Are you using GCP’s? If not you can expect up to a 3m (10ft) shift including in between different flights. It’s all dependent on the environment and the quality of the satellites.
No, I am not using GCPs. This is beyond my equipment and capabilities.
My project is to create a DD map, then overlay GPS waypoints (from a phone app) together in Google Earth. The location is filled with vehicles that move often, so we cannot use old Google Earth maps.
The focus of the study is to determine how accurate the phone app GPS waypoints are, compared to known objects captured by the drone map. We capture the GPS waypoints in front of the vehicles at a measured distance from that vehicle.
Without knowing the precise coordinates for the known objects, it will be difficult to quantify how precise the phone’s gps (through the app) actually is. And, your DD map created from the drone isn’t going to be much help I’m sorry to say. You are trying to compare 2 points to each other where each of them could be off by meters. If this research is important, you need to determine reliable coordinates for objects that you want to use to check the phone app against.
You need to fly it and create rough GCP’s off of that map. This will at least get the horizontal aligned. You can run an auto level on those after the fact if you want to increase vertical accuracy.