Differential GPS uses reference information to reduce errors in GPS positioning. DGNSS extends the terminology to other satellite constellations. The reference information can come from a local base, a network, or a broader correction service, depending on the method.
A corrected position is still a measurement result with conditions and limitations. Identify the correction method, supported signals, reference frame, and current solution status before treating a displayed coordinate as suitable for a precise task.
How a reference receiver helps
A reference receiver at an established position observes signals affected by satellite and propagation errors. Information derived from those observations can help a rover reduce errors that are sufficiently shared between the sites. NovAtel's DGNSS explanation describes this reference-and-rover principle.
The reference cannot observe every error at the rover. A reflection from a nearby wall, poor rover antenna installation, or a mistaken pole height can remain a problem. Separation, atmospheric conditions, observation quality, and correction age all affect how useful the reference information is.
Choose a method before choosing a connection
| Approach | Basic idea | What to investigate |
|---|---|---|
| Code-based DGNSS | Use reference information to improve code-based positioning. | Coverage, supported messages, and achieved performance. |
| SBAS | Use regional satellite-based augmentation information. | Service area, receiver support, and intended application. |
| RTK or network RTK | Use carrier-phase observations and reference data for a real-time solution. | Initialization, reference coordinates, baseline or network coverage, and correction continuity. |
| PPP | Use precise satellite information and other supported corrections. | Convergence, service availability, supported signals, and receiver implementation. |
| Post-processing | Combine recorded observations with reference data after collection. | Observation completeness, timing, and processing settings. |
Names describe families of techniques, not universal accuracy tiers. Some services combine methods. NovAtel's RTK and PPP discussion is a useful starting point for understanding their different correction architectures. Evaluate the exact service and receiver together.
A data connection is only one part of compatibility
Ntrip carries GNSS data streams over internet protocols. It is a transport mechanism, not an accuracy level. The BKG introduction to Ntrip explains its role in distributing streams. RTCM refers to a family of message standards commonly used for observations and corrections; matching the name alone does not establish message compatibility.
Check the mountpoint or selected stream, required messages, constellations, frequencies, authentication, and whether the service needs an approximate rover position. Keep credentials out of shared logs. A successful connection can still deliver data the receiver cannot use.
For an outage test, log when the last usable correction arrived, how the receiver's solution status changes, and what the application displays. Set acceptance rules from the job requirements and documented receiver behavior. There is no single correction-age cutoff that suits every method.
Check current service availability
The U.S. Nationwide Differential GPS service was discontinued on June 30, 2020, according to GPS.gov's augmentation overview. An old receiver's beacon capability therefore does not establish access to a current U.S. NDGPS service. Other regions and service types require their own checks.
Confirm coverage from the operator, receiver and antenna compatibility from the manufacturer, and access terms before planning fieldwork. A receiver that supports an augmentation does not automatically include any required account, communications hardware, or subscription.
Ask what happens outside coverage and after an interruption. Some workflows can log observations for later processing, but that requires appropriate data collection in advance. A saved list of latitude and longitude points is not equivalent to raw GNSS observations.
Verify the result against independent evidence
In RTK, a fixed solution indicates that carrier-phase ambiguities have been resolved as integers under the receiver's algorithm. It is valuable status information, but it does not establish that the base coordinate, antenna height, or project reference system is correct.
Check an independent control point, repeat observations under the project's procedure, and retain the solution reports. A repeatable offset can be a setup or reference-system problem even when successive positions agree closely. GPS Surveying explains what belongs in that record.
AI can organize correction logs and compare status changes, provided timestamps and field meanings are explicit. Use it to highlight intervals requiring review. It should not relabel float or standalone observations as fixed, or manufacture corrections for gaps.