Total Station in Surveying: How It Works on a Building Site

A total station is the surveying instrument that measures horizontal angles, vertical angles and distances in one unit, and computes the coordinates of the points it observes. It combines an electronic theodolite with an electronic distance meter and an onboard computer. On a construction site it is the tool that turns a drawing into physical positions: grid lines, column centres, bolt groups and façade brackets are set out with it, and the finished structure is checked against design with it.

This article explains what the instrument measures and how, the main types, how it is used through the life of a project, the sources of error, and the framework of survey control and registered surveyors in Singapore.

What a total station measures

The instrument sits on a tripod over a known point and is levelled precisely. It then measures three things to a target: the horizontal angle from a reference direction, the vertical (zenith) angle, and the slope distance. From these it calculates the horizontal distance and height difference and, if the station’s coordinates and orientation are known, the coordinates of the target.

Angles are read by glass circles with fine coded graduations, read electronically by sensors; angular precision is quoted in seconds of arc. Distances are measured by an electronic distance meter (EDM) that sends a modulated infrared or laser beam to the target and analyses the returned signal, either by phase comparison or by timing pulses. Distance precision is usually quoted as a fixed part in millimetres plus a part proportional to distance. Temperature and pressure affect the speed of light in air, so the instrument applies an atmospheric correction.

Types of total station

Manual or conventional instruments are aimed by the surveyor through the telescope and need a prism held at the target.
Reflectorless instruments can measure to a surface without a prism, which is useful for measuring façades, soffits and inaccessible points, though accuracy and range are generally lower than to a prism.
Robotic instruments have motorised drives and automatic target recognition. They track a prism held by a single operator, who controls the instrument from a handheld controller at the target. They are widely used for setting out and for automated monitoring.
Imaging and scanning total stations add cameras or scanning capability, bridging towards laser scanning.

The instrument evolved from the theodolite, and the angular principles are the same. Our article on the theodolite explains that lineage.

How a total station is used on a construction site

On a building project the instrument is used at almost every stage:

Control: establishing and checking a network of reference points around and within the site, tied to the national coordinate system.
Setting out: marking the building grid, pile positions, retaining-wall lines, column and wall positions, and anchor bolts. Design coordinates are loaded into the instrument, which then guides the surveyor to each point.
Checking: verifying formwork and steelwork before concreting or bolting, and checking verticality of columns and cores as the building rises.
As-built survey: recording what was actually built for comparison with design and for the record.
Monitoring: measuring prisms fixed to retaining walls, neighbouring buildings or the structure itself to detect movement during excavation and construction.

Pile positions are a good example of why this matters. A pile installed off position introduces eccentricity into the pile cap, which the engineer may need to check and redesign. Accurate setting out at the start avoids that. See bored piles for the pile-side view, and construction surveying for the broader workflow.

Accuracy and the sources of error

A total station is only as good as its set-up and the control it is tied to. Common sources of error include poor centring and levelling over the station point, disturbed or misidentified control points, incorrect prism constants, wrong atmospheric settings, instrument collimation errors, and simple blunders such as a wrong coordinate typed in. Good practice relies on redundancy: observing in both faces of the telescope to cancel instrument errors, closing traverses, checking against independent control and resecting from several known points.

Heat shimmer, vibration from nearby plant and long sight lines in direct sun all degrade results. On tall buildings, building movement under sun and wind is itself measurable, which is why vertical control on high-rise cores is often transferred at stable times of day and checked by independent methods.

Survey control and registered surveyors in Singapore

Singapore’s survey framework is maintained by the Singapore Land Authority (SLA). The national horizontal coordinate system is SVY21 and heights are referred to the Singapore Height Datum (SHD). SLA also operates SiReNT, the Singapore Satellite Positioning Reference Network, which provides a national reference frame for satellite positioning. Site control networks are tied to these so that the building sits correctly within its land lot and relates to roads, drains and neighbouring developments.

The Land Surveyors Board registers land surveyors under the Land Surveyors Act and issues practising certificates. Cadastral surveys, those that define legal boundaries, must be carried out by registered surveyors with a valid practising certificate under the requirements of the Chief Surveyor. On building projects, the positioning of a building relative to its boundaries and the associated survey plans therefore involve a registered surveyor, while day-to-day setting out may be carried out by the contractor’s site surveyors working from that control. The exact certification required at each stage depends on the project and authority requirements, and should be confirmed with the Qualified Person.

Survey work also interacts with other professions on site: the engineer relies on it for pile and structure positions, and the quantity surveyor may rely on measured quantities, though that profession deals in cost rather than position.

Frequently asked questions

What is the difference between a total station and a theodolite?

A theodolite measures horizontal and vertical angles only. A total station adds an electronic distance meter and a computer, so it measures distances too and calculates coordinates directly. Modern total stations have largely replaced theodolites on construction sites.

Can a total station measure without a prism?

Reflectorless instruments can measure directly to surfaces such as concrete or brick, which is useful for inaccessible points. Accuracy and range are typically better when measuring to a prism, so prisms are still used for precise setting out and monitoring.

What is a robotic total station?

A robotic total station has motorised drives and automatic target tracking, so one surveyor can operate it remotely from the prism position. It is efficient for setting out and is used for automated, continuous monitoring of structures and excavations.

Who can carry out a boundary survey in Singapore?

Cadastral surveys that define legal boundaries must be carried out by a registered surveyor holding a valid practising certificate from the Land Surveyors Board, following the Chief Surveyor’s requirements at the Singapore Land Authority.

Need pile positions, setting-out deviations or monitoring results reviewed by a structural engineer? Talk to our consultancy or get in touch.