Setting out is a topographic survey run in reverse
On a topo survey we walk a site, measure what is there, and hand back coordinates. Setting out is the mirror image: we are handed coordinates from the design model and we put them on the ground, point by point, so the gang can pour, weld, and fix to a mark they can trust. It sounds simpler than it is. The moment a steel fixer or a formwork carpenter builds to a peg, that peg becomes the design — there is no second chance once the concrete cures. So our whole method is built around one idea: never let an unchecked number reach the ground.
In practice the failures we see on site are almost never the instrument's fault. They are a station occupied on a disturbed nail, a backsight read to the wrong prism, a setting-out list still in the contractor's local grid while the model is in the project datum. The millimetres the total station can resolve are worthless if the framework around them is wrong. This article walks through how our field teams set out — control first, a checked occupation second, and an independent verification on every committed point before anyone commits material to it.
What sits behind the peg
- 90
- Instruments in our fleet
- total stations, GNSS, scanners, levels
- 1,000+
- Survey projects delivered
- set-out among them on roads & structures
- 3000+ km
- Roads set out & surveyed
- alignment, chainage and offset control
Control before coordinates
Before a single design point is staked, we establish or recover a site control network — a set of permanent, well-spaced reference marks whose coordinates are fixed in the same datum and projection as the design. This is the part clients are tempted to skip, and it is the part that quietly ruins jobs. If the model is on the project's grid and the control is on a different datum or an un-applied projection, every stake is shifted by a consistent amount — sometimes millimetres, sometimes whole metres — and the error is invisible until two trades clash on site.
We tie the control to the project's declared coordinate reference system and check it for internal consistency: bearings and distances between marks must reproduce within tolerance. On larger structures we densify with extra reference nails so that wherever the instrument stands, it can see at least two of them. That redundancy is not bureaucracy — it is the only thing that lets us prove an occupation is good rather than hope it is.
How we set out a point we can defend
- 1
Load the design coordinates from the model and reconcile the datum and projection against the site control — confirm both are on the same coordinate reference system before anything else.
- 2
Recover the control marks on site, inspect each for disturbance, and reject any nail that is loose, painted-over, or doesn't agree with its neighbours.
- 3
Occupy a station: set up over a known mark or free-station from several, level carefully, and measure the instrument height if it matters to the work.
- 4
Backsight a known reference, then independently check into a second known point — the measured bearing and distance must agree with the published values before you proceed.
- 5
Stake each design point by coordinate, marking it clearly with peg, nail, or paint and labelling the point ID so the trade can find it.
- 6
Verify independently: re-observe the staked point, or check it from a second station, and confirm it falls within the agreed tolerance.
- 7
Record the as-staked coordinates, the residuals, and the control used, so the set-out is traceable if anything is queried later.
Choosing the method for the tolerance
| Criterion | Total station on control | RTK GNSS |
|---|---|---|
| Typical point precision (illustrative) | ±2–5 mm | ±15–25 mm |
| Needs sky view / no overhead obstruction | No | Yes |
| Best for structural & tight-tolerance work | Yes | Limited |
| Speed over open ground (bulk earthworks) | Slower | Faster |
Precision figures are typical/illustrative ranges for healthy, field-tested instruments, not a guaranteed spec — see the standards note below.
Typical positioning precision by method (illustrative)
Prove the instrument, don't assume it
Per ISO 17123, a total station's angular and distance performance should be confirmed by a defined field-test procedure rather than taken on faith from the brochure. We field-test instruments on a baseline before precision set-out and after any knock or transport shock. A ±2–5 mm total station only delivers ±2–5 mm if it has been checked, levelled, and pointed at the right prism — the standard exists precisely because instruments drift and operators err.
The instrument at the point of truth
The instruments we point at the tolerance
From our field work
Total stations
Precision angle and distance measurement for control networks, layout, and as-builts.
such as Leica TS16, Viva TS, Topcon ES-series
Total stations from our fleet — field-tested before precision set-out — are the workhorse for construction layout where millimetres matter.
References
- ISO 17123 series — Field procedures for testing geodetic and surveying instruments — International Organization for Standardization (ISO)
- International Federation of Surveyors publications on professional and cadastral standards — International Federation of Surveyors (FIG)
