No matter what industry you’re working in, measuring and reporting on your stockpiles is crucial to successful operations.
But before you can take a single measurement of your stockyard, you need to fly your drone to capture site data. There are a few ways to do this. “Drone surveying,” at its core, means using a drone to take aerial photos of your site and some form of GPS and ground control to tie the images down.
With recent technological advancements, there are two major workflows to get the job done: GCP-based drone surveying and PPK drone surveying.
Drone surveying with traditional ground control
For this workflow, you need a sufficient number of known points to verify and pin your drone imagery to the ground because a drone without on-board GPS correctional processing capabilities is only a vehicle for capturing site imagery.
Having multiple GCPs on your site when surveying ensures survey-grade accuracy, but they can be time consuming to set up on a large worksite. There are a couple of ways to set up traditional ground control:
- Known-point method. A surveyor has to physically walk your site, shoot the points with a rover, and mark them for visibility.
- Using AeroPoints. AeroPoints are smart GCPS you drop in an optimal distribution across the entire surveyed area.
As recently as a few years ago, the planning, risk assessment, and legwork associated with setting up ground control has been a necessary, if unwanted, sacrifice.
Drone surveying with onboard GPS correctional processing changes the need for ground control
PPK drones are able to accurately geotag and correct their GPS data. While there are different kinds of GPS correctional processing technology, we’ll be covering PPK here.
(If you want to learn more about RTK, check out our Drone Surveying Explained: From GCPs to PPK ebook.)
PPK stands for “post-processing kinematic.” With PPK capability, the drone geotags X, Y, and Z coordinates to each images based on its GPS unit. While this happens, a base (be it a base station, an AeroPoint, or the CORS network) on the ground is also recording positional information, but with much more accurate triangulation.
After the flight is completed, those two sets of GPS data are matched up using the timestamp recorded when the drone takes a picture. Now that we know the offset after the fact, the initial, less-than-accurate on-board GPS data can be overwritten, giving precise geotags for the imagery.
Due to its ease-of-use and reliability, we recommend a PPK workflow for drone surveying on any site—from mines to landfills and every construction site in between. Propeller PPK, our workflow that requires only one AeroPoint, gets 1/10ft accuracy.
Drone photogrammetry: turning your site data into a 3D survey
When that data is processed into the final product—a 3D site survey—powerful processing engines are crunching numbers for many, many images and using photogrammetry to stitch them all together.
At its most basic, “photogrammetry” is measuring via photos. Essentially, if you see the same feature from three or more known positions, you can triangulate its location in space (get those exact X, Y, and Z coordinates). A feature is any visually distinct point in an image.
The more features you match, the better you can relate images to each other and reconstruct objects within them. This is exactly what photogrammetry software does for one feature, and the next, and the next, and so on, until it’s covered your entire site.
Once you have a lot of these features—think millions—you create a “cloud” of points. Each point has a matched feature describing your surveyed area in that location. You can then turn your point cloud into any regular outputs used in geospatial software, like a 3D mesh or digital elevation model (DEM).
Get the right hardware for drone surveying
Picking a the right craft can be overwhelming, but when it comes to drone type, price, camera capabilities, availability, and ease of maintenance, we’ve found DJI’s Phantom 4 Pro to be the best for most site surveys, or its PPK counterpart, the Phantom 4 RTK.
Phantom 4 Pro drone
Phantom 4 RTK drone
With the exception of some size-related edge cases the Phantom 4 Pro or Phantom 4 RTK gets the job done right at a lower price point. DJI drones are widely available and mass produced. This means they have an ease of maintenance that custom or fixed-wing drones lack.
As with any other worksite tool, it’s best to avoid providers who cannot guarantee quick repairs or replacements. You don’t want to postpone your surveys because you’re waiting on a replacement drone or part.
Download our ebook on stockpile measurement and reporting to learn more.