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What value does drone data provide compared to other survey methods?
Mapping and surveying has experienced its biggest evolution in the past few decades from the increased integration of technology, especially unmanned aerial vehicles (UAVs), or drones. However, there are still questions around the accuracy obtained by drone-based land surveys compared to traditional ground surveys conducted by qualified and chartered personals.
Are satellites better than aerial surveys? Are drone maps more accurate than the ground-based manned surveys? These questions have been answered by many experts in their relevant fields. Perhaps, these are the wrong questions to ask. The questions should not be to demand an accuracy comparison between these technologies but evaluate their effectiveness in certain applications.
What is drone data and how does it work?
Drone data is really “aerial data” and can be split into two camps: photogrammetry and LiDAR. Drone data capture works similarly to other aerial capture methods, whereby a sensor is flown over or around an area or object of interest collecting data. The differentiating factor for drones is that they can get far closer to the site than other methods, which in most cases leads to greater levels of accuracy and higher detail.
The most widespread application of drones in construction is through using them to capture a large number of high-resolution photos over an area. In a similar way that the human brain uses information from both eyes to provide depth perception, you can use these multiple vantage points from the images to generate a 3D map. This is called photogrammetry - and has become increasingly popular due to its low cost and weight requirements. Drones often come with added safety and efficiency benefits over the heavier, more expensive systems. You can use these 3D maps to track progress, monitor earthworks, and take measurements without actually having to step foot on site.
3D model captured via drone, hosted on Sensat's Mapp
Is more accuracy always better?
Generally, the closer you get to the ground to acquire data the more accurate the results are going to be. However, the closer to the ground you get, the longer it will take to cover the geographical area of interest. Some projects require a higher level of accuracy than others. Your project goals will determine what level of accuracy you require - for example, a few centimetres for design purposes, or a few millimetres for a live rail project. Someone considering a stockpile survey will need a different level of accuracy than a project with complex topographic contours.
It’s easy to think that a higher degree of accuracy is always going to be better. And in many cases, it will be. Poor accuracy can lead to rework, waste, and increased costs. On the other hand, gathering survey-grade accurate data when it isn’t necessary can create unnecessary complications. The methods that are required to achieve extremely high levels of accuracy can add significant time and increase costs to your project, despite not being necessary or worthwhile for your objectives.
What options are there?
When conducting a topographic survey, you have a few options. The most common of which are the use of satellites, manned aircraft, and ground-based surveys.
Satellites are highly scalable solutions that can provide a very wide coverage of the area of interest relatively quickly. However, they lack spatial and spectral details and are impacted by environmental conditions such as cloud cover. Whilst satellites offer a quick and easy way to capture extremely large scale datasets, it lacks the resolution of other methods.
Aerial surveys conducted by manned aircraft can provide high spectral and spatial resolutions but are not as cost-effective and can also be hindered by cloud cover.
The past decade has seen the emergence of drones that have the ability to provide very high spatial resolution imagery to assist in mapping and surveying. However, these are limited in covering smaller regions compared to satellites and aerial platforms.
Ground-based mapping surveys can be conducted with extremely high accuracy and precision, yet they fail to provide a scalable solution to cover large geographical regions.
All things considered
Drone photogrammetry provides a secure middle-ground. It is scalable, allowing the capture of relatively large terrain without compromising on accuracy, and provides a huge reduction in risk to life by removing the need for boots on the ground in dangerous environments. Instead of requiring surveyors to directly enter dangerous environments, such as a cliff face or live highway, a drone can be used to inspect and survey these environments in a far safer capacity.
Sensat prides itself on being industry leaders in drone data. Through the use of drones, we are able to collect and visualise up-to-date and highly accurate data that is valuable throughout the different design and construction stages.
On the Sensat website, you can find a whole page dedicated to free educational case studies, webinars, reports and tutorials to help you plan, build and manage your projects. Visit www.sensat.co.uk/resources to learn more.