Aerial photogrammetry is a technique for creating two dimensional (2D) or three dimensional (3D) models from aerial photographs, which are pictures of the Earth from a high point, usually an airplane. These photographs are then turned into the models by cartographers. Aerial photogrammetry usually requires photographs of two or more angles of the same area in order to map the image, and it may or may not involve computer software.
For the most part, aerial photogrammetry is used to create topographical maps. These maps may be either 2D or, more recently, 3D computer models of terrain. The resulting maps and models may be useful in analyzing both small and large geographical areas. These maps may be used as a basis for, or in conjunction with, Geographic Information System (GIS) data.
Aerial photogrammetry may also be useful in a variety of industries. It is commonly used in architecture and land development. In addition, these mapping techniques may be used in environmental studies of a terrain, such as watershed or deforestation research, in city planning, or even in film production.
Most of the images used in aerial photogrammetry are obtained through cameras mounted to the undersides of airplanes. If the image needs to be taken from a low flight path, the camera is typically mounted to a small, remote-controlled airplane. Flight restrictions in many areas prohibit manned airplanes from flying too low over residential and business areas.
The flight pattern of the plane will typically meander back and forth over an area as the camera records the images. This pattern is meant to allow each area to be photographed from multiple angles. The aerial photogrammetry process almost always requires photographic data from multiple angles.
Photogrammetrists need multiple angles in order to determine the relative positions of objects in the photographs. This process is accomplished by isolating the same points in each photograph and triangulating their positions relative to each other. This process is typically accomplished with the help of a stereo-plotter, specialized computer software, or both. Stereo-plotters allow a cartographer to see two photographs simultaneously to better compare the points of interest.
In many cases the photographic data may not be enough to determine the full picture of the landscape. This may be especially true when creating a 3D landscape model. Therefore, aerial photogrammetry often combines other types of data with the photographs by using instruments such as Light Detection and Ranging (LiDAR), laser scanners, or white-light digitizers.