Trying to eyeball the volume of a pile of sand or gravel is a bit like guessing how many jellybeans are in a jar — if the jar were gigantic and irregularly shaped. Yet many construction companies and aggregate suppliers rely on eyeballed guesstimates, perhaps performed with the help of a yardstick, to drive business decisions. Others make significant investments in ground surveying.

That’s where drones for volumetric analysis come in. “With the drones, we can fly over and measure the volume of each pile so the contractors know exactly how much they have,” said Erica Stein, drone program lead for the Advanced Solutions group at United Rentals, which provides end-to-end drone services.

Measuring stockpiles via drone mapping is fast and efficient. It takes as little as 30 minutes to an hour for the done to capture multiple photos of an area. In a process called photogrammetry, specialized software converts the photos into a highly accurate 3-D map showing the boundaries of the pile and multiple data points for its different heights. The software calculates the volume of the pile based on this information. 

United Rentals estimates that its drone service can provide stockpile measurements that are accurate within 5 percent and allows companies to measure inventory about twice as fast compared with ground surveying.

By comparing the data generated from the drone’s weekly or bi-weekly flights, a company can not only know how much material they have but also track how much they’re using and how fast they’re using it.  

One United Rentals customer, a large supplier of construction aggregates, was having trouble measuring and tracking its multiple stockpiles of various aggregates in a 10-acre stockyard. “They had no good way of knowing when the materials are used, when the piles are moved or how fast they go through the materials,” said Stein. As a result, they were handicapped when it came to making accurate bids and also managing inventory. “They don’t want to have excess, but they also want to have enough for other jobs,” said Stein.

Drone mapping changed the equation. “In the portal, they can view what the volume was on the last date vs. the previous week so they can know how much material is being used, they can bid jobs more accurately, and they know how much they need to order,” said Stein.

The company has multiple sites, and United Rentals has bundled some of them together so that, as Stein noted, “all the sites can work together and the information will be accurate across the board rather than one site performing measurements one way and another site doing them another way.” The ROI of the drone service has been so significant that the company is aiming to make the technology a standard for all of its sites. 

There’s a safety benefit as well: Using drones keeps workers out of the piles and away from equipment that could be on its way to move them. 

Freelance writer Mary Lou Jay writes about business and technical developments in a variety of industries. She has been covering residential and commercial construction for more than 25 years.