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Frequently Asked Questions
What is the difference between a survey instrument and a measuring tool?
A measuring tool gives a dimension between two points you can see. A survey instrument gives a coordinate - a position within a defined reference frame - which can be compared against a design model, recorded, and reoccupied later. That is what makes setting out and as-built verification possible.
When should I use a total station rather than GNSS?
Indoors, in tight urban sites, under structure, in tunnels, and anywhere the sky is obstructed or the accuracy required is tighter than GNSS will reliably give. A total station needs line of sight and a known setup, but within those constraints it is more accurate and entirely independent of satellite conditions.
When is GNSS the better choice?
On open sites - groundworks, roads, drainage, topographic survey - where clear sky is available and points are spread over a wide area. One person can work alone without line of sight between points, which is a large productivity gain over a total station needing repeated setups and sight lines.
Do I need both?
Most contractors doing varied work end up with both, because the choice is driven by the environment rather than by accuracy. A site that starts as open groundworks and becomes a building with an interior will need GNSS first and a total station later, and neither covers the whole job well.
What accuracy can I expect?
A total station measures angles to a few seconds of arc and distances to a few millimetres, giving millimetre-level positions at working ranges. Network RTK GNSS typically achieves centimetre-level horizontally with vertical accuracy noticeably worse. Quoted figures assume good conditions and correct setup, both of which dominate real results.
What training do these instruments need?
More than the hardware suggests. The instruments are straightforward to operate, but the coordinate systems, projections, control setup and error checking behind them are where mistakes are made and where they are expensive - a correctly operated instrument on a wrongly established control point produces confidently wrong results.
Do these need calibration?
Yes, periodically and after any knock. Total stations need collimation and compensator checks, which can be performed in the field, plus periodic laboratory calibration. GNSS receivers need far less, but pole and tribrach condition matters greatly, since a bent pole or an out-of-adjustment bubble corrupts every reading.