What Is a Total Station and How Do Surveyors Use It?

A total station is a precision surveying instrument that measures three things in one unit: horizontal angles, zenith angles and slope distances.

Caltrans' Surveys Manual describes exactly that instrument — one that may carry onboard software, connect to an external data collector, or do both.

The design is the point: the angle measurements and the distance measurement come out of one instrument.

Caltrans' manual calls the distance-measuring electronics the EDM — electronic distance measuring — circuitry, and the computing side, onboard software or an external data collector, holds the measurements and runs the field math on them.

That field math is a real part of the job.

Caltrans notes that data collection software can perform coordinate geometry (COGO) computations, and that stakeout computations are generated in the data collector and sent to the total station or a GNSS receiver.

The instrument and its collector work as one system in the field.

It is also delicate electronics.

Caltrans warns crews never to point the telescope directly at the sun, because the sun's rays can damage the EDM circuitry, and to shade the instrument because heat can reduce the EDM's range.

The measuring optics and the EDM electronics live in one instrument, so instrument care and measurement quality are the same job.

What the instrument measures is two angles and one distance.

It reads the horizontal angle between two directions, the zenith angle, and the slope distance along the line of sight — the three quantities Caltrans' manual names as a total station's work.

The distance comes from the EDM, which determines the slope distance to the prism or surface electronically.

That is also why the EDM sits at the center of the instrument's care rules, from the sun warning to heat shading.

The data side does the math.

Caltrans notes that data collection software can perform coordinate geometry computations, so raw angles and distances become coordinates while the crew is still in the field.

Stakeout runs the other direction: the collector generates the stakeout computations and sends them to the total station or a GNSS receiver.

The instrument polices itself, too.

Caltrans notes that most total stations are equipped to detect and correct various instrumental errors, and that error codes display when errors exceed the program's limits.

Self-correction covers the predictable instrument errors; it does not replace an agency's or a firm's own check schedule — Caltrans, for one, tells crews to calibrate or collimate total stations daily and to service them approximately once every eighteen months.

There is an external yardstick for distance measurement as well.

NGS has established more than 400 EDMI Calibration Base Lines across the United States so surveyors can detect and correct errors in electronic distance measuring instruments, and its CALIBRATE program computes the scale and constant corrections.

The parts map to the three jobs — angles, distances, data — plus the base everything rides on:

• The telescope and the angle sensors. The optics the operator aims, and the sensors that read the horizontal and zenith angles.
• The EDM. The distance-measuring electronics. The sun and heat warnings exist to protect this circuitry.
• Onboard software or an external data collector. Holds the measurements and runs the COGO and stakeout computations. In one maker's 2020 chart, its automated models add a remote-control link to a field controller.
• The tribrach and its levels. The base that carries the instrument over the point. Caltrans tells crews to check a tribrach's bullseye level and the vertical collimation of its plummet routinely.
• Motor drives, on some models. In one maker's 2020 comparison chart, the manual models show no motorisation, while the automated models list motor drives, automatic target aiming and remote control.

The last part lives off the instrument: the prism at the target end.

Caltrans lists standard prisms, mini prisms, 360-degree prisms and active prisms, and cautions that each prism will likely have a different offset value, so the instrument must be set to the correct value for the prism in use.

Caltrans adds the classic blunder rule: when the total station is run from an external data collector, the prism constant should be set in either the total station or the data collector — never in both.

The types split on two questions: does the instrument turn itself, and does the measurement need a prism?

Manual vs robotic.

A manual instrument is aimed and turned by the operator for every measurement.

In one manufacturer's 2020 comparison chart, the manual models show no motorisation, while the automated models add motor drives, automatic target aiming and remote control from a field controller.

The automatic aiming has a documented mechanism, at least for one maker.

Its technical data explains automatic target recognition (ATR).

The instrument sends an invisible laser beam that any standard prism reflects; a camera measures the offset of the returned spot, and the motors drive the crosshairs onto the prism.

