TL;DR: A survey control network is the framework of permanently marked, precisely coordinated points that every measurement, set-out and monitoring task on a site connects back to. This survey control networks FAQ answers the questions we field most from mine surveyors, project engineers and site managers — covering accuracy classes, the GDA2020 and AHD datums, ICSM standards, costs and maintenance — so you can specify control correctly the first time.
Key takeaways
- Australian control is classified under ICSM SP1, from Zero Order (±1 mm relative, used for deformation monitoring and mill alignment) to Third Order (±50 mm, general earthworks); specify the order your tightest tolerance actually needs, not the highest available.
- Horizontal positions are referenced to GDA2020 / MGA2020 and heights to AHD; legacy sites still on GDA94 must be transformed, not assumed, because the two datums differ by roughly 1.8 m.
- A complete network is layered — primary control on stable ground (200–500 m spacing), secondary for daily work (50–150 m), and tertiary set-out points re-established as the site changes.
- Establishment typically costs 5–10% of total survey spend (roughly AUD $3,000 for a small Third Order site to $40,000+ for a large First Order network), yet a control failure can invalidate months of downstream work.
- Control degrades through blasting, settlement, vibration and theft; primary marks should be re-observed quarterly on active mines and after every breakthrough on tunnels.
Datums, standards and accuracy
What datum and coordinate system are Australian control networks set on?
Horizontal control is referenced to the Geocentric Datum of Australia 2020 (GDA2020), projected into Map Grid of Australia 2020 (MGA2020) zones for working coordinates. Heights are referenced to the Australian Height Datum (AHD). GDA2020 replaced GDA94 to account for the 7 cm/year northward movement of the Australian plate — over the period between the two realisations this accumulates to roughly 1.8 m, so coordinates from an older site cannot simply be reused on a new GDA2020 survey. We transform legacy data using the published seven-parameter or grid transformations rather than treating the difference as negligible. On confined industrial sites a local plane grid is sometimes preferred to avoid scale factor and grid convergence, but we always tie it back to GDA2020 so the work remains integratable.
Which standard governs control surveys in Australia?
Control surveys follow the Intergovernmental Committee on Surveying and Mapping (ICSM) Standard for the Australian Survey Control Network, SP1, which defines accuracy in terms of positional uncertainty (PU, accuracy relative to datum) and local uncertainty (LU, accuracy relative to adjacent marks). For mining, mine surveyors also work within the relevant state mine safety and survey regulations — for example WA's mine survey requirements in the Pilbara goldfields and Bowen Basin coal operations in Queensland. Deliverables are reported with the uncertainty figures, not just coordinates, so the client can verify fitness for purpose.
What accuracy class do I actually need?
The order is driven by your tightest downstream tolerance. As a guide:
| Order | Relative horizontal | Vertical | Typical use |
|---|---|---|---|
| Zero | ±1 mm | ±0.5 mm | Deformation monitoring, SAG/ball mill and kiln alignment |
| First | ±5 mm | ±3 mm | Tunnel and shaft control, major structure monitoring |
| Second | ±15 mm | ±10 mm | Plant set-out, building and mine primary control |
| Third | ±50 mm | ±30 mm | Bulk earthworks, haul roads, topographical pickup |
Specifying Zero Order for a haul road wastes money on monumentation and observation time; specifying Third Order for a rotary kiln alignment will never hold the millimetre tolerances the mechanical fit requires. The surveyor's job is to match the order to the work.
Establishment and equipment
How is a control network established?
The sequence is reconnaissance and design, monument installation, observation, least-squares adjustment, and validation. For primary control we run static GNSS sessions — typically 30 minutes to several hours per baseline depending on length and required order — observed on Trimble R12i or Leica GS18 receivers, then connect to nearby government Permanent Survey Marks where available. Heights are carried by precise differential levelling with invar staves for First Order and better. Secondary and tertiary control are densified by total station (Leica TS16 / Trimble S7) traversing and RTK. Every observation set carries redundancy so blunders are detectable, and the network is adjusted as a whole rather than coordinated point-by-point.
