Using Drones to Survey Quarries
Aidan O’Connor, the managing director of ASM Ireland, is one of the country’s most knowledgeable commercial drone operators, with particularly extensive experience in the field of quarry surveying. Waypoint caught up with Aidan to blast through the benefits of using drones over terrestrial instruments and to drill down into the different ways drone data can benefit quarry operators.
Hi Aidan, and thanks for your time today. Can you maybe start us off with an overview of ASM Ireland, particularly your work with quarry clients?
Sure. At ASM Ireland we specialise in aerial surveying with UAVs. In fact, we were the first Irish company to do so. We fly the senseFly eBee, and from its aerial images we produce georectified maps from which we can accurately measure distances, areas and volumes.
We’ve worked on all manner of large projects across the country, from road design and construction to landfills, coastal erosion protection projects, wind farms and golf courses to name just a few. We do however specialise in quarry mapping. Our civil engineering background gives us a big advantage when it comes to understanding exactly what a client needs from a survey and we can then add significant value to the raw survey product.
I would say we’re probably one of Ireland’s most experienced aerial quarry surveyors operating today. We’ve completed hundreds of flights with the eBee, from projects that are a few acres in size to large operations of 100 hectares and above, with the majority being quarries.
What are the benefits to quarry owners of employing a drone surveyor compared to a supplier who uses traditional instruments?
There are two main benefits. The first is pure efficiency.
If we take one independently-operated limestone quarry that we worked on in the South West of Ireland as an example, our survey was required for a planning application that the owner was undertaking. With the eBee, a full aerial survey of their 88-hectare site took us four to five hours. Around half of that time was spent placing our control points, which can take two to three hours, depending on the terrain.
For them to get even close to the same level of detail as the drone, using terrestrial methods, it would probably take that single surveyor upwards of two to three weeks
Traditionally, a surveyor using terrestrial equipment would likely use a combination of GPS (GNSS)—for quicker ground coverage of surfaces like floors and fields—and a reflector-less total station to get working faces, which are dangerous and inaccessible to terrestrial GNSS, all the while working around heavy machinery. For them to even get close to the same level of detail as the drone, it would take that single surveyor upwards of two to three weeks, although obviously, a small team would do it much quicker.
Explore a point cloud fly-through from Aidan’s example quarry survey:
How does the number of points compare?
The drone’s point cloud, for this particular site, contains 44 million points. At most, with terrestrial surveying, you’re looking at a few thousand. It could even be a few hundred, depending on the topography, and even with this figure you’ll be relying on a huge amount of interpolation between points to calculate large areas.
You mentioned two key drone benefits. What’s the second?
It’s safety. In my experience, surveyors often take precarious risks to get to edges and they have to work close to machines that sometimes weigh more than a hundred tons. With a drone you don’t need to get out to those edges, you can launch and land at the perimeter of the site or even outside it, and with the speed of a drone survey you limit the time the surveyor spends on site.
We typically have a virtual copy of the quarry ready less than 24 hours after being on site
How much time did you spend processing the drone’s images in order to create the 44-million-point point cloud you mentioned?
For this job, in fact, for most of our quarry surveys, the processing takes a few hours. We generally process our data overnight so that projects are ready when we return to the office the next day. We typically have a virtual copy of the quarry ready less than 24 hours after being on site.
If we stick with this same quarry example, were your deliverables simply handed to the client and you moved on to your next project, or did some joint analysis also take place?
Once we had processed the data, we sat down with them on site for half a day. We discussed and virtually placed, in 3D, their new plant items in various parts of the site in order to check issues such as sight lines, excavation volumes, interruptions to existing workflows etc.
I believe they will also now carry out some noise modelling, using our survey to predict noise levels at the boundaries of the site.
In addition to the eBee outputs, we also generated a full traditional contour map for their planning process whereby we digitised everything on site into AutoCAD format.
What kind of detail did your final orthomosaic of their site show?
Incredible detail. The final orthomosaic’s GSD, or ground sampling distance, was three centimetres per pixel. To put this in context, it was over 30 times higher resolution than the next available option. The ortho, or photo map, on its own, is an incredibly valuable asset when it comes to planning operations, as it means the smallest detail can be taken into account.
And in terms of the absolute X, Y, Z accuracy of the data you supplied?
We generally quote that accuracy will be in the region of 50 to 100 millimetres, or two to three times the GSD of three centimetres, in this case, six to nine centimetres, which would be standard for the industry and processing software. Our checkpoints however usually confirm an accuracy in the region of sub-five centimetres.
“Wow” is generally their first reaction to the level of detail, but it’s when you explain what they can do with the data that they get most excited
You’ve carried out numerous aerial quarry surveys, for numerous clients, over the past few years. What is the typical feedback you receive from a new quarry client when they see the drone’s results for the first time?
“Wow” is generally their first reaction to the level of detail achieved. But it’s when you explain what they can do with the data that they get most excited. Using our engineering background, we squeeze the most out of every possible dataset. We always say that the flight and processing is just the beginning.
We often hear anecdotes from clients who wish they’d had the drone’s data, for a certain problem, going back years. They lament how much time it would have saved. We get that quite a lot actually. The advantage, when problem-solving, of having a virtual copy of your site to explore, can’t be underestimated.
We often hear anecdotes from clients who wish they’d had the drone’s data, for a certain problem, going back years
That’s the beauty of a UAV survey—all manner of detail is collected. It may not necessarily be required at the time but we’ll often get requests from clients months or even years later asking if we captured a particular detail, and almost always, if it’s visible from the sky, we’ve collected it.
Lastly, could you talk us through the ways in which your drone’s data is used? How do your clients employ the deliverables that ASM Ireland supplies to guide and optimise their activities?
Often we go into a quarry to solve one particular problem, but our maps, particularly our digital elevation models, end up being used for a huge range of purposes. These include calculating stockpiles or reserve, and during planning exercises, we can create cross sections and we can digitise the orthophoto—meaning all the detail in the orthomosaic can be digitised into a CAD format.
We also use the drone data for environmental impact planning and reporting, managing property and boundary mapping, health and safety planning, and for blast planning, to name just a few.
With the drone and the Pix4D processing software, we effectively get the whole site, in 3D, on our desktops. You get an enormous amount of detail, so from different aspects, you can see all the stockpiles, all the buildings, everything is mapped.