tacheometry

thumb|Diagram of measurements: D is the slant distance; S is the horizontal distance; Δh is the vertical distance.

Tacheometry (; from Greek for "quick measure") is a system of rapid surveying, by which the horizontal and vertical positions of points on the Earth's surface relative to one another are determined using a tacheometer (a form of theodolite). It is used without a chain or tape for distance measurement and without a separate levelling instrument for relative height measurements.