Does elevation affect volume calculations

I use a DJI Air 2S. I have been using the default elevation of 49m and overlap of 75/75. I flew my Air 2S over one of our properties yesterday that had a small stockpile of about 250cu m. I know the volume based on the tonnage of aggregate we trucked. The calculated volume was 212cu m. I wondered if the flight elevation was too high for such a small stockpile. Then I wondered if the flight elevation affects volume calculations for large stockpiles in the 3000cu m range. I flew my Air 2S over 3000cum to 7000cu m stockpiles at elevations of 49m and 39m and got different volume calculations based on the flight elevations. My level of comfort with volume calculations has severely dropped. Does the flight elevation affect volume calculations?

Fred Penney 7 de agosto de 2025 15:54

Comentario oficial

Bah! I responded to this a while ago but apparently it didn't get posted. Sorry for the delay.

The Map Pilot Pro defaults are 60m and 80/80 overlap. That comes out to roughly 2.5cm/pixel on most cameras and 80% it what we recommend when you care about the elevation related outputs (like volume measurements).

The volume measurements are not going to change much if the GSD is 1 cm/pixel vs being 3 cm/pixel but overlap can affect it more.

It is better to fly higher and use more overlap than the fly lower with less overlap. Given the same number of pictures you are going to get better results with the higher overlap.

As far as the repeatability of your measurements goes you want to be using lots of dots when drawing your measurement polygons. Think 20 to 30, not 4 to 6. This lets it account for uneven surfaces better and makes it so one bad point doesn't drag the whole measurement down.

Zane 8 de agosto de 2025 02:59

Iniciar sesión para dejar un comentario.

6 comentarios

I tried to pick the same points around the perimeter for each elevation survey, but no doubt the points are different. I have aggregate stockpiles at two sites. At the first site, the volume measurements for a stockpile of 3/4" crushed gravel are 3,485cu m (49m elevation) and 3,763 (39m elevation). At the second site, the volume measurements for a 4" minus rock stockpile are 7,493cu m (49m elevation) and 7,710cu m (39m elevation). I picked lots of points around the base of the stockpiles. Either one of the volume calculations for each stockpile is wrong, or both are wrong. I can't have confidence in the volume calculations given these observations.

Fred Penney 8 de agosto de 2025 12:24 0 votos

Interesting. I guess with the stockpile with the larger rock the GSD might actually matter a bit. Smaller GSD would resolve the top layer of the rock a bit better.

What are the names of the maps and what piles are you measuring?

Zane 8 de agosto de 2025 14:02 0 votos

The stockpile names are Flower Hill Aug 05 2025 and Flower Hill 38m Aug 07 2025 (3/4" gravel) and Botwood Airstrip Aug 06 2025 and Botwood Airstrip 39m Aug 07 2025 (4" minus rock). There were two dump truck loads of 3/4" gravel removed from the Flower Hill stockpile between flights. I estimate that to be around 15 cu m.

Fred Penney 8 de agosto de 2025 17:21 0 votos

I can see the differences you are seeing. I think this is an overlap issue. Since it is a small area and you have the Pro tier you can process up to 150 images for free so use that. Fly at 50 meters and use 82% overlap to give the system a lot to work with. Include an area that is slightly larger than what you are trying to cover so the piles you want are not right on the edge which is an area that just gets less overlap in general.

Zane 9 de agosto de 2025 22:10 0 votos

Okay, thanks. Anytime I need the volume measurement to be very accurate, I will adjust the overlap.

Fred Penney 10 de agosto de 2025 08:58 0 votos