GNSS Surveying: The Complete Guide

GNSS (Global Navigation Satellite System) is the umbrella term for all satellite positioning constellations. A surveying receiver tracks signals from multiple constellations at once and computes its position by measuring the travel time of each signal. Where a phone GPS chip is happy with 3–5 metre accuracy, a survey-grade GNSS receiver resolves the carrier phase of the signal and reaches 1–2 centimetres.

There are four global constellations in operation:

Constellation	Operator	Satellites (nominal)	Status
GPS	United States	31	Fully operational
GLONASS	Russia	24	Fully operational
Galileo	European Union	28	Fully operational
BeiDou	China	35+	Fully operational

A modern multi-constellation receiver can see 30–40 satellites simultaneously. More satellites means stronger geometry, faster ambiguity resolution and reliable fixes under tree canopy or near buildings. To check exactly which satellites are above your site at a given time, use our GNSS Mission Planner.

Every GNSS survey uses one of three core methods. The right choice depends on whether you need results in real time, how far you are from a reference, and the accuracy you must certify.

Method	Accuracy	Result timing	Best for
RTK (Real-Time Kinematic)	~1 cm + 1 ppm	Live, in the field	Stakeout, topo, as-built
PPK (Post-Processed Kinematic)	~1 cm + 1 ppm	After download	Drone flights, long baselines, no radio link
Static	~3 mm + 0.5 ppm	After download	Control points, geodetic networks

RTK — real-time centimetres

A base receiver on a known point streams corrections to a moving rover over radio or cellular (NTRIP). The rover applies them instantly and shows centimetre coordinates on the controller. RTK is the workhorse of daily surveying — fast stakeout and topographic capture without any office processing. Its weakness is the 1 ppm baseline term: error grows roughly 1 mm per kilometre from the base, so a 20 km baseline adds ~2 cm.

PPK — same accuracy, no live link

PPK logs raw observations on base and rover and combines them later in software. Because there is no radio link to lose, PPK is more robust over long baselines and is the standard for drone photogrammetry, where the receiver is on a moving aircraft. You trade real-time feedback for resilience.

Static — the highest accuracy

For control points and geodetic networks, receivers occupy points for 20 minutes to several hours, logging continuously. Long occupations average out atmospheric noise and reach millimetre accuracy. Static is how the control framework that every RTK job ties into is established.

The leap from metres to centimetres comes from measuring the signal's carrier wave instead of its code. The GPS L1 carrier has a wavelength of about 19 cm; the receiver can track its phase to better than 1% of a cycle — roughly 2 mm. The catch is the integer ambiguity: the receiver knows the fractional phase but not how many whole wavelengths lie between satellite and antenna.

Resolving that integer is called getting a fixed solution. Until the ambiguities are fixed you have a float solution good to decimetres only. A healthy RTK setup fixes in seconds. If you are stuck in float, it usually means weak geometry, multipath, or too few common satellites — covered in the error section below.

You don't always need your own base. A CORS (Continuously Operating Reference Station) network is a grid of permanent GNSS stations broadcasting corrections over the internet via the NTRIP protocol. Connect your rover to the nearest mountpoint and you get RTK with no base setup at all.

Network solutions like VRS (Virtual Reference Station) interpolate a correction for your exact location from several surrounding stations, which flattens the 1 ppm distance error across the whole network. Many national networks are free or low-cost. Browse stations near you with our CORS Station Finder, and check our Country Surveying Profiles for the official network and datum in each country.

Centimetre accuracy is only real if you control the error budget. These are the sources that matter in the field, ranked by how often they bite:

Error source	Typical impact	Mitigation
Multipath (signal bounce)	cm to dm	Avoid walls/water; use a ground plane; re-occupy
Ionosphere	scales with baseline	Dual-frequency receiver; shorter baselines
Troposphere	cm in height	Models; avoid extreme elevation differences
Poor geometry (high PDOP)	cm to dm	Plan with a mission planner; wait for better window
Antenna phase centre	mm to cm	Use correct antenna model; measure height carefully

Multipath is the field surveyor's most common enemy — signals reflecting off buildings, vehicles or water arrive late and corrupt the measurement. The fix is situational awareness: keep the antenna clear of reflective surfaces and re-occupy critical points after the geometry changes. Geometry is quantified by PDOP (Position Dilution of Precision); below 2 is excellent, above 6 is poor. A good window is something you plan, not something you hope for — that is exactly what the Mission Planner is for.

1. Plan the window. Check satellite count and PDOP for your site and time in the Mission Planner. Avoid windows with fewer than 7 satellites or PDOP above 4.
2. Establish or connect to a reference. Set a base on a known control point, or connect to a CORS mountpoint via NTRIP.
3. Confirm the datum. Make sure the rover, the corrections and your deliverable all share one datum and projection. Look up codes in the EPSG Explorer and transform with the Coordinate Converter.
4. Wait for a fixed solution. Never record on a float. Confirm the controller reports FIXED and the precision estimate is within tolerance.
5. Measure with redundancy. Occupy control twice, ideally at different times of day, and compare. Agreement under 2 cm is your proof of quality.
6. Check tie points. Re-shoot a known point at the end. If it still matches, the whole session is trustworthy.

If your job involves levelling or orthometric heights, remember GNSS gives ellipsoidal height — you need a geoid model to get elevation above sea level. See the Coordinate Systems guide for the datum side of this, and the Tide & Datum Reference for vertical datums near the coast.

Match the receiver to the job rather than the badge on it. The features that actually move accuracy and productivity are:

• Multi-constellation, multi-frequency — track GPS+GLONASS+Galileo+BeiDou on L1/L2/L5. This is the single biggest driver of reliable fixes.
• Channel count — more channels means more signals tracked at once.
• IMU tilt compensation — lets you measure without levelling the pole, a real speed gain on topo.
• NTRIP / network RTK support — to use CORS networks directly.
• Logging for PPK/static — raw observation logging if you need post-processing.

Compare specs across brands in our surveying instruments database and the manufacturers directory. For terminology, the surveying glossary defines every acronym used here.