By Frank Willis
During the past 50 years, surveying and engineering measurement technology has made five quantum leaps: the electronic distance meter, total station, GPS, robotic total station and laser scanner. Unmanned aircraft systems (UASs) or drones (also known as unmanned aerial vehicles or UAVs) will be the sixth quantum leap in technology. Although drones have been around for awhile, the technology has not yet been widely used in the surveying and remote sensing professions. But it soon will be, thanks to the advent of practical, lightweight lithium polymer batteries, low-cost drone technology, lightweight digital cameras and advances in close-range oblique aerial photography—all of which make the future of drones in land surveying exciting.
There are two basic types of drones—fixed-wing units with a brushless electric motor and a rotor type that has between three and eight or more brushless electric motors (commonly referred to as multirotors). The rotor units enable drones to hover at a precise altitude and position and operate in confined airspace. The technology for both systems relies on the featherweight lithium polymer battery that stores an incredible amount of power and the brushless motors that have a large variable speed range with good power at all speeds, lightweight airframes and a simple, hobby-type airplane radio controller. GPS and altimeters enhance their capabilities. Small, on-board video cameras with micro-video transmitters enable pilots on the ground wearing digital video headsets to “fly” as though they were sitting in the pilot’s seat.
A basic, eight-engine, multirotor drone consists of a lightweight airframe that resembles a spider with the motors at the end of each leg. The “body” of the spider contains a lithium-polymer battery that sends power to small devices called electronic speed controllers (ESCs). Each motor has an ESC. The unit has a control system that regulates the speed each ESC tells each motor to rotate. The control system is operated by a chipset equipped with an electronic gyroscope that is about the size of a pencil eraser and by a similarly small accelerometer chipset.
The operation is logical. For example, if the drone is hovering and one side needs power to level the craft, then the sensors detect the tilt and the control system automatically adds power to the engines on the low side. The “pilot” on the ground can override the ESCs manually with a radio to control flight. Half the motors spin clockwise, and the others spin counterclockwise. Yaw is accomplished by changing the speeds of opposing motors to create a very small torsion perpendicular to the vertical axis without creating differential lift.
The control accuracy of a multirotor drone is extremely precise. Drones can fly at incredible speeds horizontally or vertically, reach 400 feet in a few seconds, hover and stop on a dime. I have demonstrated my eight-engine, 18-pound drone in conference rooms.
Until recently, most of the affordable drones consisted of purchased parts “with some assembly required.” I purchased my first drone from Mikrokopter, a German company. The instructions were in German, so I had to use Google Translate to interpret them. The package was a box of electronic parts that required dozens of soldered connections, and it took me more than a month to assemble it. Huge demand for drones has stimulated competition, and now a multitude of companies are manufacturing drones. The kits are much easier to assemble than they were six months ago. Two other substantial players in the market are DJI and Hoverfly Technologies.
Drones will be a perfect platform for aerial photography and remote sensing. The built-in accelerometer and gyroscope that control flight can also be used to simultaneously control motorized camera mounts to keep the cameras level and correct for undesired tip and tilt caused by wind or a shaky pilot. Mikrokopter, DJI and Hoverfly drone controllers allow the uploading of GPS or Google Earth data to compute flight path coordinates and automatic route flights. The planning software also enables the planner to enter specific routes, speeds, altitudes and hover times over each point.
Recent technology even enables the drone to land automatically. Failsafe technology constantly checks for the quality of signals from the ground radio control, and if the signal is lost, the drone goes into hover mode; after a few seconds, the drone returns like a homing pigeon to wherever it took off and lands automatically. The controller can also press a “come home” button, and the drone will return to the takeoff coordinates at a preset altitude and land automatically.
The camera angle can be changed in real time by the pilot to provide settings from horizontal to vertical. The gyro stabilizer controls the camera to keep it oriented in a constant direction and is excellent for semi-orthometric aerial photography. An inexpensive camera intervalometer can trigger the camera to take still photographs at time intervals of one second or longer, so that the pilot is not overwhelmed by having too many controls (a potential problem for inexperienced pilots). The systems also provide video using digital cameras such as the CanonT4i, GoPro or a cell phone. The GoPro can be connected to an onboard video transmitter to send VGA video signals directly to a small ground receiver connected to a video headset. Camerasharp is a great iPhone camera intervalometer, and photos taken from a drone are surprisingly sharp.
Photographic field of view is important in aerial photography, since it is proportionate to flying height and the size of the camera sensor. Small drones do not provide nearly as large a field of view as standard professional orthophotography. However, advances in photogrammetric software, CAD software and wide-angle lenses help to offset the disparity. Field of view can be calculated using a common survey calculation of similar triangles. The flying height and ground coverage are directly proportional to sensor size and focal length. I use a Canon T3i with a Canon 10 millimeter to 18 millimeter lens, which, when zoomed to 10 millimeters, provides a field view approximately the same width as the flying height. The smaller field of view of small drone photography requires a higher density of ground control than for conventional aerial photography. Small drones are best suited for smaller jobs, offer the convenience of quick turnaround and lower cost, and are generally not practical for large projects covering a wide area.
Many new software packages are available, led by Leica, Iwitness, DroneMapper, Photomodeler and others. Drone photographs processed using photogrammetry software can produce 3D accuracy that is equal to or better than conventional aerial photography. Standard GIS software and AutoCAD can be used to stitch and georeference drone aerial photos. I have obtained surprisingly accurate 2D results using an iPhone and GIS software.
The combination of low cost and easy assimilation of multiple technologies provides significant opportunities for development, including by surveyors and consulting engineers. An excellent GPS-controlled drone with a camera can be developed for less than $6,000. A quick scan of YouTube videos reveals stunning drone technologies, such as groups of drones flying in formation. Possibilities include real-time 3D imaging and an almost unlimited list of others.
However, drones must first overcome the problems associated with safety, privacy and homeland security. Drones penetrate federal airspace, which starts at ground level. According to the Federal Aviation Administration’s (FAA) interpretation, no rules have been developed for drones, so their use is generally illegal unless it falls under the recreational use exemption. The FAA is developing new regulations to license drones, but finalization will be time-consuming.
Regulatory restrictions for safety, although necessary, are the biggest threat to the development of drone technology. Most low-cost drones are not nearly as reliable as manned aircraft and have a much higher crash rate. Videos of drones flying over populated areas are widespread. A small bolt or camera falling from a drone at 200 feet can reach a speed of 70 miles per hour. Overcoming these challenges will require a concerted effort by everyone who has an interest in moving this technology forward.
Once UASs are cleared for takeoff, surveyors and engineers will have the ability to deploy low-cost drones that will fly over a site and collect photography or other remote-sensing data that will improve our ability to measure the surface of the Earth. Keep your eyes on the skies; this remarkable new technology has the potential to transform our profession.