GPS surveying works by measuring satellite signals with survey-grade GNSS receivers, then correcting the raw position with data from a second receiver or a network of fixed stations.
A base on a known point feeding a rover can produce real-time positions at centimeter level; logged static data can be post-processed with NOAA CORS Network data.
This guide walks through the equipment, the methods and the accuracy each one reaches.
What is GNSS surveying?
GNSS — Global Navigation Satellite System — is the umbrella term for the satellite constellations a positioning receiver can use, and GPS is the United States constellation among them.
GPS.gov lists the other global systems as GLONASS (Russia), Galileo (European Union) and BeiDou (China), plus the regional systems QZSS (Japan) and NavIC (India).
The GPS constellation is built with redundancy.
The United States commits to keeping at least 24 operational GPS satellites available 95% of the time, and GPS.gov counted 31 operational satellites as of July 3, 2023, in medium Earth orbit at about 20,200 km.
A receiver positions itself by tracking those signals and computing ranges to the satellites above it.
How accurate the raw result is depends on satellite geometry, signal blockage, atmospheric conditions and the design and quality of the receiver — the accuracy factors GPS.gov itself lists.
On this page, "surveying by GPS" means survey-grade GNSS.
GPS.gov says most survey-grade receivers use two GPS frequencies, L1 and L2, and that high-end users with dual-frequency receivers and/or augmentation can get real-time positions within a few centimeters.
One date explains why civilian accuracy supports measurement work at all: Selective Availability, the intentional degradation of civilian GPS accuracy, was switched off on May 1, 2000, and GPS III satellites are being built without it.
GPS.gov's framing of what the method changed is promotional, but it is the agency's own summary: GPS-based data collection is much faster than conventional surveying and needs less equipment and labor.
The same page puts a headline on it: a single surveyor can now accomplish in one day what once took an entire team weeks.
How is survey-grade GPS different from a phone or handheld?
Start with the phone, because that is the accuracy everyone has felt.
GPS.gov puts smartphone positioning at about 4.9 m (16 ft) under open sky, and worse near buildings, bridges and trees.
Survey-grade receivers close that gap with hardware and corrections.
Per GPS.gov, most survey-grade receivers track two GPS frequencies, L1 and L2, and users with dual-frequency receivers and/or augmentation can get real-time positions within a few centimeters.
Augmentation is its own layer in that sentence.
WAAS — a satellite-based augmentation system the FAA operates — is designed for aircraft navigation but available in many other receivers.
Conditions still set the ceiling.
GPS.gov lists satellite geometry, signal blockage, atmospheric conditions and receiver design and quality as what received accuracy depends on, which is why the same receiver behaves differently in an open field than under canopy or near buildings.
The signal side is changing too.
GPS is adding three new civil signals — L2C, L5 and L1C — alongside the legacy L1 C/A signal, and GPS.gov notes users must upgrade equipment to benefit from them; L2C was still listed as pre-operational.
Of the new signals, L2C matters to crews working cover: GPS.gov says it broadcasts at higher effective power than the legacy L1 C/A signal, making it easier to receive under trees.
The practical line for a technician: the receiver tier sets what the hardware can do, and the observing method sets what a shot actually delivers on the site.
What are the main methods: static, RTK, network RTK, PPK?
The methods below share the same ingredients: receivers logging satellite data, control to tie the work to, and a choice between corrections computed in real time and positions computed after the fact.
The four names cover the variations.
Static.
Receivers sit still on fixed points and log satellite data together for a whole session, and the positions are computed afterward.
NGS's free OPUS service (Online Positioning User Service) accepts static files of 15 minutes to 48 hours that cross UTC midnight no more than once, then emails back the computed NSRS position.
OPUS splits the work by file length: files of 2 to 48 hours process as static through NGS's PAGES software.
Files of 15 minutes to 2 hours process as rapid-static through OPUS-RS, which has stricter data continuity and geometry requirements and may not work in some remote areas.
RTK (real-time kinematic).
