= Solution
Use \b[low-altitude <structure-from-motion photogrammetry>], with strongly overlapping aerial images and well-distributed surveyed <ground control points>. Bundle adjustment estimates camera geometry and a dense surface reconstruction; independent check points test its accuracy. A small unmanned aircraft or carefully controlled close-range aerial platform can cover the $0.05\,\mathrm{km^2}$ site with centimetre ground sampling. Surveyed targets and stable camera calibration are essential: centimetre pixels alone do not establish centimetre vertical accuracy.
For exposed trench walls or especially demanding local geometry, terrestrial <lidar> is an alternative or complement. Remove vegetation where permissible, retain the trench’s sharp topographic breaks and state whether the output is a visible surface model or a bare-ground <digital elevation model>.
Back to article page
