Explain the principles of photogrammetry in mapping.

Photogrammetry extracts measurements and 3D information from photographs. Aerial photogrammetry uses overlapping photographs (60% forward, 30% side overlap) from aircraft or drones. Stereo pairs viewed in stereo-plotter enable 3D measurement. Ground control points with known coordinates orient photographs. Bundle adjustment refines camera orientation parameters. Products include orthophotos (geometrically corrected images), DEMs, contour maps, and 3D models. Modern digital photogrammetry uses automated image matching. UAV photogrammetry increasingly used for site surveys and progress monitoring.