# Volume measurement problems

Hi all,
I have to measure wood stock piles as you can see in the picture.
The ground is flat so I have to take “linear fit” or “triangulated” as base plane option.
The porblem is that the results are very different and not even close to the real volume. The Volume measured by:
hand is 172 m3
linear fit: 72,6 m3
Lowest point: 168,5 m3
triangulated: 49,4 m3
How is it possible that the results are that different? I flew 40 meter high with side and front overlap of 80%.
Thank you for helping!

It’s good that you ground truthed it. Always a good thing to do to quantify the process.
It looks like “lowest point” works best here since, as you say, the ground is flat. If by chance one or a few of your points were on a log or high point with the other processes you would get less volume. The flat ground with lowest point would would best since that would override the extraneous high point.

I agree with Gary. If the ground is flat, I would not worry about tracing around the pile so tightly. You may very well be grabbing elevations at the top of the pile. Try the moving your boundary away from the pile some.

It does look like some of the points are at least on the side slope. You can use elevation view to see the edges more clearly or the distance measure to tell exactly where it is. What do you get with 6-points and best-fit? Can you share the map?

@f.roecher I would make sure you are using lowest point and making sure when picking your points out you are seeing the lowest point. Like @MichaelL said, I would turn on the elevation layer to see this better.

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@Gary , I am also facing same issues with volume measurement. as per volume measurement document “lowest point” is suitable for stockpile which is against to wall. But, F.rocher the stock piles are completely on flat ground it clear that from image. then , how lowest point is measurement are correct.
One case , its accept to consider closest values but how to ensure in case of multiple stock piles on ground.
please help.

I very rarely use lowest point because even a couple of inches over a large area can be a considerable amount of material (in some people’s eyes), but more importantly I regularly hear on these threads that people are concerned with percentages of the accuracy that can be proven. I have proven countless times that my quantities are within 5% of any of the GPS or Robotic Surveys that I have done in comparison. Under 5,000cy it is more like 3%. When you bust the number by using lowest point 5% can turn into 8 or 10% in a hurry.

I’m not sure if the triangulated base plane has been released or not, but we have been testing and I think there is some definite clarification that needs to be had. I now see another nomenclature called linear that seems to have taken the place of best fit, but there again I do not know if it is released or if there is any difference as compared to what use to be called best-fit.

All that said, taking off stockpiles is an art that is learned by use and comparison. Always verify often at the beginning until you are comfortable. Knowing where to put the points, how many of them to use (don’t waste your time plotting too many) and using tools like the elevation map and distance (and slope) measure tool will allow you to very accurately takeoff any pile in any situation and be confident that you are within 5%.

Note how I found the low point with the Distance tool and did not place another vertex until the other side of the span.

If you have a large delta in elevation you can adjust the slider on the elevation view to make the gradation more detailed. Note how the correctly colored map appears and how the stockpiles on the south end are not very defined.

AND THEN…

Well, speak of the devil. Here’s the official announcment…

Triangulated Base Plane renders more accurate results when measuring volumes on mine sites, long thin stockpiles, or grain bags in a field. Lowest Point enables the volume calculation stockpiles on flat ground, in bins, or for piles that have other piles right up against it. Linear Fit (previously known as “Best Fit”) remains the default measurement option that all types of users leverage for stand-alone stockpiles on flat grounds. Below is an illustration of the differences:

• Linear Fit: defines the base plane by fitting a perfectly flat plane, in 3D, through the chosen edge points.
• Lowest Point: calculates a horizontal base plane from the lowest edge point.
• Triangulated: combines all of the edge points to create a 3D surface under your stockpile.
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I would recommend taking a good look to see if you are being impacted by the systematic SfM doming (elevation) error - if SfM processing techniques are being used.

@James_Dow, Did you seriously just bring up the doming subject again in regards to a stand-alone stockpile?