The total station is the essential tool of a land surveyor. So essential, that it is often referred to as a "gun" by our land surveying cousins over the pond. It typically comprises of an electronic transit theodolite and an electronic distance meter (EDM).
The theodolite measures horizontal and vertical angles, relative to the set up angle. The EDM uses a "time of flight" laser to measure distances to targets. Resulting coordinates are typically saved digitally.
What is it used for?
Most total stations come with pre-installed software/apps and options to install more. Combined with the core features - a wide variety of surveying tasks are possible in the right hands. Conventional land surveying techniques are faster and more accurate than ever before.
Before total stations, surveyors needed assistants to help to operate manual instruments. They used theodolites, transits and levels. Distances were measured with metal chains or tapes and software was a notepad and pencil.
Specifications of a modern total station vary according to manufacturer and model. Survey grade models come with the ability to lock to and track a target (glass prism). This allows the surveyor to operate independently where safe to do so.
Another popular feature is Reflectorless EDM. This removes the need for a prism to reflect the laser back to the instrument. It's particularly useful for measuring features at height, such as overhead power lines, to measure ground levels on adjacent land, where access is not granted, or to measure road markings on a busy road without putting the surveyor in harm’s way.
Does it have limitations?
The main limitations of using a total station to conduct a topographic survey are line of site and range. It cannot measure what the laser cannot reach. Total stations are frequently paired with GPS methods. The surveyor can roam freely and take measurements with the GPS unit which tracks satellites to determine current coordinates.
The data from the total station, or it's remote controller, is output as lines and points. These are usually combined with data from other tools used on site and processed to produce 2d CAD line drawings and 3d Digital Terrain Models. Only the points and lines required to meet the survey specification are measured. Most end users are still using these styles of drawing to inform their decision making.
What about speed?
Laser scanners and drones are transforming the way data is collected by surveyors. Up to millions of points are measured in a fraction of the time taken with a total station. A cloud of points is produced from which dense, data rich deliverables can be provided. Alternatively, points and lines can be extracted from the cloud to produce a more traditional drawing.
The processing of the point cloud can be time consuming, especially where standard CAD drawings are the goal. Points are not independently selected to be measured by the surveyor. Instead, a "scatter" method produces millions of points across the area.
Final thoughts…
The total station is still the tool of choice to control the accuracy of the data produced by Laser Scanners and Drones. It is likely to feature in a survey project, even if not used as the main data collection tool. Essentially, a wide range of tools allows the surveyor to pick those which complement each other for the task in hand. We expect the total station to be an essential part of that toolkit for many years to come.
Image credits:
(Left) Leica TS16 - https://leica-geosystems.com
(Right) Trimble S9 - http://www.trimble.com/
Other models/manufacturers are available.
