|Total Station Laser :
Total Station Laser
A total station is an electronic/optical instrument used in
modern surveying. The total station is an
electronic theodolite (transit) integrated with an
electronic distance meter (EDM) to read slope distances from the
instrument to a particular point.
Robotic total stations allow the operator to control the instrument
from a distance via remote control. This eliminates the need for an
assistant staff member as the operator holds the reflector and controls
the total station from the observed point.
Coordinate measurementCoordinates 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. Angles
and distances are measured from the total station to points under
survey, and the coordinates (X, Y, and Z or northing, easting
and elevation) of surveyed points relative to the total station position
are calculated using trigonometry and triangulation. To determine an
absolute location a Total Station requires line of sight observations
and must be set up over a known point or with line of sight to 2 or more
points with known location.
Most modern total station instruments measure angles by means of
electro-optical scanning of extremely precise digital bar-codes etched
on rotating glass cylinders or discs within the instrument. The best
quality total stations are capable of measuring angles to 0.5
arc-second. Inexpensive “construction grade” total stations can
generally measure angles to 5 or 10 arc-seconds.
Measurement of distance is accomplished with a
modulated microwave or 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. The modulation pattern
in the returning signal is read and interpreted by the computer in the
total station. The distance is determined by emitting and receiving
multiple frequencies, and determining the integer number
of wavelengths to the target for each frequency. Most total stations use
purpose-built glass corner cube prism reflectors for the EDM signal. A
typical total station can measure distances with an accuracy of about
1.5 millimetres (0.0049 ft) + 2 parts per million over a distance of up
to 1,500 metres (4,900 ft).
Reflectorless total stations can measure distances to any object that is reasonably light in color, to a few hundred meters.
Some models include internal electronic data storage to record
distance, horizontal angle, and vertical angle measured, while other
models are equipped to write these measurements to an external data
collector, such as a hand-held computer.