How many ground control points does a drone survey need?
No standard sets a number. ASPRS Edition 2 asks for ground control that is well spread over the site, with more points on larger sites (Addendum V, A.7.1).
Research on drone mapping blocks recommends GCPs round the edge plus an even spread inside (Martínez-Carricondo et al., 2018). The planner does this at a spacing you choose, 150 m by default, which is a practical default and not an ASPRS rule.
What ASPRS Edition 2 says
ASPRS Edition 2 does not set a number of GCPs for drone surveys. Addendum V (A.7.1) notes that no research yet supports a fixed rule for how many to use or where to put them. It asks for control that is well spread across the site, with more points on larger sites. Where a sensor maker recommends a number, it advises checking that research backs it up.
Reference
Martínez-Carricondo, P. et al. (2018) “Assessment of UAV-photogrammetric mapping accuracy based on variation of ground control points,” International journal of applied earth observation and geoinformation, 72, pp. 1–10. Available at: https://doi.org/10.1016/j.jag.2018.05.015.
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