So I noticed there’s RMSE numbers now. I flew a site at 1.1in/pix GSD both Nadir 70% sidelap and 80% frontlap, and obliques in a criss cross pattern at 60% sidelap 70% frontlap which isn’t really required but helps improve accuracy.
THe RMSE numbers I got are:
So these are obviously absolute position accuracy numbers - which don’t really help me much as everyone with half a brain knows GPS accuracy for most Drones (or any other GPS device) is typically in the 3-8ft range.
What most end users are interested in is knowing how accurate their distance and volume measurements are. I would think it would be much more helpful if DroneDeploy could give estimated relative measurement accuracy numbers based on the GSD, sidelap/overlap, how many angles, and if GCPs were used. I’m sure you could come up with a formula to take all those things into account and give estimated numbers.
I’ve seen lots of posts on here from people that verified volume calcs via other methods (laser scanner or having already known volumes) and found the numbers to more off than 2-5% like you see posted in many blogs posts as to the accuracy to expect. Obviously the GSD and whether you also took obliques has a significant impact.
It is widely published that relative horizontal distance accuracy will be 2X GSD and veritcal 3X. I think that’s just a map created only with nadirs, min 65% sidelap and 75% frontlap. However with the obervations about volumetric calcs being off more than expected I’m wondering how accurate those 2X and 3X GSD assumptions really are. I did a football field one time at 0.8in/pix, laid out GCPs and took a 300ft roll tape measure to verify the distance and the length of the football field measured in the resulting map was off by 5 inches, when using the 2X GSD, it should have not been more than 1.6 inches. There’s not that much curvature of the earth in 300 feet. Maybe one could argue the field wasn’t perfectly flat, so let’s give it 3 inches. Still the actual was almost twice.
So for my own estimates I use 4X GSD for horizontal and 6X GSD for veritical relative accuracy estimates. Anyone else doing something similar based on their own observations?