Photogrammetric Engineers in the Photogrammetry Unit work with NCDOT's Project Managers to establish mapping requirements. This is done in early fall as part of the Photogrammetry Unit’s Annual
Requesting Mapping & Surveys
cycle since it is recommended to acquire all aerial photography between January to mid-April moving east to west across the state. The acquisition during this period is important because this is when the leaves are off the trees in NC. This yields higher ground visibility from all acquired aerial imagery resulting in more accurate mapping data. The most critical piece of information that is needed from the Project Manager is a project boundary because this tells the Photogrammetry Unit where to fly and what to map. Once the project boundaries are decided upon the purpose of the photogrammetric services must be discussed; preliminary design, final design, alternates selection, earthwork quantity determination, imagery for environmental purposes (color infrared), or imagery for planning purposes (Red-Blue-Green). Lastly, the mapping scale (ground sample distance) must be decided on because this dictates the flying height of the airplane.