Photogrammetry

Photogrammetry is a specialized science and technology used to obtain reliable information about physical objects and environments.

It works by recording, measuring, and interpreting photographic images or patterns of electromagnetic radiant imagery. This process allows scientists to extract precise data from visual patterns. By analyzing these images, researchers can create detailed digital models of the real world. This technology is essential for understanding both small objects and massive landscapes. It turns simple light patterns into measurable, mathematical data.

The process involves several complex stages of digital image capturing and processing. To build a model, scientists must account for four main variables. First, they define the 3D coordinates, which are the specific locations of object points in space. Second, they identify image coordinates, which are the locations of those points on a film or electronic sensor. Third, they must establish the exterior orientation of the camera, which includes its position and view direction. Finally, they define the inner orientation, which involves the lens's focal length and any lens distortions.

To ensure these measurements are accurate, researchers use specific mathematical methods. One common technique is called stereophotogrammetry. This method estimates 3D coordinates by using two or more photographic images taken from different positions. Scientists identify common points that appear in every image. They then construct a line of sight, or a ray, from the camera location to the object point. The intersection of these rays is a process called triangulation. This intersection determines the exact three-dimensional location of the point.

Advanced algorithms help refine these models by minimizing errors. A common process is called bundle adjustment, which reduces the sum of the squares of errors across coordinates. This is often performed using the Levenberg–Marquardt algorithm. Researchers can also combine photogrammetry with other range data to improve accuracy. While photogrammetry is very accurate in the x and y directions, other tools like LiDAR are often more accurate in the z direction, or depth. By integrating these "point clouds" of data, scientists can create highly detailed 3D visualizations.

The history of this field shows how much our tools have evolved. The invention of the method is attributed to Aimé Laussedat. However, the specific term "photogrammetry" was coined by the German architect Albrecht Meydenbauer. He introduced the name in his 1867 article, "Die Photometrographie." In the early days, workers used stereoplotters to draw contour lines on topographic maps. Today, the field has expanded to include high-speed photography, remote sensing, and drone technology. These advancements allow us to measure complex 2D and 3D motion fields with increasing precision.

Photogrammetry has a massive range of practical applications across many industries. In filmmaking, it is used to combine live action with computer-generated imagery, as seen in the movie *The Matrix*. Video game developers also use it to create photorealistic environments, such as in *Star Wars Battlefront*. Archaeologists use it to map complex excavation sites or to study ancient Graeco-Roman funerary masks. Even meteorologists use this science to determine the wind speed of tornadoes when other weather data is unavailable.

In engineering and environmental science, the data is vital for safety and monitoring. Collision engineers use old police photographs to determine how much a vehicle was deformed in a crash. This helps them calculate the energy and velocity involved in the impact. In the marine sector, subsea photogrammetry allows for the inspection of offshore wind turbine foundations and underwater cables. It is also used to track environmental changes. For example, on Mount Stanley, drone photography and GNSS technology showed that a glacier's surface area declined by 29.5% between 2020 and 2024.