The general trend in all industries is automation, the aerial photogrammetry industry is no different. The advent of digital cameras and poweful computing platforms has automated the image processing workflows from the film camera days. The advent of electric powered aircraft and affordable, small autopilots has made the business of flying and capturing imagery automated as well. The industry has started drawing on all the UAV experience garnered in the defence research and hobbyist arena into commercial products.
There are several components to a UAV based photogrammtery platform. The UAV airframe is only a very small part of the equation, a lot of other pieces need to fall in place to allow a successful aerial photogrammetry project to take place commercially.
Airframe construction and durability:
Most hobby level aircraft are only constructed out of foam, higher speed airframes feature fiberglass, composite or aluminium alloy constructions. Repeated use of the airframe would require a higher quality construction and failsafe methods of landing and recovery, such as parachute recovery. On the other hand the airframe can be treated as a disposable part of the project and used with the aim to do discard it at the end, for reasons discussed later this approach will not be feasible due to certification reasons.
Autopilot and Ground Control Station:
Removing the pilot from the airframe necessitates the use of very advanced autopilots and ground control systems with reliable radio links between the ground station and the airframe. Software for the ground station is typically custom designed for the given autopilot and is an essential part in both training in simulations and actual field survey scenarios. Apart from electronic tethering the aircraft needs to be kept in visual range while in operation.
Camera System and Flight Planning:
Weight of the camera is the deciding factor in choosing which one to use. Cheaper systems go for Canon Powershot models since they can be made to automatically trigger using CHDK firmware. More advanced systems use micro 4/3 cameras to achieve DSLR like image quality and resolution with more compact cameras. The triggering is attached to the autopilot and flight planning stage is critical in getting frame density with proper overlap and ground resolution. The low operating altitude of these unmanned systems can result in large variations in ground sampling distance due to terrain changes in the different parts of the project, flight lines as well as altitude needs to be configured to account for this.
Air space regulations and Certification:
The largest hurdle to an operational UAV acquisition system is operating it safely within the airspace requirements put in place by CASA or other regulatory body. Commercial usage removes all the liberties hobbyists have in operating model aircraft and exposes the operators to liabilities
due to failures. Extensive safety guidelines need to be followed and use is limited to non-urban environments where the airspace is uncontrolled. Training of the operators has to be carried out to exacting standards in order to meet approval requirements.
Ground control and in airborne GPS:
As in all high detail aerial photography projects, the area under survey needs to have control and check points. Size and weight constraints on the UAV limits the quality of the IMU and GPS units available for capturing the camera position and exterior orientation. The limitations in this aspect are compensated by modern image processing techniques to improve relative positioning.
Dense matching and Orthophotography/Point-cloud generation:
The UAV generated aerial imagery is typically co-registered and triangulated using dense matching techniques. The flexibility of the flight paths the UAV can follow and the low altitude at which photography takes place makes it possible to plan for oblique as well as vertical photography of the areas of interest. This multi-view geometry can then be exploited to produce strong triangulation results, augmenting the relatively week on-board positioning information. The end products are point-clouds in true 3D in addition to traditional ortho-photography and elevation models in 2.5D.
In field operations and travel to site:
The short range and endurance of smaller UAV platforms requires positioning via ground transport to the survey area. In the remote mining areas trained operators are needed to regularly fly the aircraft for monitoring purposes.