UAV Use for Open Cast Mines and Quarries

A 1.625Mb PDF of this article as it appeared in the magazine complete with images is available by clicking HERE

Drone is a word that drives fear into the hearts of numerous citizens. It is technology that has been privileged exclusively to the super powers of our world and the military. Fortunately, times have changed and this secretive knowledge has trickled down to the ordinary citizen in the street. Avenues have opened up, allowing opportunities for solutions which have previously not been available.

The field of available applications are growing at an exponential rate, making it nearly impossible to concentrate to any specific field of application. What we would like to discuss is the application of Drones in the Open Cast Mining Industry, a field that is rather restricted in information due to the limited amount of users in Africa.

Surveyors in Africa have traditionally been very conservative and still are, accepting new technologies with a bit of scepticism.

As surveyors, we have always strived to find and develop new technologies, which we can apply in our work, enabling us to deliver an enhanced service to our clients. We have been involved in our own research and development for the last couple of years and together with other available technologies have put together systems that work for the Open Cast Mining Industry.

In designing these systems, the following goals had to be achieved:
Safety: safety is of paramount importance to us.
Accuracy: using conventional surveying methods with either a Total Station or GPS, our system needed to be more accurate than these methods. Using a Total Station or GPS, the Surveyor is restricted to the amount of detail that can be recorded, due to the time constrained. We do not have these issues with our systems.
Productivity: we needed a system that gave quicker end results than conventional methods, realizing that time is money with our Clients.
Workflow: we realized that we needed a system that was partially or fully automated. This included from planning the mission, flying it and eventually processing the information.

In our research, we have found that Multirotors are more suited to Open Cast Mining Surveys than Fixed Wing Planes. Here the Phantom 3 Professional or Phantom 4 is an ideal platform for these types of Surveys and then there is our own "Sputnik", which is slightly larger, can withstand stronger winds and has a longer flying time.

An aerial survey is not a matter of simply flying a site, taking pictures and dropping them into a software program. Articulated in its simplest form, that is exactly what we do, but theory and reality are very different.

Let us follow a typical Quarry Survey:
Arrive on site and familiarize yourself with the Terrain.Note the weather conditions.
Identify any safety issues and take the necessary actions.
Place markers evenly spaced over the site to be surveyed and fix the positions of the markers using a survey grade GPS.
Plan your mission, ensuring that you fly at an optimal height for the required resolution and have at least an 80% overlap on your photos in both directions.
Once the mission has been flown, download the Images to your Processing Software. Here we have found that Photoscan and Pix4D produce the best results. Then we have our own in-house developed program called "TopoSurf".

Unlike other aerial providers, our solutions are not constrained by flight schedules, fuel consumption, or airstrip availability. Our UAV solutions are flexible, reliable, and safe. Using state of the art winged and multirotor technologies, we can arrive on-site and be airborne within 10 minutes or less. We launch and land on-site. We are as flexible as the project demands.

Flying the UAV
After proper pre-flight inspections, the UAV is launched and once it has reached its predetermined height, the UAV immediately starts with the programmed mission collecting georeferenced aerial images, which are stored onboard an SD card. In addition, live telemetry data is streamed down to the ground station, containing vital information such as heading, speed, air and ground speed, battery status, mission progress, etc. thereby allowing us to monitor the UAV and the mission progress. Live video streaming is also send down from the onboard camera to the ground station.

Hundreds or even thousands of photographs are taken of which only a percentage will actually be used to render the final products. This is intentional, as it allows us to be selective, choosing the very best outputs with which to work. Below is a sample of one such composite.

The Point Cloud
Next comes the point cloud. Unlike the mosaic shown before, the point cloud is generated using many more photographs, and its creation is where GPS ground control is entered into the process. We are in the process of looking at alternative technology where the necessity of ground control points will be obsolete. The point cloud forms the mathematical base for the subsequent analysis that will be performed.

All of the points gathered are used to create a TIN model. A TIN (triangulated irregular network) is a digital mathematical data model used for the representation of a surface. From the TIN, we are now able to render contours. Our process begins with tightly controlled captured data at a resolution of 20mm, resulting in significantly reduced interpolation requirements. Subsequent generations of deliverables are based on that initial data capture, so our ability to deliver contours at tighter intervals is a default. This is sometimes an educational issue as our clients are accustomed to tighter controls representing additional cost. Our default contour spacing is 250mm; there is no cost variance whether the Clients wants 500mm or 100mm contour spacing.

From the final digital elevation model (DEM), we are now in a position to calculate StockpilePit volumes.

Aerialpix (Pty) Ltd has proven that UAV technologies can capture accurate data for highly refined volumetric analysis. We have been told, repeatedly, that the level of detail we are able to produce exceeds anything our clients have ever received. We are pleased to know that an idea that came to us as a loosely framed thought, a simple "why not," has not only been proven, but has surpassed all expectations.

Jessica has been involved in surveying for the past 12 years and her passion for technology, related to the surveying industry, has turned her attention to UAV’s. She has been involved with UAV’s for the past 3 years and together with Michael they form a formidable team, contributing and guiding others towards the success of the Company.
Michael is a qualified Civil Engineer, but his passion for technology has driven him towards the Surveying Industry. From an early age in his career he has searched ways to automate the workflow in the Surveying Field and hence his interest in UAVs.

A 1.625Mb PDF of this article as it appeared in the magazine complete with images is available by clicking HERE