A lot of first stockpile jobs look easy on paper: fly a gravel yard, hand the client a number. The flight takes twenty minutes. Arguing about the number can take weeks, because nobody agreed up front on where the bottom of the pile was. That is the real lesson of drone stockpile volume measurement: the drone is the easy part. The flight plan, the base plane, and the way you control accuracy decide whether your volume holds up when the yard manager compares it to the scale-house tickets.
This is a field guide to doing it right, from planning the flight to defending the report. If you are earlier in the process and still deciding how surfaces get compared, start with cut-and-fill volumes computed on your own desktop, then come back here for the stockpile-specific details.
What a stockpile volume actually is
A stockpile volume is the space between two surfaces: the top of the pile, which the drone captures, and the base of the pile, which it usually cannot see. Everything in this guide is about getting those two surfaces right.
- The top surface comes from photogrammetry: overlapping photos become a point cloud and an elevation surface (a DSM).
- The base surface is either measured (a bare-ground flight before the pile went down, or a ground surface from an earlier survey) or estimated (a plane built from the ground around the toe of the pile).
- The boundary is the line you draw around the toe. Where you draw it changes the number.
If the client is also converting cubic yards to tons, a fourth input enters the picture: bulk density. That number comes from the client's material testing, not from your drone. Say so in the report.
Plan the flight for the pile, not the yard
A stockpile is a steep, textured shape sitting on flat ground. The flight plan has to capture the sides as well as the top, or the software will smooth the slopes and your volume drifts.
Overlap
Stockpiles are one of the few jobs where it never pays to cut overlap to save battery. A common starting point for volume work is around 80% front overlap and 70% or more side overlap. Uniform material such as sand, fines, or salt has very little texture for matching, so higher overlap gives the software more chances to tie photos together.
Altitude and GSD
Ground sample distance (GSD) is how much ground one pixel covers. Lower altitude gives a finer GSD and more detail on the slopes, but more photos and longer processing. For most aggregate yards, pick an altitude that clears every conveyor, light pole, and loader path with margin, then check the GSD that altitude produces. Write the actual GSD into the report so the client knows what resolution the volume was built from.
Crosshatch and obliques for tall piles
Tall, steep piles hide their own sides from a straight-down camera. A crosshatch pattern (two grids flown at right angles) or a ring of oblique photos around the pile fills in the faces. If a pile casts a deep shadow or has an overhang from a stacker, that is where you will see holes in the point cloud first.
Timing
Fly when the yard is quiet. A loader biting into the pile mid-flight changes the surface between photos. Ask the site to pause work on the measured piles, note any piles that were active, and fly as close to the same time of day as the last survey to keep shadows consistent.
Choose the base plane on purpose
The base plane is where most volume disputes start. There is no single right answer, but there is always a defensible one, and it is the one you picked before you saw the number.
- Measured base (previous surface). If you or someone else flew or surveyed the pad before the material went down, compare the current top surface to that base. This is the strongest option because the base is a measurement, not a guess.
- Toe or rim base. When only one surface exists, the software builds a base from the elevations along the boundary you drew around the toe. This works well on flat, hard pads. It is still an estimate of ground you cannot see, so label it that way.
- Same-flight ground surface. A ground model (DTM) made from the same flight can help on gently sloped pads, but it cannot see under an opaque pile. Under the pile, the ground is filled in by interpolation and may keep part of the pile in it.
Pick the method per site, write it down, and use the same method every time you return. A volume that changes because the base method changed is not a change in inventory.
Draw the boundary at the real toe
Draw the boundary where the pile meets the pad, not where the material thins out into tire tracks. Leave out equipment, stacked pallets, and vegetation at the edges. If two piles touch, decide where the split goes and keep that split consistent between surveys.
Accuracy: control, then repeatability
Precision and accuracy are not the same thing. A volume can repeat to the cubic yard every month and still be off if the whole model is shifted or tilted. Two habits handle both problems.
Ground control points and RTK/PPK
Ground control points (GCPs) are surveyed targets on the ground that pin the model to real coordinates. RTK or PPK (real-time or post-processed corrections to the drone's GPS) tightens the camera positions themselves. Either approach helps; many crews use RTK or PPK with a few GCPs or check points to confirm. What matters for volume is the vertical: a small vertical tilt across a large pad becomes a large volume error. Place a check point you did not use for processing and report how far the model misses it.
Repeatability
Most stockpile clients care about change month to month as much as the absolute number. To keep month-over-month comparisons honest, keep these the same:
- The same altitude, overlap, and pattern.
- The same control points and coordinate system.
- The same base method and boundary rules.
- Roughly the same time of day.
If something has to change, note it in the report next to the number it affects.
Common errors that move the number
- Wet or reflective material matches poorly and leaves holes or noise on the surface.
- Wind on fine material blurs edges and leaves a fuzzy top in the point cloud.
- Vegetation on old piles lifts the top surface. Weeds are not inventory.
- Equipment parked against the toe gets counted as material if it sits inside the boundary.
- Missing control on the far side of the yard can tilt the model, which shows up as a volume error on the piles farthest from your targets.
Doing the volume work on your own hardware
This is where SkyView Desktop comes in. SkyView processes your RGB drone photos into orthomosaics and photo-based 3D on your own Windows computer, so a monthly yard survey does not come with a per-map processing fee. That is our claim and our pricing model, not a comparison to anyone else's.
For stockpiles specifically, the SkyView documentation covers:
- Volume measurement against a second elevation surface or previous flight, against a bare-earth surface, or against a base built from the boundary rim when you only have one surface.
- Batch saved stockpile boundaries, so a yard with many piles can be measured in one run instead of pile by pile, with results saved as CSV, HTML, PDF, and a JSON run record in the project's reports folder.
- Coordinate frame labels that record whether the data is surveyed, declared, or relative, including data controlled with GCPs or RTK/PPK.
SkyView does not certify survey accuracy, and it does not see under a pile. A rim-based base is an estimate, and the report should say so. Those limits are true of every photogrammetry volume, and stating them up front is what keeps the report from turning into a long argument.
After the volumes are done, the rest of the job lives in the same Pilot Ledger account: the quote for the recurring survey, the scheduled flights, and the invoice when the report goes out. You can see how SkyView fits with the rest of the platform on the SkyView page.
A simple stockpile report checklist
- Date and time flown, altitude, overlap, and the actual GSD.
- Control used (GCPs, RTK/PPK, or none) and the check point miss.
- Base method for each pile, plus the boundary image.
- Volume per pile, with tonnage only if the client supplied the bulk density.
- Notes on active piles, wet areas, or anything that limits the number.
When the client would rather hire it out
Not every yard manager wants to learn base planes. If you are on the client side of this and want someone else to fly and report it, read this guide to hiring a drone pilot for stockpile volume surveys. It covers what to ask for and what a good report should include.
If you are the pilot doing the measuring, the workflow above is the whole job: plan for the slopes, choose the base before you see the number, control the vertical, and repeat it the same way every month. When you are ready to process and deliver it from your own computer, see SkyView and Pilot Ledger plans.