Among the newest computer-driven technologies available to assist surveying engineers in their work of developing and processing spatial data are (1) total station instruments, including robotic systems; (2) the global positioning systems (GPS); (3) digital photogrammetry and light detection ranging (LIDAR); (4) satellite remote sensing; and (5) geographic information system (GIS).
These new systems are enabling surveying engineers to provide new and better types of information at lower cost and in fraction of time previously required.
A total station is an optical instrument used in modern surveying and archaeology as well as by police, crime scene investigators, private accident reconstructionists and insurance companies to take measurements of scenes. It is a combination of an electronic theodolite (transit), an electronic distance meter (EDM) and software running on an external computer known as a data collector.
They can also measure angles both in horizontal planes and vertical planes, and again the results can be automatically displayed and stored.
The on-board computer can use these measured data in real time to resolve horizontal and vertical distances, to calculate the positions and elevations of points, or to set points for construction projects.
Total station instruments are probably the most commonly used and important instruments in modern surveying today, having practically replaced all transits, theodolites, and stand alone EDM instruments.
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 instrument from known points, in absolute terms.
The data may be downloaded from the theodolite to an external computer and application software will generate a map of the surveyed area.
Field to Finish Operation Control/operation (robotic) Measurement and basic comps Final Comps, checks and outputs Transfer remotely (radio/cell phone) Memory card USB and Compact Flash Automatic target recognition
Some total stations also have a GPS interface which combines these two technologies to make use of the advantages of both (GPS - line of sight not required between measured points; Traditional Total Station - high precision measurement especially in the vertical axis compared with GPS) and reduce the consequences of each technology's disadvantages (GPS - poor accuracy in the vertical axis and lower accuracy without long occupation periods; Total Station - requires line of sight observations and must be set up over a known point or within line of sight of 2 or more known points).
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 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 emitting 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 Total Station EDM can measure distances accurate to about 3 millimeters or 1/1000th of a foot.
Total stations are used by police, crime scene investigators, private accident reconstructionists and insurance companies to take measurements of scenes. Once they take accurate measurements with a total station they can use software to recreate the accident in a 3D animation .
Total stations are the primary survey instrument used in many mining applications.
As the development drifts in an underground mine are driven, a total station will be used to record the absolute location of the tunnel walls ( stope ), ceilings (backs), and floors. This data can then be loaded into a CAD program, and compared to the designed layout of the tunnel.
At regular intervals, the survey party will install stations. These are small steel plugs that are drilled into the walls or the back. The plugs are installed in pairs. For wall stations, two plugs are installed in opposite walls, forming a line perpendicular to the drift. For back stations, two plugs are installed in the back, forming a line parallel to the drift.
When the survey crew wants to set up the total station in a drift, they use a set of plugs to locate the total station.
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