ok so background: i do mostly real estate and some inspections, never really done proper mapping with ground control before. got asked to do a topographic survey for a small land parcel, maybe 8 acres, client needs it for a drainage study. i figured this was a good excuse to finally learn how to do it right so i borrowed a friends RTK GPS to mark out 6 GCPs, laid out the targets (printed the 18x18 inch ones i found in a thread somewhere on here), flew a double grid at like 85m AGL with 80/75 overlap.

processed in DroneDeploy and imported my GCP coordinates but the reprojection errors are showing like 4-8cm on some of them which i thought was supposed to be under 2cm or something. im not sure if i screwed up how i measured the GCPs, or if it's a coordinate system mismatch, or if my overlap wasnt enough, or honestly i dont even know. the map looks visually fine but obviously that doesnt mean the accuracy is actually there. any idea where to even start debugging this

coordinate system mismatch is almost always the first thing to check, its the thing that trips up everyone the first time. what datum and projection did you record your GCPs in, and what did you set the project to in DD? if youre in the US and your RTK was outputting in WGS84 lat/lon but your project is set to a state plane or vice versa things will look wildly off. also - when you say you borrowed a friends RTK GPS, how confident are you that it was actually getting a fixed solution when you were logging those points? a float solution can be off by several centimeters which would explain some of your scatter.

the overlap sounds fine so id rule that out first and focus on the GCP collection side of things

yeah the coordinate thing is probably it, been there. also 4-8cm reprojection error isnt catastrophic depending on what the client actually needs for the drainage study - like a licensed surveyor is going to need sub-2cm but if its just for rough grading and drainage planning that might actually be acceptable, worth asking before you spiral too hard on it. that said definitely figure out why before you submit anything