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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.

Recovery of object positions and shape from photographs with overlapping views. Known or estimated camera geometry and matched image features constrain three-dimensional point positions. A metric reconstruction requires scale and a coordinate reference; image pixel size is not automatically the positional accuracy of the reconstructed surface. Stereo photogrammetry and structure-from-motion photogrammetry use related geometry with different acquisition and camera-estimation strategies.