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Total Station

Total stations are basically integrated combinations of electronic theodolite & distance measurer. All modern versions have large on-board memories & some (e.g. Nikon) have a display that shows points in map form. They come in three types, standard, reflectorless & robotic. A standard instrument is used by two people, one sighting through & controlling the total station & the other holding a staff carrying a prism (reflector). This is held on or over the point to be measured & a modulated red laser is fired at it from the total station. The time taken for the beam to return to the total station is directly proportional to the separation of the instrument & the reflector. At the same time the total station measures the horizontal & vertical angle & therefore the exact position of the prism can be calculated.

Reflectorless types are used primarily to record standing structures where holding a prism would be impractical. Sometimes small targets are stuck to the structures but some can be used without targets. The final (& most expensive) type is the robotic which is designed for one person use. The prism is carried by the surveyor who communicates with the unattended total station via a radio link.

Total stations have a key advantage over GPS in that they are unaffected by trees & can be used inside buildings. For most detailed mapping projects a combination of both technologies is used, especially in rural areas.

Incidently, the 3D laser scanners that have become popular in recent times are essentially nothing more than automated reflectorless total stations.

Manufacturers

Nikon-Trimble
Topcon

Web sites

http://www.nikon-trimble.com
http://www.topcon.co.uk