A base receiver on a known point broadcasts corrections to a rover over a radio or modem link, and the rover computes corrected positions on the spot.
NGS's User Guidelines for Single Base Real Time GNSS Positioning (v2.1, 2011) describe the working parameters: base and rover elevation masks between 10° and 15°, and RT1-class work on baselines of 10 km or less.
The single-base radio link has physics of its own.
NGS's guidelines describe a 25-35 watt UHF base radio as FCC-licensed, with a range typically 5-8 km (3-5 miles) in non-rural areas.
Network RTK (RTN).
Instead of running your own base, the rover takes corrections from a network of continuously operating reference stations.
NGS's RTN guidelines (v2.0, March 2011) list the main network correction types as methods such as VRS (virtual reference station), Master-Auxiliary (MAC) and FKP, alongside single-base corrections.
NGS cautions that network coordinates depend on the network's own references: record the datum, adjustment and epoch the RTN uses, and whether it aligns with the NSRS.
Station spacings of 50-70 km were commonly quoted when the guidance was written, with no general rule of thumb.
CORS, the layer underneath.
The NOAA CORS Network (NCN) — continuously operating reference stations managed by NOAA's National Geodetic Survey — provides GNSS data surveyors use to improve positions and tie work to the NSRS.
Its stations are independently owned and operated by partner organizations, which share their GNSS data with NGS; NGS analyzes it and distributes it free of charge.
The network is large: as of February 2025, the NCN provided data from about 2,000 active sites contributed by more than 230 organizations.
NGS has also designated 36 federally owned stations as the NOAA Foundation CORS Network, intended to sit no more than 800 km apart.
PPK (post-processed kinematic).
PPK keeps the RTK field shape — a rover moving point to point while a base logs at the same time — but moves the correction to the office: both receivers record raw satellite data during the session, and the solution is computed afterward.
The trade is the one static work already makes: no corrected position on the display while the rod is on the point, in exchange for not depending on a real-time radio or network link in the field.
What accuracy can each method reach?
Accuracy numbers in GNSS arrive with fine print: a specification source, a set of observing conditions and a confidence level.
Each figure below stays attached to the body that publishes it.
RTK, single base — the spec many manufacturers state.
NGS's guidelines (v2.1, 2011) report that many manufacturers state 1 cm + 1 ppm horizontal and 2 cm + 1 ppm vertical at one sigma (68%).
NGS RTK class RT1.
Typical precision of 1-2 cm horizontal and 2-4 cm vertical at 95% — an accuracy that rides on the class's full observation plan.
NGS RTK class RT4.
Typical precision of 0.1-0.2 m horizontal, at a PDOP limit of 6.0.
Post-processed with CORS data.
NGS says the coordinates can approach a few centimeters, horizontal and vertical.
OPUS static submission.
Most positions compute to within a few centimeters under normal conditions; the OPUS-S quality checklist is overall RMS under 3 cm and peak-to-peak errors under 5 cm.
Phone GPS, for contrast.
Typically within about 4.9 m under open sky, per GPS.gov.
That RT1 plan is specific: 180 epochs at 1 second, redundant observations 4 hours apart from different bases, baselines of 10 km or less, at least 7 satellites and a PDOP of 2.0 or lower.
The PDOP limit climbs through the NGS classes — 2.0 for RT1, 3.0 for RT2, 4.0 for RT3 and 6.0 for RT4 — and NGS notes that PDOP² equals HDOP² plus VDOP², with lower values meaning the satellites are spread better across the sky.
The mid-classes carry the most practical instruction.
NGS's RT3 class, with typical precision of 4-6 cm horizontal, says important vertical features such as pipe and structure inverts and bridge abutments should get their elevations from leveling or a total station rather than RTK.
Static work has its own quality gate.
NGS advises waiting a day before submitting to OPUS, because rapid orbits — available at 17:00 UTC the next day — slightly improve accuracy.
OPUS-RS may perform poorly or fail during high ionospheric disturbance or when a strong weather front passes.
