Photography for Engineers
By John Kendall
The buzzword around diving and archaeological circles is photogrammetry, or structure from motion.
But what does that mean? Put simply, photogrammetry is the science of making measurements from photographs.
Cool, but still, what does it mean?! You can create awesome 3D models that help you contribute comprehensively to the meticulous and proper documentation of the sea floor and more in the name of exploration and preservation. By taking thousands of high resolution photographs and using some pretty clever techniques and software you can make a virtual 3D model that can be used as an effective tool to share the great unexplored with the land dwellers.
The basic principles were first described by Leonardo Da Vinci in 1480 as he developed the concepts of perspective and projective geometry. Through the 19th century as cameras became more available, enterprising photographers started using their photographs to create maps. Early attempts often involved climbing towers to cover more area with a better angle. As inventors developed early airplanes and balloons, photographers were enthusiastic passengers, taking images and using these images to create more maps.
As the world marched into 20th century, and the world went to war, the pace of aerial photography and photogrammetry development accelerated, as both sides raced to find faster and easier bombing each other, mapping battle lines, and assessing damage.
In the 1950s and 1960s scientists and mathematicians developed formulas that could be used to automate photogrammetry. However, it wasn’t until the later parts of the 20th century that these formulas could be used, due to the computing power required. Due to the massive number of calculations required to align photographs for photogrammetry, early computational efforts were performed mostly by governments and universities. More recently, personal computing has caught up, allowing amateurs and smaller businesses to automate photogrammetry. In particular, the rise of small personal unmanned aircraft (drones) has given the software industries the impetus to develop user friendly tools for creating models from aerial photography – tools that are adaptable enough to be used for other photogrammetry projects as well.
Shifting the focus from aerial photography to underwater photography did not take that long. While a number of people had started to use photogrammetry for underwater modelling, the true value of the technique didn’t become clear to the public until the Ocean Discovery team found the wreck of the Mars in Sweden in 2011. What the Lundgren brothers and the Ocean Discovery team achieved with their early documentation of the wreck was truly astonishing. The 3D model of the historic warship Mars captivated the public, and gave angave an unprecedented view of a historically fascinating wreck.
Modern photogrammetry involves taking two dimensional photographs and building 3D models out of them. This process requires taking hundreds to thousands of images and then using software to process them into a “point cloud.” A point cloud is a collection of points in a 3D virtual space, where every point represents an edge or corner in the final model. The point cloud is created by the software identifying distinctive marks and edges that occur in multiple photos. By using complex math to examine spacing and angle change between the images, the computer is able to calculate the original camera positions in 3D space and produce a low quality 3D model of the object that was captured.
Point Cloud Image.
With the camera positions calculated, the computer can add extra detail in to the point cloud by creating a second point cloud with many more points, which is known as a “dense cloud.” Creating this dense cloud is the most computationally intensive phase of building the model, and can take many hours (even on a relatively small model).
For larger image sets and more complex models, this step can take days, weeks, or even months. The incredible Mars model created by Ingemar Lundgren and Dirty Dozen crew member Richard Lundgren took in excess of 18 months to process, even with high end computer equipment.
This was a significant discovery in maritime history and such techniques had never before been used to create a 3D model accurate to 2mm, underwater. Check out the video of the Mars model here.
A 3D model of Mars Makalös made using photogrammetry by Ingemar Lundgren, Ocean Discovery ©
After the dense cloud is created, it is used use this to create a solid surface. We call the solid model a “mesh.” This is similar to a child playing “connect the dots” – the software builds the dense cloud model (made of thousands or millions of dots) into a solid object.
Mesh Image.
The final step in creating the 3D model is to use the original photographs to paint the surface of the mesh, a process called “texturing.” Texturing allows us to add details to the model that were too small to be shown as structure in the mesh. This process is not quick, and it requires a reasonable amount of computing power, but luckily for us the computer gaming industry has already developed computer components (graphics cards) that are optimised for this process. We can take advantage of their hard work and the commercial availability of gaming graphics cards to make this step go quickly. Once texturing is complete, an incredibly detailed 3D model is reviled, complete with the colour present on the original.
Textured Mesh Image.
We wanted to tell you about a very exciting trip for all the photographers out there with our photogrammetry wizard - GUE Instructor Trainer, Fellow of The Explorers Club and archaeological diver John Kendall who will be joining our trip to Truk Lagoon in November 2021.
If this sounds exciting to you join our team as we explore the wrecks underwater and then go deep during the evenings with a series of workshops and masterclasses where John will guide us deeper into the 3D modelling of larger wrecks, how to integrate detail into large scale models and work on perfecting our skills.
And yes, it is as always when booking with us: enjoy small deposits, flexible payment terms and friendly booking conditions because we want you to get down, dirty and clicking away at some of the most infamous wrecks on the planet.
Send us an inquiry now here for to find out more before the spots sell out.