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Use 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 $0.05\mathrm{k}{\mathrm{m}}^2$ 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.

Three-dimensional reconstruction using two or more overlapping photographs from different viewing positions. Corresponding image points define viewing directions whose intersection estimates the surface position. Surveyed camera positions and orientations, camera calibration and ground control points establish the coordinate geometry. Ordinary optical stereo models the visible surface, which can be forest canopy rather than bare ground.

A photogrammetry workflow jointly estimating camera geometry and scene structure from many overlapping images, commonly followed by dense surface reconstruction. Ground control points or accurately surveyed camera positions establish scale and georeferencing. Independent check points test accuracy rather than participating in the fit. A fine image ground-sampling interval does not alone establish equal vertical accuracy.