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Underestimated elevation change and stockpile volume

Hello. Interesting problem here mapping a 1.7-acre area to obtain soil stockpile volumes.

We used the default height (60m) and overlap (75/75) on this flight. Stitched image looks good, but the elevation change between the surrounding surface and height of the piles (and consequently, the volumes) was grossly underestimated. The highest point of the piles is easily 30ft but the mapped change in elevation from the perimeter area to the highest point of the piles was 2ft.

I've read that 80/80 overlap is recommended, but given that 75/75 isn't that far off, should that make this much of a difference? Here's the overlap report image. I assume the white spaces are no data at all? If that's the case this doesn't look great. 

Were we flying too high? I've read that the height should be "at least" 4-5x the height of the tallest feature in the mapped area. Were we too high at 60m? (30ft x 5 = 150ft or 45.7m) I don't quite understand how the software is able to model terrain from these images, but is it possible that we were flying too high for sufficient resolution needed to process the overlap and get those elevations? 

Another possibility I read about was homogeneous colored surfaces. Could the tarps have been the problem here? 

Thanks for any thoughts you may have. 

Neil Curri

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The height is fine but the overlap setting is not. It is super important to use AT LEAST 80% overlap any time you care about the accuracy of the elevation related data products which is what the volumes are derived from.

Also... The Mavic Air does not have a great camera so you need to use even more overlap. I would recommend using 85+% for this small of an area. 

The flatness of the model is related to the low quality camera. Also, if you didn't already, be sure to use Map Pilot in Active Connect mode to get the best data possible. 

Zane

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