What VRS is and why it exists
VRS stands for Virtual Reference Station. It is a network RTK technology that makes your receiver work as if a physical base station were located just beside you, wherever you are within the correction network's coverage area.
With a normal single-station NTRIP mountpoint, your rover receives corrections from one physical reference station. That station can be 20, 40 or even 60 kilometres away. As the baseline gets longer, the atmospheric conditions at your rover become less like those at the station. Ionospheric and tropospheric errors then make RTK initialisation slower and a Fixed solution less stable.
VRS solves that problem on the server. It combines observations from several surrounding reference stations, models the conditions at your location and sends a synthetic RTCM correction stream. To your receiver, it looks exactly like corrections from a nearby base station.
1–2 km
Typical effective VRS baseline
3+
Reference stations used around you
GGA
Position message required by VRS
RTCM3
Correction format your rover receives
How VRS works
VRS is a server-side calculation that runs invisibly behind your NTRIP connection. The sequence is straightforward:
Connect to a VRS mountpoint
Your NTRIP client connects to the correction service and sends an NMEA GGA sentence with its approximate position. This two-way communication is what makes VRS different from a normal single-station stream.
The server places you in the network
The VRS server uses your GGA position to identify the physical reference stations around you. It typically selects three or more nearby stations to build the correction model.
Atmospheric conditions are modelled
The server interpolates the ionospheric and tropospheric differences observed across those stations. It estimates the errors that apply at your exact working location.
A virtual station is created
The server synthesises an RTCM3 stream as if a base station existed only a kilometre or two from your rover. No physical hardware is installed at that virtual location.
Your receiver computes RTK normally
Your receiver processes the VRS corrections like any other RTCM3 stream. It does not need to know whether the corrections came from a real or virtual station; it simply benefits from the short effective baseline.
VRS changes the effective baseline, not your equipment
You still use the same rover, field software and NTRIP credentials. Select a VRS mountpoint and transmit GGA; the network does the additional calculation for you.
Standard mountpoint vs VRS
Both options use the same correction network. The important difference is how the correction stream is made.
Standard mountpoint
VRS mountpoint
Correction source
One physical reference station.
A virtual station calculated from multiple physical stations.
Effective baseline
The actual distance to the selected station. It may be tens of kilometres.
Usually around 1–2 km, even when physical stations are far away.
GGA transmission
Usually not required.
Required so the server can generate corrections for your location.
Working over a large area
You may need to change mountpoints as the nearest station changes.
The network adapts to your position automatically.
Fix reliability at long distances
Can degrade as atmospheric differences increase.
Typically faster to initialise and more stable across the network.
When to use VRS — and when not to
Use VRS beyond 20–30 km
Once the nearest physical station is more than roughly 20–30 km away, a VRS stream reduces the baseline-related errors that can keep a receiver in Float or make Fix drop.
Use VRS when moving across a region
For work that covers a large area in one day, VRS follows your approximate location. You do not need to keep choosing a different physical station as you travel.
Use VRS for unstable Fix
If your sky view and connection are good but Fix repeatedly drops on a standard mountpoint, switching to VRS removes baseline length as a likely cause.
Use VRS during disturbed conditions
High solar activity and geomagnetic disturbances increase ionospheric errors. The network model in a VRS service can compensate for spatial differences much better than a distant single station.
A nearby station may be enough
Within about 15 km of a physical reference station, the atmospheric difference is usually small. A standard mountpoint can work just as well and does not depend on GGA.
VRS needs an internet connection
The server must receive your GGA position. Without mobile data at the rover, use a local base and radio link or another correction method that works offline.
The GGA requirement explained
VRS has one requirement that a standard NTRIP connection normally does not: your client must send an NMEA GGA sentence to the caster. GGA includes latitude, longitude, altitude and fix quality. The server uses it to decide which part of its atmospheric model applies to you and where to place the virtual reference station.
The position does not need to be centimetre accurate. A Single or Float position is enough to locate you in the correct network area. However, the GGA must contain a valid position before you connect.
Connected, but receiving 0 bytes per second? Check GGA first.
When GGA is disabled, a connection to a VRS mountpoint can look successful but the caster may send no correction data. Your receiver stays on Single and there may be no obvious error message. Enable GGA transmission, then reconnect.
Wait for a valid initial position
Before connecting, give the receiver 30–60 seconds outdoors to obtain satellite lock. A GGA sentence with zero coordinates can be rejected by the server or place the virtual station in the wrong area.
How to enable VRS on your device
Select the VRS mountpoint supplied by your correction provider, then make sure GGA transmission is enabled. The wording differs slightly by application.
Go to Correction input → NTRIP. Select your provider's VRS mountpoint, enable Send GGA to caster, then connect after the receiver has a Single solution.
VRS by another name
VRS is the most common name for network RTK, but it is not the only approach. A sourcetable may also contain these alternatives:
| Name | What it does | What you need to know |
|---|---|---|
| MAC | The caster sends observations from a master station and auxiliary stations; the receiver performs the network calculation. | Common with Leica systems. GGA is not always required. |
| FKP | The caster sends area-correction parameters that the receiver applies to a single-station stream. | An older network format that is less common today. |
| iMAX | A personalised version of the Master-Auxiliary approach. | Functionally similar to VRS for most users. |
| SSR / SSRZ | Separately models satellite orbits, clocks and atmospheric effects. | A newer approach that is becoming more common in modern networks. |
For most users, choose the VRS mountpoint
Unless your receiver or correction provider specifically asks for MAC, FKP or another format, VRS is the practical default. It works with modern RTK receivers and gives you near-local network corrections throughout the covered area.