NGS's checklist for a good OPUS solution: precise or rapid orbits used, over 90% of observations used, over 50% of ambiguities fixed, and the correct antenna type and antenna reference point (ARP) height entered.
User errors of that kind, NGS warns, cannot be detected.
Real-time work adds a localization step.
A trusted site localization, per NGS, needs the project surrounded by at least four horizontal and four vertical control monuments, forming a rectangle as far as possible.
For control spaced 20 km apart, NGS suggests adjustment residuals under 2 cm horizontal and 4 cm vertical at 95% confidence.
NGS's warning here is blunt: different localizations can result in substantially different position coordinates, so all project work must use the same localization.
NGS's rules of thumb wrap the method together: survey with fixed solutions only, check known points before, during and after sessions, and beware antenna height blunders and multipath.
The fixed part is a definition, not a preference — NGS defines a float solution as one where whole carrier cycles are not yet resolved to integers, and says users wait until the solution shows fixed before taking real-time observations.
Guideline values, not project specifications
What does a GPS crew do on a typical day?
The method sets the day's shape.
Real-time work is a moving day: set up, wait for a fixed solution, log the point, check in against known control, move again.
Static and PPK work is a patient day: place receivers on points, let them log, and leave the computing for the office.
Configuration comes first, and it is where the guideline numbers earn their keep: elevation masks between 10° and 15°, satellite count and PDOP watched against the class limits, and on single-base work a radio link checked for range.
On a network rover the correction source is the network, and its datum, adjustment and epoch become part of the project record.
Localization ties the session to the project.
The crew observes the control around the site — at least four horizontal and four vertical monuments, arranged as a rectangle where the site allows — and the whole project then works on that one localization, because a different one can move the coordinates.
Through the field day the discipline points are NGS's rules of thumb: observe only with fixed solutions, check known points before, during and after sessions, measure antenna heights carefully, and watch for multipath.
Antenna heights get that care for a reason — a wrong antenna type or ARP height is a user error the processing cannot detect.
Vertical work has a boundary drawn by the guidelines: on RT3-class work, important vertical features — pipe and structure inverts, bridge abutments — get their elevations from leveling or a total station rather than the rover, while the guidelines accept RT for horizontal locations.
On a mixed crew, that is the moment the elevation work hands off to the other instrument.
Back at the office, the data work starts: download raw files, back up antenna heights and setup notes, and check static files against the 15-minute-to-48-hour window OPUS accepts before submitting.
NGS advises waiting a day, then reading the solution's statistics — observations used, ambiguities fixed, RMS — against the checklist before trusting the position.
Who does what on the crew is its own topic: the survey technician career guide covers the role, its field and office halves, and the ladder from rod person to party chief.
What GNSS skills do employers expect?
Every task in this guide is a skill you can name on a resume and answer interview questions about.
The core skills come straight from the guideline content: running a base-and-rover or network-RTK session and knowing why the configuration matters, and telling a fixed solution from a float one — then waiting out the float instead of logging through it.
The habits that protect the data belong on that list too: antenna heights measured and recorded carefully, control checked before, during and after a session, and raw files managed so the office can post-process them.
NGS's OPUS guidance is blunt about why — a wrong antenna type or ARP height is a user error the software cannot detect.
The deeper skills go beyond running the receiver: planning a localization around the project's control, and choosing the observing method that matches the accuracy the job needs.
Knowing when GNSS needs another instrument matters too — NGS's own RT3 guidance sends the elevations of important vertical features like pipe inverts and bridge abutments to leveling or a total station.
Datum awareness is the quiet one.
NGS advises recording which datum, adjustment and epoch a network uses and whether it aligns with the NSRS — the habit that keeps coordinates meaning the same thing to everyone downstream of the crew.
Underneath all of it sits the licensure frame.
The NCEES Model Law exempts work by a licensee's employees or subordinates when it includes no final surveying designs or decisions and is done under the licensee's responsible charge and verified by them.
That is the frame crews take GNSS observations within, with the licensed surveyor carrying the final decisions.
If you are building these skills toward your next crew seat, browse survey technician jobs on the board.