In general, digital photogrammetry is the art of using computers to obtain measurements of objects in a photograph. It typically involves analyzing one or more existing photos or videos with photogrammetric software to determine spatial relationships. While it’s commonly used to create topographical maps, it can also be useful in a variety of industries, including architecture, manufacturing, police investigation, and even plastic surgery.
Photogrammetry is the process of constructing scale maps or drawings from aerial photographs or other relevant images.
There are several important variables involved in digital photogrammetry. First, it can be helpful for a photogrammetrist to know information about the camera, such as what type of camera took the picture, the focal length of the lens, or the distance from the camera to the object of interest. A special type of camera, called a metric camera, is often used to take these photos because it is calibrated to take precision photos with little lens distortion.
Digital aerial photogrammetry, often used in topographic mapping, begins with digital photos or video taken from the bottom of an aircraft.
A second variable to consider in digital photogrammetry is the desired dimensions 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. However, if the measurements need to be three-dimensional (3D), the process usually involves creating a 3D model from two or more photographs.
This process of creating a 3D model is commonly called digital stereophotogrammetry. Stereophotogrammetrists often analyze two or more photographs of the same object, taken from different angles. They typically use the space where the photos overlap or common landmarks shared by the photos 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 photography used. Photogrammetrists often use digital photos or video. Film and videotape photographs generally need to be digitized on a computer for use in digital photogrammetry.
The two main categories of photography are aerial and close-up. Digital aerial photogrammetry, often used in topographic mapping, begins with digital photos or video taken from a camera mounted on the bottom of an aircraft. The aircraft will often fly over the area in a winding flight path so you can take photos or overlay video of the entire area for complete coverage.
Short-range or terrestrial digital photogrammetry often uses photographs taken up close with handheld or tripod-mounted cameras. Close-up photos can be used to create 3D models, but are not generally used in topographic mapping. This type of photogrammetry is useful for 3D modeling of many objects or areas, such as buildings, car accident scenes, or movie sets.
