Accuracy: different heights for different flights


#1

I’m not sure if it’s been discussed or not, and I’m very new to the forum, but here goes.
Would it make sense to fly the same area at different heights on the same day to get even more accurate volumes of aggregates at our gravel pit?


#2

I don’t know if I’ve seen a discussion about that on here. I think you’d get a slightly more accurate DSM and 3D model if you had imagery from a few different altitudes, similar to if you flew with an oblique and nadir camera.


Camera best practices for volume calcs
#3

It would depend on your accuracy requirements.
But for the short answer, yes you would certainly achieve higher accuracy.
Another thought would be to do a circular pattern and manually aim the gimbal/camera with a horizontal axis to achieve more detail.


#4

Ya, that would make sense. At the pit, a couple of the piles have straight (or very close to vertical) faces. Another option, I suppose, would be a ‘point of interest’ mission on each of the piles. The piles of aggregate vary in size, but the largest would be roughly 100m long, 40m wide, and 12m high. Thoughts on ‘point of interest’ for volume calculations?


#5

From what I’ve seen, the POI tool gives a lot of images, which can be overkill and add processing time for volumes. Better to take a few well placed images manually that give a good perspective of the area of interest.


#6

Thanks for the advice, I’ll keep all this in mind when I fly them this weekend. I will try flying two missions at different altitudes.
Thanks again.


#7

I’ve talked to customers who had good results by flying one overhead mission high altitude (depends on site, but say 200 to 300 feet) + another mission a bit lower or up to half the AGL of the first flight (so using this example, 100 to 150 feet) + plus a few manual pix. This takes more effort and batteries, but can give that clear, high-level context data plus nice data at a lower altitude to increase accuracy of volumes.

Good luck and let us know how it goes!


#8

Would you do this at a low altitude?


#9

What are most people seeing for accuracy in there maps and are the clients happy with the accuracy results?


#10

We’ve gone down to 30m on quarry stockpiles, normally at least two heights (depending on local terrain - sometimes on a deep quarry we need 3) and depending on the size of the stockpile and sheer angle we’d also add oblique imagery. Basically, both GPS and ortho imagery lack resolution on the vertical. You need to add this height information somehow to get accurate volumes and the techniques @Lidar and @neema have mentioned will do this.


#11

I flew a number of quarries at half year for stock takes. The trial site with a stock heap of known volume was flown at 75m high and the results were within 2. I did one site where stocks were at different levels and tricky to break the flights up. In this case some parts were at 35m whilst others at about 90m. Again results were in line with expectations.


#12

I’m finding amazingly accurate volumes. in general I fly 200ft with 80x80 overlaps. Gives me about 35 angles on every square inch of the area to be mapped. Again, amazingly accurate on stockpiles. Some are verified by scale and we have consistently seen less than 1% variation to scale tickets. One such pile we were .006% off.


#13

Hi everyone, sorry if the question that I am about to ask, has been asked before.

When planning a flightpath for doing stockpile measurements, is it better to just have a normal flight path, i.e. one direction only, or will you get more accurate readings if you do a Crosshatch with the camera pointing down at 90°? Would there be a difference in the output accuracy between 30m and 50m altitudes, if say both sets of images were clear and with no motion blur?

Thanks for your input.


#14

If the stockpiles are smaller than 10000cy I wouldn’t waste your time. If close to that size or larger, or if there are many piles of different types of materials clumped together then run structure mode. Your real accuracies will be reliant on your base plane.


#15