Small remaining offsets are applied mathematically to the angles.

Reflectorless.

Reflectorless EDM drops the prism entirely: the instrument measures to a surface — pavement, in Caltrans' reflectorless breakline surveys.

Ranges are model ratings, not industry numbers: one maker rates its reflectorless EDM as R500, R1000 or R2000 — above 500 m, above 1,000 m or above 2,000 m — with the rating measured to a Kodak gray card that is 90% reflective.

Real surfaces that are darker or angled return less.

Accuracy falls off without the prism as well.

In the same chart, reflectorless distance accuracy is 2 mm + 2 ppm up to 500 m and 4 mm + 2 ppm beyond, against 1.0 mm + 1.5 ppm to a prism on most models.

Caltrans' survey methods add the field-side caveats for reflectorless work on pavement.

The instrument generally needs to be set up high enough to aim down on the surface.

Maximum sight distances run shorter than conventional prism surveys, set-ups that are not high enough give less accurate laser measurements, and Caltrans advises checking laser measurements against measurements to a prism.

The aim angle matters too: a laser measurement perpendicular to a surface is more accurate than one at a large angle of incidence, because the beam elongates and produces distance errors.

The instrument's measurements sit underneath a lot of crew work:

• Traverse and control work. The angles and distances measured between stations are what traverse closure and adjustment calculations run on — calculations O*NET lists among surveying technicians' tasks.
• Topographic measurement. Ground points, breaklines and features, shot by shot — or by reflectorless laser, as in Caltrans' reflectorless pavement breakline surveys.
• Construction staking and layout. The collector computes the stakeout points and sends them to the instrument, and setting out stakes, marks and monumentation is among O*NET's top tasks for surveying technicians.
• Feature and position collection. COGO in the data collector turns sighted points into coordinates the office can draft from.

BLS describes the same tool set from the outside.

It says surveyors use handheld GPS units and robotic total stations in the field, then GIS to present spatial data and CAD software to create digital maps — and it lists CAD work among technicians' data-processing duties.

Those measurements still take two positions on the ground: someone operating the instrument, and someone holding the rod or target the operator sights on — the same two tasks O*NET describes.

The instrument sits at the center of the crew's division of labor:

• The instrument operator runs it. O*NET lists adjusting and operating surveying instruments — prisms, theodolites, electronic distance measuring equipment, electronic data collectors — among the occupation's core tasks, which is this seat's work.
• The rod person positions and holds the vertical rod or target the operator sights on to measure angles, distances and elevations — O*NET describes that as a core task too. The pole's bubble matters here: Caltrans warns that a maladjusted bubble on a prism or rover pole can cause systematic error, and tells crews to check the pole clamp and length before and after use.
• The party chief is the crew's supervisor in one historic federal ruling — DOL's Davis-Bacon AAM 16 treated the party chief as a bona fide supervisor, while it treated chainmen, rodmen and instrument men as laborers or mechanics.
• The survey technician — O*NET's reported job titles for the occupation include Rodman and Survey Technician, and BLS says technicians may clear brush from the survey line or use drones to take photos alongside the instrument work.

The survey technician career guide covers the role end to end, and crew openings post as survey technician jobs on the board.

Crews use both.

BLS lists handheld GPS units and robotic total stations among the instruments surveyors use in the field, and Caltrans describes one stakeout workflow that ends at either device: computations are generated in the data collector and sent to the total station or the GNSS receiver.

They measure in different directions.

A GNSS receiver computes positions from satellite signals; a total station measures angles and distances from its set-up point and lets the collector build positions from that geometry.

GPS.gov notes that the accuracy a GNSS receiver actually delivers depends on satellite geometry, signal blockage, atmospheric conditions and receiver design and quality — and a total station measures along its line of sight instead.

Which instrument leads comes down to the site: what blocks the sky, what blocks the sight line, and the accuracy the job demands.