A total station is an optical instrument used in modern surveying and arhaeology as well as by police , crime scene investigators, private accident reconstructionists and insurance companies to take measurements of scenes . It is a combinatoon of an eletronic theodolite (transit ), an electronic distance meter (EDM) and software running on an external computer known as a data collector.

With  a total station one may determine angles and distances from the instrument to points to be surveyed. With the aid of trigonometry and triangulation , the angles and distances may be used to calculate the coordinates of actual positions (X,Y and Z  or northing , easting and elevation ) of surveyed points , or the position of the instruments from known points , in absolute terms.

Measurement of distance is accomplished with a modulated microwave or infared carrier signal , generated by a small solid - state emitter within the instrument's optical path , and bounced off of the object to be measured . The modulation  pattern in the returning signal is read and interpreted by the onboard computer in the total station . The distance is determined by emitted  and receiving multiple frequencies , and determining the integer number of wavelengths to the target for each frequency . Most total stations use a purpose - built glass Porro prism as the reflector for the EDM signal , and can measure distances out to a few kilometers , but some instruments are " reflectorless" , and can measure distances to any object that is reasonably light in color , out to a few hundred meters . The typical TotalStation EDM can measure distances accurate to about 3 millimeters or 1/100th of a foot.