Total Station Surveying: Operation, Coordinate Geometry & Setting Out

The total station is the workhorse of modern surveying. Combining an electronic theodolite with an electro-optical distance meter (EDM), it measures horizontal angles, vertical angles, and slope distances simultaneously, computing coordinates, heights, and stakeout data in real time. If you can operate a total station competently, you can handle almost any site surveying task — from topographic survey to precise setting out of complex structures.

Components of a Total Station

• Horizontal circle: Measures horizontal angles (0°–360°)
• Vertical circle: Measures vertical angles / zenith angles
• EDM (Electro-optical Distance Meter): Infrared or laser, measures slope distance to reflector (prism) or reflectorless
• Microprocessor and keyboard: Real-time computation of coordinates, elevation, stakeout data
• Data recorder: Internal memory (5000–30,000 points) or data collector card
• Level compensator: Electronic tilt sensor compensates for minor instrument tilt (±3' to ±6')
• Display: Dual-face display for simultaneous reading by two surveyors

Setting Up the Total Station

1. Set up tripod over station point — legs firmly set in ground, head approximately level
2. Attach instrument to tripod head; coarsely centre using plumb bob or optical plummet
3. Level the instrument:
   • Roughly level using circular (bull's eye) bubble and tribrach footscrews
   • Precisely level using plate bubble / electronic level display in two perpendicular directions
4. Centre precisely using optical or laser plummet over station mark (tolerance: ±1–2 mm)
5. Enter station coordinates and instrument height (HI)
6. Orient instrument: Sight a reference (back-sight) point whose coordinates are known; set horizontal circle to known azimuth or zero

Types of Angle Measurement

Coordinate Computation

Easting:  EP = EA + HD × sin(bearing)
Northing: NP = NA + HD × cos(bearing)
RL:       RLP = RLA + HI + ΔH − HR (target height)
Where:
EA, NA = instrument station coordinates
Bearing = horizontal angle from North (computed from reference bearing + measured angle)
HI = instrument height above ground mark
HR = prism/reflector height above ground point

Free Station (Resection)

When it is not possible to set up over a known point (e.g., dense obstruction, marshy ground), free station allows the instrument to be set up at any convenient point and coordinates determined by observing ≥3 known points:

1. Set up at unknown point, enter initial approximate coordinates
2. Sight and measure to 3 or more known control points
3. Instrument solves for station coordinates using least squares
4. Check residuals (should be <5 mm) and accept solution

Free station is extremely time-efficient and widely used in building construction and underground works.

Setting Out (Stakeout)

Setting out transfers design coordinates from drawings to physical points on the ground. Total station stakeout procedure:

1. Set up at known station, orient to back-sight as above
2. Enter design (stake-out) coordinates of the point to be set
3. Instrument displays: bearing to point and distance
4. Rotate instrument to indicated bearing; place prism on the line
5. Move prism forward/backward until displayed distance matches design distance
6. Mark the physical point (peg, paint mark, nail)

Precision of Setting Out:

Total Station vs GPS/GNSS

EDM Accuracy and Atmospheric Correction

Total station EDM accuracy is expressed as: ±(a mm + b ppm × D)
Example: Leica TS 06 — ±(2 mm + 2 ppm × D)
At 1000 m: ±(2 + 2) = ±4 mm

Atmospheric corrections for precise work:

• Measure air temperature (°C) and atmospheric pressure (hPa) at time of survey
• Enter into instrument or compute correction: K = 281.8 – (0.29065 P/(1 + 0.003661 T))
• Significant only for distances >500 m; below that, effect is negligible for most engineering work

Frequently Asked Questions