How Does Photogrammetry Work?

PHOTOGRAMMETRY

Photogrammetry is an essential part of our day-to-day lives. Though it is not something the average person may think of, photogrammetry is used in many ways, such as police work, sports, and map creation.

Photogrammetry is defined as the process of acquiring metric information about an object in a photograph through measurements made on that image. Photogrammetry software then allows users to create high-quality 2D and 3D models from these images that benefit manufacturing, forensics, public safety, and even video game production.

With so many great applications, how does photogrammetry actually work? At its core, it is the science of creating measurements from photographs or measuring the features within photographs, such as a mountain range. By flying above the mountains and taking photos every few meters, this software can then triangulate those points to create an incredibly accurate map of the mountains, including the distance between each point generated to scale.

Using Perspective Geometry

On a more technical side, photogrammetry is based on perspective geometry. Think of the camera lens as the perspective center. Light rays travel from a point in the photographed scene, through the perspective center (your lens), to the image of the point. To generate your map, drawing, measurement, or model, you will need to obtain images of the targeted point from multiple positions and locations.

Every point in a photo specifies a light ray in the 3D space. However, photogrammetry software needs additional information, such as the position and angles of the camera, as well as the focal length, pixel size, and lens distortion. Once all the necessary information is obtained, the software determines the geometric intersection of the light rays at various points in a process called point matching.

The process of using multiple photos to identify the distance between points is called triangulation. Through various algorithms, lines, surfaces, texture-maps, and 3D models can be generated from the accumulation of these points. You can also use photogrammetry on single photographs. When working to identify a robbery suspect, for instance, certain techniques can be used to determine their height from a single security camera frame.

The Essentials

For photogrammetry to be its most accurate, there are some essential components of the process. To start, the location of the photographs must be suitable for the work intended to be done. Aerial photography, land photography, and satellite photography are the most common types of photographs utilized in photogrammetry software. When taking these photos, you also want to consider the image quality, positioning and angles, and the field of view and overlap.

There are many advantages to using photogrammetry to develop maps drawings, measurements, and models. It quickly covers an area, is cost-effective, and illustrates incredible detail. The final result is something you can study from all sides to gather accurate data for surveys, manufacturing specifics, and generating special effects for film.

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