Volumetric Deliverable

r62ewa · Jun 21, 2017

Has anyone completed volumetric calculations for a client? Was it a requirement to have the volumetric calculation signed off by say an engineer, surveyor or other authority to guarantee accuracy?

I have a possible contract to produce volumetric calculations of rock stockpiles and was curious how others have delivered their volumetric products and what QA/QC was involved?

Pipeliner_USA · Jul 6, 2017

I'm a licensed engineer and surveyor with a drone business on the side and I've never heard of something like a stockpile needing an engineer's stamp of approval. If it does, that must be some QA/QC requirement by a contractor. Your calculations are only as good as the person doing them so show your work and provide all backup information in a way that people can understand, not just a gibberish flight log text file or what have you.

r62ewa · Jul 6, 2017

Thanks, I spoke with the client and they do not need any stamp from an engineer or such. Their requirement is for the relative accuracy to be good as they said they can tolerate a 100mm difference between the floor and stockpile.

Every model I have generated thus far has been at approximately 200 feet elevation flight grids so my GSD is quite small and the accuracy has been very good from doing some ground truthing measurements.

I also plan to include some non-RTK GCPs for which I'll accurately measure on the ground to include in my Pix4D workflow as you can introduce Scale Constraints into the Point Cloud in this manner to ensure the point cloud has high relative accuracy compared to real world measurements.

Thanks for the feedback.

Pipeliner_USA · Jul 7, 2017

Cool. Since it's piles of stone, I'm guessing it's fill material as opposed to excavated material, although I don't know what part of the country you're in. What's the application exactly? They just wanna compare volumes to what the bid said so they don't overspend?

A VERY easy mistake to make when measuring stockpiles is to not define your base well enough, or to call some fixed plane / shape your base... errors add up quick when that's wrong. Get plenty of ground data well beyond the pile.
Also if it is indeed fill that was brought in and piled it wouldn't hurt to ask around for the load tickets...some kid may have all the tickets in his lunch pale and that would give you the real volume, minus any voids/compaction errors too.

r62ewa · Jul 7, 2017

Thanks. It is crushed stone stockpiles they use for surfacing gravel roads and they conduct volumetrics every year or so to compare the pile size current to what it was initially.

I have done one as a test site and compared it to what the Surveyors had calculated, as the client used Surveyors in the past, and my calculation was within 1% of what they had calculated.

Pipeliner_USA · Jul 8, 2017

r62ewa said:
Thanks. It is crushed stone stockpiles they use for surfacing gravel roads and they conduct volumetrics every year or so to compare the pile size current to what it was initially.

I have done one as a test site and compared it to what the Surveyors had calculated, as the client used Surveyors in the past, and my calculation was within 1% of what they had calculated.

Close enough for government work!

With The Birds · Jul 8, 2017

I'd check a few more with the surveyors reckoning for comfort. Within 1% was likely a fluke,

r62ewa · Jul 8, 2017

With The Birds said:
I'd check a few more with the surveyors reckoning for comfort. Within 1% was likely a fluke,

Let's hope not a fluke and something I can replicate everytime, wouldn't that be great. It was a very nice point cloud and model. I also took some of the outputs and processed them in my GIS and made some nice maps overlaying the mosaic on a generated hillshade, it turned out really nice. I also included some cross-section profiles. The client really liked the output in this form.

Richard R · Jul 8, 2017

r62ewa said:
Let's hope not a fluke and something I can replicate everytime, wouldn't that be great. It was a very nice point cloud and model. I also took some of the outputs and processed them in my GIS and made some nice maps overlaying the mosaic on a generated hillshade, it turned out really nice. I also included some cross-section profiles. The client really liked the output in this form.

I doubt that the surveyors would certify their results to within 1% of true! Check with them, but I bet that they specify something like +- 5% maybe even 10. Just too many variables that they couldn't directly or adequately measure. Just trying to climb a gravel pile to measure would change the shape. And if you take multiple measurements of the same pile setting different borders, you will probably get similar variation in your results.

r62ewa · Jul 8, 2017

Richard R said:
I doubt that the surveyors would certify their results to within 1% of true! Check with them, but I bet that they specify something like +- 5% maybe even 10. Just too many variables that they couldn't directly or adequately measure. Just trying to climb a gravel pile to measure would change the shape. And if you take multiple measurements of the same pile setting different borders, you will probably get similar variation in your results.

All very true and good points. The 1% comparison was between the volume I calculated of a specific stockpile which was compared to the volume calculation the surveyors generated for the same stockpile. Our final volumes were within 1% of each other which gave myself and the client confidence in the accuracy of volumetrics that can be generated using UAVs.

Pipeliner_USA · Jul 8, 2017

r62ewa said:
All very true and good points. The 1% comparison was between the volume I calculated of a specific stockpile which was compared to the volume calculation the surveyors generated for the same stockpile. Our final volumes were within 1% of each other which gave myself and the client confidence in the accuracy of volumetrics that can be generated using UAVs.

Did you guys factor in any compaction or air void based on the size of the aggregate? The more I think about it I have to agree with the poster who said meeting the surveyor's calcs to a 1% margin of error is kinda crazy and perhaps coincidental, unless you did a bit of postflight manipulation.

r62ewa · Jul 8, 2017

Sorry guys, I don't mean to mislead anyone. I told the client my volume calculation and he compared it to what the surveyors had done and he stated it was within 1%. I have to admit there was no compaction, air void or other factors taken into account. The 1% was what he said in a telephone conversation.

Richard R · Jul 8, 2017

Perfectly acceptable that measurements by 2independent approaches were within 1% of each other. Just don't mistake that to mean that either measurement was accurate to that degree. It would help to strengthen your case if you could compare the 2 over several measurements both of this and other stockpiles. Even making several separate measurements of the same pile would help you build up some statistical variance info for your methodology. The better you can support any measurement will help build customer confidence in your product.