The use of drones and other unmanned aerial systems for stockpile calculations is quite common these days.  The UAS flies a grid pattern over the stockpile area and georeferenced images are stitched into a three dimensional point cloud prior to volume calculation.  Some would argue that volumetric calculation via drone only involves relative accuracy and doesn’t need to be “truthed” to real-world/absolute ground control point data.  That said, others have found it necessary to have a GCP survey done prior…