For many people drones are used for military air strikes or reconnaissance missions. However, today Autodesk University's Mike Gemmell explained how these small helicopters are used within the architecture and engineering industries as an inexpensive and faster alternative to traditional surveying techniques. Images captured from drones carrying laser scanners or digital cameras can utilize software such as Autodesk's Recap to create 3D models of large structures and spaces. The process is called reality capturing and can achieve highly accurate proportions that aid architectural projects. Gemmell's AU discussion focused on using cameras (aka. photogrammetry) to create 3D models.photogrammetry. The AU researcher has been studying and experimenting with drones and cameras several years looking for the most cost effective combination. In addition to equipment compatibility, Gemmell also looked at various flying/tracking techniques that could yield the best coverage for the Recap software. You can watch the entire AU session at Autodesk University's website. Below is a synopsis of the information about drones and cameras for anyone looking for effective equipment and techniques to implement reality capture into their own 3D projects. Learning to Fly Drones Gemmell stressed the need to start with something simple and inexpensive. "As you're learning [to fly], you will be crashing a lot" he stated, "So the smaller drones are best because you can fly them inside or outside." He also suggested that learning to fly drones didn't need to be a formal affair. In fact, he said he gained most of his skills by playing war games with his son who attempted to down his drone with a NERF gun. "I was winning until Santa Clause bought him an automatic NERF Gun," Gemmell recalls. Custom building drones is also an option, and this was something he also experiment with, even offering his own custom-made 3D drone model to anyone to us.

Choosing a Drone Type

There are negatives and positives to the type of drone you choose. Again, Gemmell stressed starting out small and cheap. A tricopter (three-armed) is inexpensive, light weight, and easy to fix if you crash it. However, it's not as powerful as other multi-armed drones like the ocotocopter, which provides good lift and a redundant power supply system. However, it doesn't do well in windy conditions and has a short flight time. What's essential to getting good reality capture shot data is control and steadiness. "Drone flying for Recap is much different than drone flying for recreation," he Gemmell states, "Drone flying for Recap is basically hovering, and fighting the wind, and putting this thing in the right place in space to take an effective picture that will make a 3D model."

Cameras for Drones

Gemmell experimented with several cameras including the GoPro Hero 3 and the Sony A7R. Obviously weight is an issue when equipping a drone with a camera. The lighter the better. So the GoPro would seem to be a natural choice; however, Gemmell also concluded that the GoPro's smaller sensor just didn't' provide the resolution needed when zooming in on architectural details. One of the things you have to also consider with a camera are settings like ISO and shutter speed. Many settings have to be adjusted prior to launch of the drone since you obviously can't change them from the group. Lens choice for you camera is also a crucial decision. Overall, Gemmell said that he found the following characteristics important for a drone camera lens:

• Prime (fixed focal length) better than zoom (you can "zoom in" by moving the drone closer)
• Wide angle usually better than longer focal distances
• Manual focus to infinity better than auto focus

Sequencing your Photos

Other than having a clear photograph, one of the other key elements of photogrammetry is sequencing your photos correctly. With potentially thousands of photos of a building, city block, etc. keeping track of which photos go first in the sequence is crucial to an accurate 3D render. This is because reality capture software like Recap identify re-elements within an image and base their measurements on these constants. Having elements shifting back and forth forces the programs to "guess" as to what an object should look like. If you photos are out of sequence, this can create substandard results.  Luckily, Recap makes sequences a pretty easy task because it's designed for these types of inputs and changes. Organization is really the key. Gemmell's presentation is full of good information for for both commercial and recreational projects and you can watch the entire demonstration at AU's website. You can also download a PDF of the entire session's slide show.