Drone or fixed LiDAR? A practical comparison for stockpiles

We get this question once a week: "We need to measure our stockpile — should we hire a drone or install a fixed system?" The answer is usually "both, but not at the same time" — and the key is what you intend to do with the data.

What a drone survey can do

An experienced pilot flies a 5-hectare pile in 60–90 minutes, delivers a point cloud with sub-centimetre node spacing and a volume figure within 1–3 % with a surveyed ground-control network (3–5 % without one) at a resolution a fixed sensor will rarely match — we routinely cross-check drone data against our terrestrial Riegl stack, which is the sub-percent reference. You get one photograph per job. If you need that photograph again in two weeks, we fly again.

What a fixed OWL EYE® STOCKPILE installation can do

The same pile, every few minutes, around the clock, without anyone on site. Accuracy is ±1 % — better than a photogrammetric drone flight and second only to a survey-grade terrestrial laser scan (under 1 %). In return, latency is minutes instead of days, and the volume curve streams straight into ERP.

When the drone wins

• One-shot need. Annual inventory for the auditor, due diligence ahead of a sale, hand-over survey to a new operator. A drone campaign in northern Germany costs a manageable mid four-figure amount per site. A fixed installation does not pay back for a single annual measurement.
• Complex geometry without a sensor location. Long piles, multiple shadowed areas, no workable mast or roof position for an optic. A drone just flies over the geometry.
• Survey-grade accuracy required. When the auditor asks for >99 % in writing, the terrestrial survey variant with the Riegl VZ-1000 is the answer. We offer that as a separate Bulk Inventory service.

When the fixed installation wins

• Piles that change daily. Active production piles, with material in and out several times per shift. A drone scan would be three days stale.
• Dispatch needs the number in ERP. A drone campaign delivers a PDF that someone has to type into SAP. A fixed installation streams OPC UA straight into the ERP loop.
• Closed-loop material control. As soon as the volume measurement feeds back into a control loop — throttling the feed, pulling a shift forward — a weekly drone survey is too slow.

When both win

This is the most common case in practice. The fixed installation runs day-to-day operations; once a year a drone flies a reference inventory and calibrates the fixed system against survey-grade truth. We have run this combination with several customers for years and it is the simplest way to get the best of both worlds.

A rule of thumb

If you need a volume figure less than twice a year, hire the drone. If you need one weekly or more often, install the system. If your dispatch acts on it daily, the drone is just the annual reference check.

Both options live at /stockpile/ and /drone-survey/ — or write to info@sachtleben-technology.com with your pile size and the measurement frequency you want, and we will recommend the right one.