Digital photogrammetry uses computers to measure objects in photographs or videos. It requires information about the camera used and the desired size of measurements, and can use aerial or close-up photography to create 2D or 3D models. It has applications in various industries such as architecture, manufacturing, and police investigations.
Broadly speaking, digital photogrammetry is the art of using computers to obtain measurements of objects in a photograph. It typically involves analyzing one or more existing photographs or videos with photogrammetric software to determine spatial relationships. While commonly used to create topographic maps, it can also be useful in a variety of industries such as architecture, manufacturing, police investigations, and even plastic surgery.
There are several important variables involved in digital photogrammetry. First, it can be useful for a photogrammetrist to know information about the camera, such as the type of camera that took the photo, the focal length of the lens, or the camera’s distance from the object of interest. A special type of camera, called a metric camera, is often used to take these photographs because it is calibrated to take precision photographs with little lens distortion.
A second variable to consider in digital photogrammetry is the desired size of the measurements. Some projects only require two-dimensional (2D) measurements, such as the height of a building or the width of a river. These measurements can be made from a single photograph. If, however, the measurements are to be three-dimensional (3D), the process typically involves creating a 3D model from two or more photographs.
This process of creating a 3D model is usually called digital stereophotogrammetry. Stereophotogrammetrists usually analyze two or more photographs of the same object, taken from different angles. They typically use the space where the photographs overlap or common landmarks shared by the photographs to create a digital 3D model. The images can then be mapped, pixel by pixel within the model to create a measurable space in three dimensions.
A third variable is the type of photographs used. Photogrammetrists usually use digital still photography or video. Film photographs and videotapes typically need to be scanned into a computer for use in digital photogrammetry.
The two main categories of photography are aerial and close-up. Aerial digital photogrammetry, often used in topographic mapping, begins with digital photographs or video taken by a camera mounted on the bottom of an airplane. The aircraft often flies over the area in a tortuous flight path, and then may take overlaid photographs or video of the entire area to get complete coverage.
Digital close-range, or terrestrial, photogrammetry often uses photographs taken at close range with handheld or tripod-mounted cameras. Close-up photographs can be used to create 3D models, but are not usually used in topographic mapping. This type of photogrammetry is useful for 3D modeling of many objects or areas such as buildings, car crash scenes, or movie sets.
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