Using scale bars for Pile volume measurement

[wizprod]

Hi all,

Currently evaluating Photoscan as a tool in my UAV business.
I don't have access to RTK precision GCP eqiupment, but I do have a very accurate Laser range-finder. Can I use that in combination with coded targets and scalebars instead of a RTK GNSS solution?
What will the precision be compared to RTK, if I can measure the scalebars to within 1 mm pr 10 meters?

[Hydro_Ydé]

How do you fix height with your distance meter ? This job needs a lot of known xyz points to be accurate.

[JMR]

If you can measure 3 or more long distances and your works are solely aimed to volume estimations, then you can probably get same accuracy as withe 3D ground control points. However you should be careful avoiding extrapolated areas that are far from the area enclosed (more or less) by your distance measurements.

[wizprod]

How do you fix height with your distance meter ? This job needs a lot of known xyz points to be accurate.

Well, that's part of my question

[wizprod]

If you can measure 3 or more long distances and your works are solely aimed to volume estimations, then you can probably get same accuracy as withe 3D ground control points. However you should be careful avoiding extrapolated areas that are far from the area enclosed (more or less) by your distance measurements.

My primary purpose would be to measure the volume of a given stockpile. I might throw in the 3D render & orthomap, just for extra content, but not something customer expects nor requires.

So if I layout 6-8 point around the pile, and do as many measurements between those 8 points as possible?
Of course I will still use the GNSS on the drone combined with the scale-bars. From whitepapers on the subject, it seems that some of the position inaccuracy can be averaged out by very substantial overlap (>90%).

Interestingly enough, Dronedeploys guide on stockpiles actually explicitly say that GCP's are not needed: https://support.dronedeploy.com/docs/volume-measurement

What is Your guys experience with that?

[JMR]

that's what I said. drone deploy is right. GCP are not strictly required for stock pile measurements... but a few distances are a must if you want obtain decent quantity numbers.
Do the same pile volume estimation from two different flights without using scale bars and you will probably find out that quantities can change quite significantly from flight to flight

Once you add good scale bars, the role of on board gnss will become mostly negligible. keep in mind that by default camera positions are supposed to be as accurate as 10m, while scale bars are usually supposed to be in the range of a few mm accurate.
Lastly I'd kindly suggest you that as long as you don't want or can't afford to use surveying methods for ground control, do not give away any so-called "orthomap", not even as extra... or if you do so, please call it mosaic, or collage, or whatever that is far enough from surveying & mapping glossary...

[wizprod]

that's what I said. drone deploy is right. GCP are not strictly required for stock pile measurements... but a few distances are a must if you want obtain decent quantity numbers.
Do the same pile volume estimation from two different flights without using scale bars and you will probably find out that quantities can change quite significantly from flight to flight

Once you add good scale bars, the role of on board gnss will become mostly negligible. keep in mind that by default camera positions are supposed to be as accurate as 10m, while scale bars are usually supposed to be in the range of a few mm accurate.
Lastly I'd kindly suggest you that as long as you don't want or can't afford to use surveying methods for ground control, do not give away any so-called "orthomap", not even as extra... or if you do so, please call it mosaic, or collage, or whatever that is far enough from surveying & mapping glossary...

Thank you very much for your time and explanation. I will go out and do some tests in the weekend.

[SAV]

Hi wizprod,

If you are only interested in the volume, it should be fine to just use scale bars. However, make sure that they have an 'adequate length'. For example, if your survey area is 500m x 500m, you probably shouldn't use 1m scale bars. I would normally just place markers/GCPs on the ground and then use a long tape measure to acquire the distance between them.

Alternatively, get a low-cost RTK/PPK GPS like the Emlid Reach RS which has shown to deliver accurate measurements.
https://emlid.com/reachrs/

All the best.

Regards,
SAV

[wizprod]

Thanks! I will try out a few things !

I have been looking at the Emlid solutions for a while, might pull the trigger at some point.

[SAV]

Hi wizprod,

Emlid has released a new Reach+ which will be available in May 2018. Wait a few more weeks until you pull the trigger ;-)

Regards,
SAV