What equipment is used and why does it matter?
Horizontal and vertical control on industrial sites is established with survey-grade GNSS and robotic total stations; where the work feeds equipment alignment or as-built modelling, we integrate Leica RTC360 or FARO Focus laser scanners and DJI Matrice / DJI Mavic 3 Enterprise UAV photogrammetry, all registered onto the same control. Tying scan and drone data to a rigorously adjusted ground network is what keeps a point cloud or orthomosaic dimensionally trustworthy — without it, a scanner quoting 2 mm range noise can still sit 100 mm out in real-world position.
Do you fly drones over control work, and what are the rules?
Yes. UAV survey is governed by the Civil Aviation Safety Authority under CASA Part 101. Commercial operations require a Remote Operator's Certificate (ReOC) and licensed remote pilots, with site-specific approvals for controlled airspace, operations near aerodromes and beyond visual line of sight. On a mine or port the UAV deliverable is only as good as the ground control panels it is georeferenced to, so drone mapping and the control network are planned together.
Cost and maintenance
How much does a control network cost?
Cost scales with area, accuracy, terrain and number of marks. Indicative ranges:
| Scope | Order | Indicative cost (AUD) |
|---|---|---|
| Small site (<5 ha) | Third | $3,000–$8,000 |
| Medium site (5–50 ha) | Second | $8,000–$20,000 |
| Large site (50–500 ha) | Second | $15,000–$40,000 |
| Major project (500+ ha) | First | $40,000–$100,000+ |
| Tunnel/shaft transfer | First | $15,000–$50,000 |
| Deformation control | Zero | $20,000–$80,000 |
Establishment is usually 5–10% of total survey cost. Re-establishing control after a failure — once it has been used for months of set-out — routinely costs five to ten times the original investment, which is why control is the highest-return line item in most survey budgets.
How often does a control network need to be re-checked?
Often enough to catch movement before it propagates into your work. On active open-pit and underground mines, primary control should be re-observed quarterly because blasting, excavation and ground settlement shift marks. Tunnel control is re-checked weekly or after each breakthrough. Building sites warrant monthly checks during active construction, and long-term infrastructure annually. Deformation networks run to a fixed schedule set by the monitoring brief, from weekly to annually.
Frequently asked questions
What is the difference between a control point and a benchmark?
A control point has a known horizontal position (easting and northing) and may also carry an AHD height. A benchmark is specifically a height reference used for levelling. Every benchmark is a control point for height, but not every control point is a benchmark.
Can I use existing government survey marks instead of paying for new control?
Where they are accessible and of suitable order, yes — government Permanent Survey Marks give you a direct, defensible tie to GDA2020 and AHD. In practice they are usually too sparse for site work, so we connect to them and densify with project-specific marks between them rather than relying on them alone.
Why does the control matter if my laser scanner is already accurate to 2 mm?
Instrument precision and positional accuracy are different things. A scanner can resolve fine detail yet still place the whole cloud tens of millimetres out of true position if it is registered to weak or inconsistent control. The control network is what guarantees that today's scan aligns with last year's as-built and next year's expansion design.
What happens when control points are destroyed by mining or construction?
We design networks with redundancy and place primary marks outside active zones so the network survives the loss of individual points. When a mark is lost, surviving points let us re-establish it without re-surveying the whole site — provided the network was properly adjusted and documented in the first place.
How long does establishment take?
A small site can be controlled in one to two days. A large, high-order network may take one to two weeks of field observation plus adjustment and reporting time, depending on point count, accuracy, terrain and weather.
Whether you are standing up control for a new Pilbara iron ore pit, a Bowen Basin coal expansion, a Gladstone processing plant or a Hunter Valley shutdown, getting the network right is the cheapest insurance on the project. To discuss accuracy requirements, datums and a fixed-scope quote, call Industrial Spatial Solutions on 0407 057 015 — we design, establish and maintain control networks to ICSM standards across Australia.
Related reading: Control network surveys, How to establish a survey control network