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What is an Aerial Photograph?
What is an Aerial Photograph?
Aerial photographs are images captured from an aircraft or drone, typically oriented perpendicular to the ground (nadir), and are fundamental to photogrammetry, the science of making measurements from photographs. In photogrammetry, these images are used to extract accurate spatial information such as distances, elevations, and 3D models of the Earth's surface. Key elements include the camera’s focal length, flight altitude, and ground control points (GCPs) for georeferencing. Overlapping photos enable stereo viewing, which is essential for creating topographic maps and digital elevation models (DEMs).
In the early days of photogrammetry, aerial photographs were taken using large-format film cameras mounted on aircraft. These cameras used high-resolution black-and-white or color film, typically with fixed focal lengths and precise timing mechanisms. The films were later developed in darkrooms and printed as contact prints or diapositives. Stereo pairs of overlapping photos were viewed using optical stereoscopes to interpret and measure terrain in 3D. Mapping was done manually using analog or mechanical plotters, relying heavily on skilled photogrammetrists. Accurate results required precise flight planning, stable aircraft, and well-placed ground control points.
Project Goal
Project Goal
The North Carolina Department of Transportation (NCDOT) and various municipalities, including our city, have historically contracted aerial photography projects to document infrastructure, land use, and development across the state. These aerial images, captured on film and dating back several decades, represent an invaluable visual archive of North Carolina’s evolving landscape.
The Engineering Department has launched a project to preserve and modernize this data. We are actively scanning the physical aerial film images that remain in our possession, while also leveraging already-digitized imagery available through NCDOT’s archival databases. This dual approach allows us to maximize the scope and continuity of the historical record.
Once digitized, the images are processed and georeferenced to create orthometric maps that are accurate and scaled representations of the Earth's surface that align with modern geographic coordinate systems. Through orthorectification, we correct distortions caused by camera angles and terrain elevation, resulting in maps that are reliable for spatial analysis, planning, and historical comparison.
Old aerial imagery is a valuable resource for understanding historical land use, environmental change, urban development, and infrastructure evolution. It provides a visual record of the landscape over time, allowing comparison with current conditions. These images support applications in planning, engineering, and environmental assessments. When processed with modern photogrammetry tools, historical imagery can be georeferenced and integrated into GIS, enabling accurate spatial analysis despite the age of the data.
The primary goal of this project is both preservation and public accessibility. By transforming fragile analog film into high-quality digital orthomosaics, we are ensuring that these historical resources are protected for future generations while making them accessible to researchers, planners, historians, and the general public. These maps will serve as a powerful tool for understanding how our communities have grown and changed over time.
Through this effort, we aim to honor the value of historical data while equipping today’s decision-makers and citizens with a meaningful view of the past.
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