Ground control and RTK for accuracy

Photogrammetry reconstructs the shape of a site very well on its own. What positions that shape correctly in the real world — the absolute accuracy — is your control.

RTK / PPK

A drone with RTK (or post-processed PPK) tags each photo with a centimetre-level position. For most mapping work this alone gives strong, repeatable accuracy with no ground work. Whether it meets a given specification is a question your checkpoints answer, not the drone.

Ground control points (GCPs)

GCPs are marked, surveyed points on the ground. They anchor the model to a known datum and let you verify accuracy independently. Use them when a deliverable will be relied on for design, legal, or as-built purposes.

Hand yours over as a gcp_list.txt on the Control step of a raw-photo project. It is not a file you mix in with the imagery: put it in with the photos and it is left out without an error, and the map is positioned by the drone's GPS alone.

Checkpoints

Surveyed points you don't use in processing are checkpoints — they measure how accurate the result actually is. DroneFlow's checkpoint tool reports the residuals so you can prove the number, not just claim it.