From a Historical Lens
Digital photogrammetry is as recent as the1980s. However, centuries ago, in 1480, Italian Renaissance artist and inventor Leonardo da Vinci had postulated his theory of incorporating perspective into illustrations, that vanishing points must appear smaller, while the objects that grow out of them larger since these objects are meant to be closer to the eye.
Aimé Laussedat, a French scientist, indicated in the 1850s that photography was a resource for mapping. He is often considered the “father of photogrammetry.” As the practical uses of photogrammetry grew in recognition, experimentation with the technology grew during World Wars I and II.
The 20th century witnessed advancements in the field, particularly in analytical photogrammetry, which allowed computers to solve complex mathematics, thanks to Uki Helava in the 1950s. The early 1990s brought digital cameras into the picture, leading to both imaging and computations being done digitally. Now, photogrammetry software is available worldwide. Aided by sophisticated instruments, the latter half of the 20th century boasts of developments such as satellite photography, very large-scale photographs, automatic visual scanning, high-quality colour photographs, and the use of films sensitive to radiations beyond the visible spectrum and numerical photogrammetry.
Breaking It Down
The word ‘photogrammetry’ is somewhat of a mouthful but easier to understand by breaking it up into its components. “Photo” means “light”, “gram” denotes “drawing”, and “metry” stands for “measurement”. Thus, photogrammetry is a technique that uses photographs to carry out measurement.
What’s Cool About It?
Using photogrammetry techniques, you can capture gigantic objects, such as mountains, buildings, and volcanoes, which fall outside the scope of other scanning methods. What’s more, the equipment you need is likely at hand - it could just be the camera on your smartphone. Add to your toolkit appropriate photogrammetry software from the diverse choices available, and you have all that you need to generate a 3D file of the object you caught on your camera. The 3D models allow you to examine scaled, detailed scenes of the areas you photographed from all the right angles and all on your computer screen.
How Does It Work?
Imagine that you wish to chart a section of a mountain range. You would fly above the area, clicking a picture at short distances, such as every few metres. With the photographs in place, you would use photogrammetry software to triangulate each point photographed and create a precise 2D or 3D map of the section, generating the inter-point distance to scale.
“Point matching” is the process of finding two or more points on the photos that correspond to the exact 3D location. You can do this manually or automatically. “Ray intersection” refers to the meeting up of light rays. The overall method of using multiple photos for solving points is called “triangulation”.
Types of Photogrammetry
In addition to the standard aerial and terrestrial photogrammetry, there is also the satellite version based on photos taken in space from an orbiting satellite. Typically, such images are helpful for governments to triangulate points on large portions of the earth. This type of photogrammetric location also is a typical source of data for Google Earth and Google Maps.
Where Is It Used?
From surveying and mining to forensic photography and manufacturing, you could apply your skills in various settings and to diverse objects. Ecological studies and forestry also benefit from photogrammetry. You could even use the techniques for single photographs, for instance, to determine the height of a burglary suspect in a single frame from a security camera, with additional data about the scene.
Use in Cartography
Following wartime usage, photogrammetry evolved immensely in its peacetime applications. Today, it is a salient tool in cartography or mapmaking, particularly to map inaccessible areas. An advantage of aerial views is that special cameras can capture large areas in totality, minimising the chances of blind spots that may escape the lens of a terrestrial camera.