Recently I did a construction site. Shot it a 1in/pixel GSD with a Phantom 4 Pro. Frontlap 75%, Sidelap 75%. I gave the orthophoto (GeoTIFF) to the Land Suveying company that surveyed the property and the photo wouldn’t line-up right when they brought it into Carlson Survey. It was fairly close but a lot of the building edges in the photo were quite a bit off from the survey drawing, a few feet off.
My understanding that is that relative accuracy should be 2-3 times the GSD. So if I shot at 1in/pixel, then things should line-up within 3 inches, no?
We didn’t use ground control points because this was actually an inspection job for the lender to view the status of the project and the Surveying Company that was working with the lender neglected to tell us upfront they wanted to overlay it on an existing survey map. However I’m trying to figure out what the cause of the inaccuracy would be as I would think 75/75 overlap and 1in/pixel GSD should produce pretty good relative measurement accuracy. Yes, the geolocation coordinates in the GeoTiff would be off since we had not ground control points, but I would think you should be able to manually align it.
We were joking that maybe the builder didn’t build the buildings correctly! But we are assuming they did. The site was only about 5 acres.