Angles and distances are measured from the total station to points under survey, and the coordinates (X, Y, and Z or easting, northing, and elevation) of surveyed points relative to the total station position are calculated using trigonometry and triangulation. The coordinates of an unknown point relative to a known coordinate can be determined using the total station as long as a direct line of sight can be established between the two points.
Reflectorless total stations can measure distances to any object that is reasonably light in color, up to a few hundred meters. A typical total station can measure distances up to 1,500 meters (4,900 ft) with an accuracy of about 1.5 millimeters (0.059 in) ± 2 parts per million.
Most total stations use purpose-built glass prism (surveying) reflectors for the EDM signal. The distance is determined by emitting and receiving multiple frequencies, and determining the integer number of wavelengths to the target for each frequency. The modulation pattern in the returning signal is read and interpreted by the computer in the total station. Measurement of distance is accomplished with a modulated infrared carrier signal, generated by a small solid-state emitter within the instrument's optical path, and reflected by a prism reflector or the object under survey.
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