so anyway i finally got hired to do an actual paid survey job for a small land developer, just a residential plot about 6 acres, nothing crazy. flew it with 80/75 overlap, had the mavic 3E, used DroneDeploy for the flight plan and processing.

the orthomosaic looked great to me, colors were good, resolution seemed fine. sent it to the client and they came back saying it doesnt match their existing CAD drawings and theres like a 2-3 meter offset in places. i didnt use any GCPs because i thought the RTK on the drone would handle it. client is not happy and now im second guessing everything.

is RTK actually not enough for survey-grade output? i thought that was the whole point of paying for the 3E. did i miss something obvious here

RTK alone can get you pretty close but 2-3m offset sounds like maybe you had a bad fix during the flight or the base corrections werent coming through properly. what base were you using, network RTK through a service or your own base station? ive seen network RTK give garbage results in areas with poor CORS coverage and the drone just silently logs the positions anyway without flagging it as unreliable.

also worth checking whether the CAD drawings themselves are in the right coordinate system, sometimes the clients reference files are older and in a local or assumed datum and they expect you to figure that out. not saying thats what happened here but ive had that exact argument with a surveyor before.

yeah RTK is not a substitute for GCPs if the client needs survey-grade accuracy, or at minimum you should have checkpoints to verify. the 3E is a good machine but even Mavic marketing doesnt claim centimeter accuracy without a proper base setup and validation. honestly for anything going to a developer or engineer i always put down at least 4-5 GCPs no matter what the drone supposedly supports, takes maybe 20 extra minutes and saves you exactly this conversation later