ORTHOSFall is when most aggregate yards and quarries start caring about pile counts again — year-end inventory reconciliation, loan collateral audits, and closing out the season's production numbers all land in the same few months. And most of that still gets done the same way it's been done for decades: someone walks the yard with a wheel or a GPS rover, eyeballs the pile shape, and writes down a number that's close enough.
"Close enough" is usually fine until it isn't — until a lender wants a number they can trust, or the loader operator's count and the office's count are 8% apart and nobody can say which one's right. That's the actual question worth answering: how accurate is a drone survey compared to what you're doing now, and is the difference big enough to matter for your yard?
What "RTK-accurate" actually means
RTK stands for Real-Time Kinematic — a GPS correction method that uses a fixed base station to correct the drone's position in real time, instead of relying on the raw GPS signal a phone or consumer drone uses. Raw GPS is accurate to somewhere between 1 and 3 meters. RTK gets that down to roughly 1-2 centimeters horizontally and 2-3 centimeters vertically.
For a stockpile survey, vertical accuracy is what actually drives the volume number — a pile's height is what you're really measuring, not just its footprint. That's the gap between a drone flight that's "roughly right" and one that produces a number you'd put in front of a lender.
How the three common methods actually compare
| Method | Typical vertical accuracy | Time on site |
|---|---|---|
| Walked estimate / eyeballed | ±10-20% or more | Minutes, but subjective |
| Consumer GPS handheld unit | ±1-3 meters | 30-60 min per pile |
| Traditional ground survey (total station) | ±1-2 cm | Half a day or more, per site |
| RTK drone photogrammetry | ±1-3 cm | 10-20 min flight, whole yard |
The honest comparison isn't "drone vs. nothing" — it's drone vs. a traditional ground survey, since that's the other method that actually produces a defensible number. RTK drone photogrammetry lands in the same accuracy class as a total station ground survey, but covers an entire yard's worth of piles in the time it takes to survey one pile by hand.
Why this matters more in fall than in spring
Three things stack up this time of year: production volumes are at or near their yearly peak, year-end reconciliation is coming, and weather windows for a clean flight start narrowing as fog and rain move in. Waiting until January to get an accurate count means reconciling against a number that's already a few months stale.
A recurring monthly flight through the fall gives you a paper trail — each report shows what moved since the last one, so by the time year-end numbers are due, there's no scramble to figure out where the season landed. If the same trip covers more than piles — say you also need a current property map for drainage or expansion planning — that's usually worth bundling into the same visit.
What you actually get in the report
- Per-pile cubic yardage — broken out individually, not one blended number for the whole yard.
- RTK-corrected accuracy — the same class of precision as a ground survey, without a crew walking every pile.
- Month-over-month comparison on a recurring schedule, so movement between flights is visible, not just the current total.
Frequently asked questions
How accurate is a drone stockpile survey compared to a ground survey?
RTK-corrected drone photogrammetry lands in the same accuracy class as a traditional ground survey using a total station — roughly 1-3 centimeters vertically — while covering an entire yard's worth of piles in the time it takes to survey one pile by hand.
How often should stockpile volumes be measured?
Monthly is the standard interval for an active yard, since it builds a month-over-month record that lines up with inventory reconciliation and year-end reporting instead of a single stale snapshot.
Can a drone stockpile survey be used for lender or collateral documentation?
The RTK-accuracy volume figures are suitable for internal reconciliation and most reporting needs. Check with your specific lender or agency on their preferred format before relying on it for a formal audit.
Orthos Aerial Group runs RTK stockpile volumetric surveys across the Sacramento Valley — Redding to Sacramento — for aggregate yards and quarries reconciling inventory this season.