Eltirus

The introduction of cost-effective drones – and the software to process the data from them – has had a revolutionary effect on a range of industries, quarrying chief among them, according to Eltirus founder Steve Franklin.

An effective drone program can be a major boost to pretty much any quarry business. 

The primary benefits are twofold: accurate stock management (reducing the incidence of stock swings, write-offs, and manipulation of figures); and improved collaboration across the business (including provision of up-to-date topography for quarry planning).

We see many companies that have the first of these two benefits in place but are not there on the second, which means they are missing out on at least half of the benefits. We recently passed the five-year mark in terms of drone operations, so now is a good time to provide a wrap-up of where things stand in terms of drone technology, software, and application. 

So what does a good program look like in practice?

OVERVIEW

Just because a company has a drone does not mean it has a drone program or is able to reliably capture survey accurate topography and volumes. 

Some of the key factors at play include:

• having a drone that can do the job
• the ability to fly the drone on a pre-programmed flight plan that will automatically take the photographs at the right time
• having photographs that are sharp and, ideally, all taken at the same (or similar) altitude from the ground
• the fact the location of each photograph needs to be accurately fixed (approximately ±2cm)
• software to “stitch” the photographs together to form a three-dimensional surface (and image)
• a way for stakeholders to use the results in a valuable way; eg to measure stockpile volumes, distances, grade, etc
• risk and quality management.

If it weighs less than 2kg, the associated Civil Aviation Safety Authority (CASA) paperwork and training requirements are light. If it is weighs more than 2kg, however, things are much more complicated.

Our experience over the years has shown us that DJI can be relied upon to build workable, dependable and accurate drones that can be repaired if damaged. Our preference is for the DJI Phantom 4 RTK. This sub-2kg drone has an excellent camera, can be used real-time kinematic (RTK) or post-processed kinematic (PPK), or with ground control points (GCPs) and, importantly, this drone can terrain-follow.

FLIGHT PLANNING

As the phrase would suggest, flight planning needs to occur before you fly. It sets the boundary of the flight, the altitude, and the amount of overlap of the photographs (this is important to ensure you don’t get any gaps in the imagery).

In most cases people tend to only think of flight planning in the horizontal plane – ie flying the drone at a constant altitude over the area to be surveyed. This might work for a stockpile area but will likely not be suitable for an area that has more than, say, a 50m height differential.

It is not uncommon to see operations where the drone is flown at around 75m off the top of the highwall of the quarry, with the floor perhaps a further 75–100m below. While this is easy to plan, the results will be sub-standard as the photographs will lack detail (on the lower benches) and the survey accuracy will be poor.

A solution is to create a terrain-following flight plan where the drone flies at a constant altitude above the surface, ensuring high picture quality and a consistently accurate survey.

TAKING GOOD PHOTOGRAPHS

As for any photography, light plays an important part (by definition) when using a drone. 

Given the drone is moving while the photographs are being taken, you need as high a shutter speed as possible, preferably something like 1/1000th of a second. This is not always possible during the winter or periods of heavy overcast, and it can be important to know how to manually control the drone camera shutter speed to make the best of the light.

Likewise, it’s important to always try to fly with the sun as high in the sky as possible, or in such a way so as to ensure that faces are not left in shadow (easier said than done in winter). A shadowed area cannot be re-created accurately in photogrammetry.

FIXING PHOTOGRAPH LOCATIONS ACCURATELY

As mentioned earlier, there are two basic ways to fix the location of the photographs: either while they are being taken or afterwards.

Our experience is that the best way to determine the locations is as they are taken, using a drone that has a high accuracy GPS receiver (L1/L2) and receives a correction signal (eg Trimble VRS Now or AlldayRTK) while the drone is flying. This is the real-time kinematic – RTK – approach.

So why do we need a correction signal? Isn’t GPS good enough on its own?  The reality, unfortunately, is that it is not. An uncorrected GPS location can drift over time, quite substantially.

The above image plotting the horizontal position of a receiver on a known position shows how much drift can occur, hence the need for correction. The drift also occurs vertically. A correction service works by providing (in real-time) the difference (also called a delta) recorded by a base station on a known point between the GPS location it is receiving. 

It’s important to note that for this to work, the drone must be continuously receiving this signal via a 4G connection (which doesn’t always work in remote areas).

The second approach to fixing the location of the photographs is to correct the positions after the flight. A good example of this is the Propeller PPK solution, which produces excellent results and does not require a correction signal while in flight (we deploy this solution to clients in remote areas).

A variation on the second approach is the use of GCPs, where we create marks on the ground in known locations (they must be accurately surveyed by a surveyor) and correct the photograph locations from these known locations on the ground. The problem is that you need to have a lot of GCPs, and you need to maintain them to ensure that they don’t get buried, overgrown, shadowed, blown up or moved, etc.

While this approach is workable, our experience is that it’s far more time-consuming and error-prone in practice and not one we recommend.

The use of terrain-following (right) allows for a high picture quality and a consistently accurate survey.

STITCHING THE PHOTOGRAPHS TOGETHER

To create a three-dimensional image using a drone, we employ a process known as photogrammetry. This is a technology that has been around a long time but is now greatly simplified by improved technology.

In essence, it works like this: if you can see the same point in at least three different photos and know the location of each photograph precisely, you can determine the location and height of that point. Hence the comment earlier about picture quality – the blurrier or less detailed the photo, the harder it is to use it for accurate photogrammetry.

Once the photographs are collected, they need to be “stitched together” either by you (using Pix4D or AgiSoft software) or by using a cloud-based service (eg Propeller or Drone Deploy) to do the work for you.

The DIY approach makes sense if you really want to control the whole process, but it requires high skill levels and a lot of computing power. While we use this approach for specialised jobs, we would generally recommend that a cloud-based approach is more workable for quarry sites.

USING THE DATA

As mentioned earlier, drones are a great way to collect accurate stockpile data, but they can also be used to provide a much broader set of data that is valuable for site-planning.

One of the benefits of using a platform like Propeller or Drone Deploy (to name just a couple) is that the data can easily be viewed, manipulated, and shared by stakeholders.

Our experience is that of the many platforms that we have tried, Propeller (also known as Trimble Stratus) provides the best balance of features.  We particularly like the fact that it is 3D-only (rather than a hybrid 2D/3D approach), finding this much better for collaboration.

COMPLIANCE

Lastly, you also need to have a standardised approach as to how you are going to manage your drone operations. By this I mean you need to consider the following:

• Drone registration with CASA
• Pilot registration with CASA
• Pilot training (and checks)
• Drone operation Safe Work procedures (SWPs), eg flight planning, flying, quality checking, drone recovery, etc
• Survey accuracy checks
• Flight recording
• Drone maintenance recording
• Checking compliance with CASA rules 

If you haven’t seen it before, software like AirData can be an invaluable way to help improve your compliance. There is quite a lot to know about setting up and running an effective drone program. Hopefully this helps to explain some of the basics, but don’t be afraid to ask if you have more questions.

This article was originally published in Quarry Magazine – click here to view original article.

To find out more, contact Steve Franklin on +61 474 183 939 or steve.franklin@eltirus.com