Since the first photograph was taken by Joseph Nicéphore Niépce in 1826 photography and cameras have changed dramatically over the years. Now taking a picture is as simple as pressing or tapping a button on a mobile phone. But there is a whole different side to photography most of us don’t know: Photogrammetry. What’s this word? What does it mean? Is it the same as photography? Who uses this? Well, let’s start at the beginning.
The word “Photogrammetry” is derived from three Greek words: phos or phot, meaning light; gramma, which means “letter” or something drawn and metrein, the noun of measure. This word was first introduced in 1867 by German geographer Otto Kersten. The word “Photogrammetry” means the process of making surveys and maps using photographs. It is the art, the science, the technology of obtaining reliable information and measurements about the properties of surfaces and objects through photographs.
Photogrammetry is not photography. Photography uses cameras to get the final output. Photogrammetry uses photographs to get the final output. With that said, comes the question of “what is photogrammetry then?” Photogrammetry has many techniques, but the key methods are optical and projective geography methods.
In projective geography, we use special software to detect similar points in photographs and align them. This software extracts three-dimensional data from two-dimensional images. The distance between two points on a plane parallel to the image plane can be determined by measuring their distance on the image. Also, it extracts colour data from the images representing diffuse, specular, ambient occlusion and metallicity so that the re-creation can be textured as an ultra-realistic model. Imagine you need to model an old statue in your city centre. To do this, first you have to take a couple of dozen overlapping photographs in an orbital manner either from top to bottom or circling the statue with the camera in different heights. Thus, you get rings of photographs. By taking overlapping photographs, it’s easier to triangulate a specific point and calculate the distance between objects in the photos.
The other method is the use of optical scanners. A 3D scanner is a device that uses infra-red light beams to construct metric data from objects it is scanning. Laser scanners gather plane data using a laser beam pointed at the surface and then converting that data into a point cloud. These point clouds are made with software like Agisoft Metashape, Reality Capture and Autodesk ReCap to make life easier through the pipeline.
The outcome of laser scans is more accurate than photographs. This is because sometimes in photogrammetry reconstructing smooth, transparent or reflective objects is a bit tricky. It’s hard to identify details of those kinds of objects since there’s no point to grab on to. This is the only known practical drawback of photogrammetry. This can easily be fixed by messing up the surface you’re photographing, giving it points to hold on to when aligning. The drawback of laser scanning is that devices (Handheld IR scanners, Lidar scanners) are ridiculously expensive.
Today photogrammetry has many applications. Aerial Surveying and Mapping, Engineering, Manufacturing, Cultural and Heritage preservation, Police Investigations, Geology, Archaeology, Architecture, you name it. Other than these fields, the most common field is the gaming industry. With photogrammetry, more complex models can be created in hours, which may take days or weeks to complete with modeling. And the outcome is absolutely astonishing. Ultra-realistic models that are used in most video games today are there because of this technology. Battlefield 1, The Vanishing of Ethan Carter, Star Wars Battlefront, PlayerUnknown’s Battlegrounds and Red Dead Redemption 2 are a few of many games that use photogrammetry.
Surveying and Mapping with drones is the next industry that uses photogrammetry heavily. Creating maps for larger fields with drones and photogrammetry is becoming a more common way of mapping day by day. Images that are taken with a drone are then rectified with defined control points to get a more precise map with some fitting, trimming and some tweaking.
The first evidence of photogrammetry is also related to surveying and mapping a building in 1502 by none other than Leonardo Da Vinci. He developed the concept of perspective and projective geometry around 1480 and through that he developed the map of the town of Imola in Italy for a conqueror named Cesare Borgia. Borgia didn’t have a geological idea about the town he conquered and by employing Da Vinci to make the map, he used his artistic skills for the cutting-edge, groundbreaking creation of surveying history.
Since Da Vinci published the concept of perspective and projective geometry, many mathematicians and scientists have developed and helped photogrammetry to evolve over the years. Even as we speak, this technology is getting better, adapting to serve more fields than it did before.