerial target. These are used as a control to set up the photographic model of the site. Supplemental information provided by the surveyor can include manholes, fire hydrants, or other items not visible by photo. In areas of critical match points, the surveyor may be able to provide information that is more precise than what is available by aerial mapping alone.

Other Important Things to Consider

• Some companies use of a combination of GPS for horizontal control and traditional methods for vertical control, which allows them to provide the accurate information needed to bring an aerial mapping project to a successful conclusion

• Camera systems/photography should be equipped with Forward Motion Compensation and low distortion, high resolution lenses. These aerial mapping cameras are designed for vertical aerial photography in a 9” x 9” format.

• Developing a flight plan helps to ensure the flight coverage encompasses the entire mapping boundary.

• Film should be processed immediately after the aerial photography has been flown.

• The photography should be edited and checked to verify that the specifications have been met. This allows any necessary re-flights to be done as soon as possible after the date of the original photography.

• During film editing it should be verified that the coverage was adequate and the photo scale was maintained throughout the flight.

• The film should be labeled so that contact prints and diapositives can be produced for use in the aerial triangulation, orthophotography, and mapping phases of the project.

Applications for Aerial Mapping and Surveying

Many people don’t realize all the different applications that use aerial mapping and surveying. These types of projects are all important to assisting in improved planning for cities, counties, companies and the government.

• GPS Surveys
• Topographic and Planimetric
• Above and below-ground utility surveys
• Geodetic control (horizontal and vertical)
• Differential GPS
• Analytical Aerotriangulation
• Topographic Surveys
• Volumetric Computations
• Manufacturing Plants - Stack Parameters for emission studies
• Planimetric Mapping
• Forest Inventories
• Cadastral Surveys Mapping
• Digital Terrain Model (DTM)
• Digital Elevation Model (DEM)
• Digital Orthophotography
• Utility Surveys
• Above and below-ground
• Airport Facility Mapping

Without aerial mapping and surveying companies; construction, municipal, and area planning would be less accurate and a lot more difficult, as well as more costly and time consuming.