Hi guys, I've been using my P4P for mapping sites that have gravel piles. Using Drone Deploy we are able to accurately map the sites and calculate the size of each pile. Accuracy is extremely good and is saving our client a lot of expense!!
I agree that scale bars are a quicker way to achive more accurate relative accuracy. however any volumetric calculations I am involved with as a surveyor always requires a pre and post survey, or before and after. This makes GCPs an absolute necessity since without them you can not achieve repeatability since the built in drone gps is not accurate enough. Without GCPs I have seen shifts of more than 3 feet between seperate flights of the same area flown with the same drone, even if flights are from the same day. I am very curious about the claim of 98% accuracy since I have never seen anything that close without GCPs and oblique imagery. Even with GCPs when I only use nadir imagery I see much more than a 2% variation. I have been planning a case study to document this type of scenario and get some hard figures and a comparison cross-section but have not had enough time of lately to actually get out into the feild and complete it.GCPs are important. In this case since it is not necessary to georeference, since if I have not misunderstood, it is only to calculate volumes. Good accuracy can be obtained by providing two manual scales with the sole objective of geospatially determining the actual size of the piles. It's faster and easier
It seems that every case study I have found about this subject uses accuracy percentages or only checks accuracy on checkpoints as reported by pix4d or a similar program and never gives hard numbers like a surface being off "this many inches" or compares a traditionally suveyed stock pile to the drone data.
I have now seen 2 polished and 1 rough precise gnss setups for dji RTF craft that are designed to give centimeter accurate geotags that can be PPK'd to adjust for global accuracy. Throw in a couple GCPs for ground truthing and you should be pretty good.
The advantage of PPK over RTK with drones is the needed live connection from the base or CORS to the rover. Eventually I'm sure this will get addressed. But right now it is problematic. Also, CORS logs are a slight bit more accurate than live CORS corrections from what I have read.