G-Man, it is all done with stereo photography. No lasers or smoke and mirrors. We shoot three exposures of a pile of whatever, only the middle exposure is right over the pile. There are big white X shaped targets on the ground that a surveyor gives us a X, Y & Z location. We then lay in the base terrain map or we can assume the ground is flat. The software we use brings in all the images and while wearing 3D glasses the image has depth. Think of Avatar only working with 3 gigs of data for just one image. It is easy to measure the elevation of any point. Working in one or two foot intervals the software calculates the overall volume.
I found this link with a story about the process.
LANDFILLS: Photogrammetry Digitally Calculates Landfill Volume
The process has been around for years, even before computers.