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Total station

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A total station is a highly precise electronic and optical instrument used for surveying and building construction. It functions as an electronic transit theodolite integrated with electronic distance measurement, often called EDM. This combination allows the device to measure both vertical and horizontal angles, as well as the slope distance to a specific point. An on-board computer is included to collect this data and perform complex mathematical calculations. These calculations include triangulation, position resection, and intersection to determine exact locations.

Prism Target used with survey equipment
Prism Target used with survey equipment

By combining these tools, a total station provides a complete picture of the physical space around it.

The mechanism for measuring angles involves electro-optical scanning. Inside the instrument, there are rotating glass cylinders or discs etched with extremely precise digital bar-codes. The instrument scans these codes to determine the angle. High-quality total stations can achieve a standard deviation of 0.5 arc-seconds. In contrast, cheaper "construction grade" models usually have a standard deviation of 5 or 10 arc-seconds. To ensure accuracy, operators often perform a "set collection." This involves sighting a target in both "direct" and "reverse" modes, where the scope is flipped or "plunged" 180 degrees. The resulting angles are then averaged to create a mean angle.

Prism Target used with survey equipment
Prism Target used with survey equipment

Distance measurement relies on a modulated infrared carrier signal. A small solid-state emitter within the instrument's optical path sends this signal toward a target. This target is typically a purpose-built glass prism reflector. The signal reflects off the prism and returns to the instrument. The on-board computer interprets the modulation pattern of the returning signal. It determines the distance by emitting multiple frequencies and counting the integer number of wavelengths required to reach the target. Most total stations can measure distances with an accuracy of about ± 2 parts per million. Some models are "reflectorless," meaning they can measure distances to any reasonably light-colored object up to a few hundred meters away.

To determine coordinates, the total station uses trigonometry. It measures angles and distances from its own position to points under survey. This allows it to calculate X, Y, and Z coordinates, which represent easting, northing, and elevation. To find an absolute location, the instrument must have a line of sight to known points. This can be done by setting the device over a known point or through "free stationing," which uses two or more points with known locations. Some modern models include a Global Navigation Satellite System (GNSS) receiver. This allows the device to determine coordinates without needing a direct line of sight to other points, though GNSS can have lower accuracy in the vertical axis.

GPS-mätning på järnåldersboplats i Ytterby sn, Bohuslän, den 28 april 2006. Bild 1
GPS-mätning på järnåldersboplats i Ytterby sn, Bohuslän, den 28 april 2006. Bild 1

These instruments are vital across many professional fields. Archaeologists use them to record artifact locations and site topography with millimeter accuracy. In the mining industry, the total station is the primary tool for surveying. Miners use it to record the locations of tunnel walls, floors, and ceilings, known as "backs." They install small steel plugs in the walls or backs to act as control stations. This data is then downloaded into Computer-Aided Design (CAD) programs to ensure the mine follows its designed layout.

In construction, total stations are the highest standard for layout tasks. They are frequently used to locate penetrations for underground utilities, foundations, and roofing. Many modern jobs use Building Information Modeling (BIM), where coordinates for pipes and ducts are available digitally. The total station helps translate these virtual models into tangible structures. Meteorologists also use this technology to track weather balloons. By measuring the change in azimuth and elevation as a balloon rises, they can compute wind speed and direction at different altitudes. They also track ceiling balloons to find the height of cloud layers for aviation forecasting.

GPS-mätning på järnåldersboplats i Ytterby sn, Bohuslän, den 28 april 2006. Bild 1
GPS-mätning på järnåldersboplats i Ytterby sn, Bohuslän, den 28 april 2006. Bild 1

The evolution of these tools has been driven by many specialized manufacturers. Historical makers include Carl Zeiss, Hewlett-Packard, and Wild Heerbrugg AG. Today, major industry players include Leica Geosystems and Sokkia, both of which are part of Hexagon AB. Other notable companies include Nikon, which is part of the Trimble North Group LTD, and Topcon. Some models are even robotic or motorized. These allow an operator to control the instrument via remote control from a distance. While this can eliminate the need for an assistant, many surveyors still use one to prevent people from disrupting the tripod or to guard against the theft of the valuable equipment.

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File:Prism Target used with survey equipment.jpg
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