Theory and Practice of Stockpile Volume Calculations Using Drone Data

‘How accurate is it?”
This is the most common question asked by people considering using drones in conjunction with the Propeller platform to calculate stockpile volumes.
Understanding conventional surveying techniques
Using traditional ground-based surveying methods to calculate the volume of a stockpile means a surveyor must take their equipment on site and capture the coordinates and elevation of multiple points — around the base of the stockpile, on top of the stockpile, and along all of the breaklines.
Once these points have been captured, the surveyor can go back to their desk and generate a surface model. This model is compared against previous survey data, or a baseline surface or a virtual reference plane, to calculate volume changes.
Measuring all the stockpiles in a large stockyard using this method can take days to complete. The surveyor is generally exposed to hazardous conditions (walking near heavy equipment, climbing up unstable stockpile surfaces, etc) and it’s often necessary to halt operations while surveying work is in progress.
The alternative: Using drones and Propeller
The more points that are captured, the more accurate a surface model will be — and a drone can capture thousands more points than a surveyor using traditional methods, in a fraction of the time.
As an added benefit, using a drone means nobody needs to scramble up and down a stockpile, and site operations can continue uninterrupted.
By stitching together geo-tagged drone photos with high overlap, captured from multiple angles, Propeller allows users to generate very dense 3D point clouds. While ground-based surveys capture just one point every 2–3 meters, an average stockpile surface within the Propeller platform is modelled using tens of thousands of points.
The result is more precise 3D surface models for higher accuracy volume calculations, safer and faster than before.
How it works in practice
Let’s say, for example, you want to find how much material has been added or removed to a stockpile since your last drone survey.
Simply select the Polygon tool inside the Propeller platform, and draw a line around the base of your stockpile. In an instant, Propeller will ‘take’ the thousands of recorded height samples within the boundary of this polygon. Conceptually, this is similar to a surveyor climbing across a stockpile taking thousands of elevation points — though clearly much safer!
Next, Propeller compares these height readings (from your current survey dataset) to those from your previous survey (at exactly the same horizontal locations). Volume changes are expressed as either positive change, where material has been added (labelled ‘Fill’) or negative change, where material has been removed (labelled ‘Cut’).
You can also see the ‘Net’ change (Fill+Cut). A record of these values over time can be easily exported for reporting purposes.

It’s also possible to view changes in stockpile volumes as a cross section. In this case, Propeller reads the recorded height samples from various distinct datasets along a line that you have drawn, and renders the results on an interactive chart.

Best practices for volume measurements using the Propeller Platform
Our internal testing has found that ‘tight’ polygons around stockpiles produce the most accurate volumetric results.


So, when drawing your measurement polygon, it’s best to stick to the edges and not go too broad. If the edges of a stockpile are difficult to see, turn on Contours view in the Layers menu for extra visibility.
Once your polygons are well-defined, we recommend using the ‘Promote to site level’ feature to save those exact boundaries for use across all future surveys.

This will ensure your volume calculations are accurate and repeatable.
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