Out of the Field: How to Measure Grain Stockpiles with a Drone

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With the current volumetric software available, it becomes fairly turn-key to measure grain stockpiles with a drone to garner bushel estimates for planning and forecasting purposes!


Curt
Nov 7, 2016

Thanks to some much needed drought busting rains this growing season, we’ve had bountiful crop harvests here in Western Kansas.  With slumping grain prices providing no motivation to sell in the current market conditions, our elevators have a glut of grain on their hands. As per the common practice to deal with overages, area Co-Ops have resorted to stockpiling grain as the elevators top off.  Make no mistake – this is a rare occasion in our dryland neck of the woods with limited moisture!  Our local Co-Op, Midland Marketing, started amassing a pile of sorghum recently at their Yocemento, Kansas, elevator (My ninety-one year-old grandfather will tell you that to his recollection, this is the first time he’s witnessed stockpiling at that location!).  As my family progressed with fall harvest, this provided the perfect opportunity to fly, map, and measure grain stockpiles with a drone; which certainly beats throwing the drone in the closet for the winter!

Doing it right: Flying the location

If you’re going to measure grain stockpiles with a drone, the first thing you have do is find a stockpile! Arriving at the previously-mentioned overflowing elevator with drone in-hand, my first stop was the elevator general manager’s office to ask for permission to fly the property.  After explaining my plans, he was enthusiastic to compare my results to his “guesstimate” of 120,000 bushels for the current state of the stockpile.  With the manager’s okay, I proceeded to chat with the folks running the grain handling equipment to make them aware of my intentions and ensure that my flying a UAV in the vicinity wouldn’t hinder what they were doing.  It also bears mentioning that because of the way this Co-Op handles grain unloading, the drivers of the grain trucks did not leave the cabs of their trucks (Part 107 compliance in full effect!).

How to get the best 3D!

Although not always necessary to measure grain stockpiles with a drone, I decided to acquire oblique images to improve my 3D model.  Is this needed for accurate stockpile measurements?  Not so much (at the time of this writing, anyway), but it certainly increases the “gee-whiz” factor when showing flight products to clients and other decision-makers interested in drone mapping technology. If we’ve got the time and the battery to do it, we always make it a point to run a quick orbit or two around the stockpiles, terrain, structure or any other feature that may benefit from extra relief and visual detail. When uploading the mapping mission images to DroneDeploy, all you have to do is include the oblique images form the second flight in the photo pile to be uploaded and DroneDeploy will handle the rest.  Need to know best practices? Get them straight from the horse’s mouth for optimal results!  

Measuring and profiling: Where the rubber meets the road.

Once a flight has been processed, a variety of deliverables and tools are available with most image processing software and services. As our business is a DroneDeploy partner and service provider, that’s what we’ll be using for our ad-hoc study.  If you’re going to measure grain stockpiles with a drone and you’re looking get an idea of “how much” of a particular commodity you have, you can grab that calculation with the Volume Measurement tool while viewing the Elevation map.  Why use an elevation map when we’re looking at volume?  Simply put, we’ll be treating this big ol’ stockpile as a land feature (think: “Mountain of grain”). Per best practices for use of the tool, we want to begin measurement from a level plane around the base of the subject to get better accuracy of our calculation. In short, flat and level around changing terrain acts to “zero the scale”.

Once you’ve drawn a polygon around your subject, the tool provides a volumetric measurement that is equal to:

  • Cut –  The amount subtracted to make your polygon plane level
  • Minus Fill – The amount added to make your polygon plane level).  

The volume provided by DroneDeploy is given in cubic yards which will need to be converted to bushels by multiplying it by 21.6962 (Google can be your friend as well :-)).  Curious about the height of that stockpile as well?  Use the distance tool to measure the across the pile to see length and relative profile height.

measure grain stockpiles with drone cross-section

Accuracy – Good enough for some?

As is especially the case when talking to folks that measure and survey for a living, the accuracy of measuring grain stockpiles with an off-the-shelf drone can be called into question. Is the measurement really useful, or are we essentially performing a really neat-looking fool’s errand with no real value? The simple truth  is that the drone-acquired data with no correction is not going to be as accurate as flights processed with ground control points acquired by a survey.  With that said, DroneDeploy has reports of it being within 1 to 2% of professional survey readings. There are also obvious safety concerns that come along with sending folks atop and around fluid stockpiles to measure. Plus, given that many Co-Ops are bootstrapping volumes based on ticket totals anyway, measuring grain stockpiles with a drone yields a valuable comparison of those ticket numbers for elevator managers that they wouldn’t have anyway.

How’d you do? Share your results!

Are you going to measure grain stockpiles with a drone this fall?  Do you have other uses for volumetric calculations?  Whether you have questions or interesting use cases, we’d like to know how you’re flying and what your results are, so feel free to join us in the forums and share!

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