How can I properly place checkpoints and ground control points?

Question

How can I properly place checkpoints and ground control points?

Answer/Cause

Recommended Locations for Check Point and Ground Control Point Placement

Flat, Level Areas

Reason: Ensures consistent elevation around the control point, leading to accurate measurements.

Areas Free of Surface Irregularities Around the Control Point

Reason: This helps reduce variability in the 3D data generated by SfM, stabilizing the nearby points and enabling more accurate comparisons with the measured values. As a result, more reliable validation becomes possible. Before placement, please make sure the ground around the checkpoints is level.

Soft Ground

Reason: On muddy or soft ground — for example, after rain or on volcanic ash — the survey pole can sink into the surface, causing a discrepancy between the actual ground surface and the recorded control point position.

Locations to Avoid for Checkpoint and Ground Control Point Placement

Areas with Slopes or Uneven Surfaces

Reason: Slopes cause inconsistencies in elevation around the control point, making accurate surveying difficult.

Soft Ground

Reason: On muddy or soft ground — for example, after rain or on volcanic ash — the survey pole can sink into the surface, causing a discrepancy between the actual ground surface and the recorded control point position.

Areas with Overgrown Vegetation

Reason: In drone photogrammetry, point clouds are generated from the surfaces visible in the photos. In overgrown areas, the point cloud captures the top of the vegetation rather than the ground itself, which can introduce errors of several centimeters. Whenever possible, place checkpoints on bare, exposed ground.

Areas with Overhead Obstacles (e.g., Trees)

Reason: Overhead obstacles such as tree branches can block the drone's line of sight to the ground and interfere with GNSS satellite signal reception, reducing accuracy. Whenever possible, place checkpoints in areas free of overhead obstructions.