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Drones as a measured survey tool

Cory Hope | 12 Apr 2016 | Comments

Cory Hope looks at how ‘drones’, or Unmanned Aerial Systems, are increasingly being used for surveying, and how doing so helps to improve data accuracy, lower costs and reduce health and safety risks.

There’s rarely a day that goes by that drones aren’t in the media, typically in either a hobbyist or military context. When it comes to their application in the commercial sector, I prefer the term Unmanned Aerial Systems (UAS). This definition considers the whole system including the pilot, the flight planning and control software, navigation hardware, sensors and, of course, the aerial vehicle itself.

Although UAS have wide ranging commercial applications in many sectors, I’d like to look at their use for measured survey. By this I mean any survey where the subject’s position and/or dimensions are accurately measured in 2D or 3D resulting in an accurate digital representation. These kind of results can be achieved by using a UAS fitted with off-the-shelf digital cameras, then processing the imagery with specialist software to create a variety of products and services. While it’s also possible to attach lightweight laser scanning devices to UAS, this is typically limited to larger rotor-based vehicles due to the weight requirements and is therefore less common.

To ensure sufficient imagery is collected in the right configuration, the UAS is used to take overlapping or ‘stereo imagery’. This stereo imagery is then used to produce the key initial output which is a point cloud. A point cloud is a set of data points within a three dimensional space. With the right flight planning it is also possible to produce stereo models enabling the imagery to be visualised using 3D monitors and 3D glasses similar to the kind of you could buy for your home.

Standard UAS survey products are mostly limited to point cloud, digital surface model and orthophoto (photo map) products which are generated automatically by proprietary software. Sadly these products often include inherent errors which limit the accuracy and usefulness of the data. However, with additional processing, using specialist software and survey knowledge, these errors can be removed, improving the quality, usefulness and value of the resultant data sets. By taking this extra step, data can be used to properly inform engineering design, for Building Information Modelling (BIM), Geographic Information System (GIS) analysis, for 3D visualisation or to create virtual or augmented reality.

Undertaking discrete UAS measured surveys is becoming commonplace on today’s construction sites, in quarries, mines and other areas where this remote technique can replace the need for staff on the ground, reducing health and safety risks and lowering costs. However, this technology is only starting to be exploited to its full potential. This is largely due to the industry’s reliance on automated software processes by new entrants to the market and a lack of application of robust survey techniques and sound photogrammetric knowledge.

The ability to define complex 3D flight paths for UAS measured survey means that complex structures and buildings of all shapes and sizes can be surveyed to a consistent accuracy in a fraction of the time to undertake a ground-based laser scan survey of the same area. In addition, a UAS with a gimbal attached can take images at a variety of angles from almost any position minimising or eliminating the restricted sight lines typically found in ground-based laser scanning surveys. High detail photo realistic 3D models can be relatively easily produced and provided as ‘as built’ 3D models for BIM working.

In the future, the ability for multiple UAS devices to act in a ‘swarm’ which communicate with and avoid each other and operate semi-autonomously will present opportunities for frequent or real-time monitoring of construction sites, highways, railways, mining or any other element of the built environment. The imagery collected could then be automatically processed and fed into the project GIS or BIM implementation, in turn generating progress reporting and comparison analytics.

Unmanned Aerial Systems have added an extremely valuable tool to the surveyors’ already bulging technology toolbox and provide unique capability which will result in their increased use for measured surveys. However, the speed at which this technology will be more widely adopted is limited by strict Civil Aviation Authority regulations on how and where UAS can be flown commercially and the way in which data is collected, processed and interpreted. I believe that if these issues can be addressed then the use of UAS for measured survey will become standard practice for many applications.