Here are some photos from Feb 2017 of a stockpile that I flew with a Phantom 3 Standard. This flight was done at 120’ with 80%/80%, straight down camera doing a gird pattern (Pix4D) and processed in DroneDeploy.
I use these photos to show how drones can get better results than a traditional topo of this type of site. I show the washouts and ask the surveyor a simple question “How would you topo this”, their answers is always “do a cross section” (TOB, Flowline, TOB) every 50’ or so.
In these photos you can see a great 3D model of the stockpile that was able to look down inside the washouts (you can see this in the elevation photos) which means it can do a volumetric with them.