The Future of Aerial Photogrammetry

Rapid advances in technology are changing the way we map from the air, but the 100-year-old technology of mapping by crewed airplanes will continue to fly into the future

For thousands of years cartographers made maps using tools that mostly measured angles and distances, allowing for positioning of fixed objects over unknown topography. The earliest map in existence is the Babylonian Map of The World, a clay tablet also known as the Imago Mundi and going back an estimated 700 years BC.  

Since then, cartographers have helped humanity venture into new worlds, literally, by providing semi-accurate descriptions of coast lines and allowing intrepid navigators like Christopher Columbus and Ferdinand Magellan to reach farther and farther into the unknown. 

Cameraman and navigator during crewed mission.

Tools became more sophisticated and eventually at the end of the 19th century, with the arrival of photography, a new science was born when two images were used to create a three-dimensional view of an object, which became known initially as “photometrographie” and eventually became photogrammetry. 

Then, as usually happens with wars, the technology was used to create a strategic advantage when a camera was mounted on an airplane and a sequence of stereographic pairs was used to compile highly accurate maps of battle fields. That was the beginning of the next great revolution in mapping, aerial photogrammetry, and when we put things in perspective that was only 110 years ago. When compared to the timeline since the Babylon map, it is just a fraction of the history of our profession and the period where the most progress has been made in terms of technology, processes, and procedures. 

After World War II, with the introduction of the jet engine, better cameras, and vacuum pumps, aerial photogrammetry took the next leap when aircraft could fly higher and better optics and self-stabilized mounts allowed for great resolution images and better maps of larger areas. 

Then, in 2013, one of the larger suppliers of geospatial hardware and software, Trimble Navigation, launched the UX5, a non-piloted aircraft that promised to revolutionize, once again, the art and science of making maps. 

Happy pilots during a crewed mission.

Almost simultaneously Leica followed suit and the race was on to add a new tool to the wide arsenal of land surveyors all over the world who suddenly were able to upgrade their operations to include aviation, a field that until then was reserved for large corporations with deep pockets and large payrolls.  

As with the introduction of any new technology, doom voices are predicting that crewed aerial photogrammetry is bound to disappear and be replaced entirely by uncrewed aircraft roaming the skies autonomously mapping the Earth. 

Well, we have heard similar predictions before and none of them came true, at least in our profession. Aerial photogrammetry did not end ground surveying, GPS did not eliminate the need for transits, and mapping satellites did not end the era of the crewed photogrammetry aircraft. 

Garmin 750 showing flight lines over the Gulf of Mexico.

A simple math exercise will tell us that the complete replacement of crewed photogrammetry, if it comes at all, is still a few decades away. Take, for example, the flying time of most uncrewed aerial platforms today. If you are unlucky enough to be using a multi-copter, get ready to have flying times of 25 minutes or less and to be constantly within visual range of the operator, which greatly reduces the areas to be surveyed to the immediacy of roads or very long walks with heavy backpacks. 

If, on the other hand, you are using an uncrewed fixed-wing aircraft then you are looking at flying times that are double that. Even more, the visual range still applies, therefore the constraints of area per flight do not improve very much. 

To start with, conventional crewed aircraft can fly higher, are permitted over the National Airspace (NAS), can fly longer, and have larger camera format and lenses. All of these factors combine to create a huge gap with smaller aircraft, which cannot exceed altitudes higher than 400 feet, have small cameras, and fly at lower speeds. 

One of the main issues with UAV photogrammetry is that cameras are small format and therefore their footprint on the ground as they take photographs is also proportionately small and the area covered pales in comparison to the larger formats of crewed aircraft. Large format cameras normally installed in crewed aircraft use large 230 mm sensor width, while UAVs can carry medium format (53.4 mm) or small format (23.5) cameras. 

Area covered by a 230 mm photograph installed on a crewed aircraft.

As you can see by the stark difference between coverage using a large format at high altitude and a small format at low altitude is compounded by many factors. 

One issue that both crewed and uncrewed platforms have in common is the sun angle or in other words, the window of opportunity for photogrammetry photos to have the right shadow length in order to be usable. 

Area covered by a medium format (53.4 mm) photograph installed on a drone.

In my experience over 40 years of flying at every possible altitude and aircraft type is that nothing before 9 a.m. or after 3:30 p.m. should be used for cartography. There might be exceptions based on terrain and seasons of the year, but in general photogrammetrists develop this sixth sense that tells them if an image will be rejected by the office or not. That is why rules of thumb are important for people who are starting in the business. 

So, if we have only six hours of effective flying in a perfect weather day, would photogrammetrists choose to use a platform that can cover a few acres in that perfect day or something that can cover thousands of acres on the same period of time? 

The answer, unfortunately, is not black or white, it is a kind of grey, as usual. The same way that new technologies rarely replace completely established processes and procedures, photogrammetry drones are here to offer an alternative to photogrammetrists by adding to the menu of possibilities when deciding on the right platform for the job. 

Babylon Imago Mundi – Circa 700 BC – Image courtesy of the British Museum.

In an article last year in this Heights supplement to xyHt about mapping the surface of the ocean over the Gulf of Mexico, I described a mission in which we needed to photograph the entire oil platform infrastructure of the Mexican oil company PEMEX. It was a mission that extended 50 miles offshore, flying at 10,000 feet and 240 knots. In other words, not a mission for a drone, not even close. 

On the other hand, if we have a mission that requires mapping 400 acres of agricultural land for mapping at 1:5000 scale with contour lines every 50 cms, this is the perfect job for a fixed-wing drone with a small format camera. 

We live in an era when there are tools for every job, from smartphone-based GIS data collectors, to million-dollar full-format aerial cameras. Land surveyors, photogrammetrists, cartographers, geographers, and many others in our profession and our industry have more tools than ever and we can safely say that after 2,723 years mapping the same ol’ Earth, we are still having fun and enjoying the great outdoors as we help humanity understand its surroundings in order to progress and improve our way of life. Drones are just another tool.

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