VRS — Virtual Reference Station — is the technology that makes an NTRIP network behave as if a real base station is standing right next to you, wherever you are in the network coverage area. It solves the baseline problem completely, and it is easier to enable than most people expect.
In a standard NTRIP setup, your rover connects to the nearest physical reference station in the network. That station might be 20, 40 or even 60 kilometres away. The farther you are, the more the ionosphere and troposphere diverge between your location and the station — and the harder it becomes for your receiver to maintain a stable RTK Fix.
VRS solves this by doing the computation on the server side. The NTRIP server takes data from multiple surrounding physical stations, models the atmospheric conditions across the entire area between them, and generates a synthetic correction stream — as if a perfect base station existed at a point just 1–2 kilometres from your rover. Your receiver receives this stream exactly like it would receive corrections from a local base station, without knowing or caring that no physical station is there.
Standard NTRIP vs VRS
Same rover, same network — different effective baseline
Standard mountpoint
Station A
B
C
You
Effective baseline~42 km
Fix stabilityMarginal
VRS mountpoint
Station A
B
C
Virtual station
You
Effective baseline~1 km
Fix stabilityExcellent
How VRS works
VRS is a server-side computation that runs invisibly behind your NTRIP connection. Here is the sequence from the moment you connect:
1
You connect to the VRS mountpoint
Your NTRIP client connects to the server and sends an NMEA GGA sentence containing your approximate position — typically from a single or float solution. This is the key step that distinguishes VRS from standard NTRIP.
2
The server locates you within the network
The VRS server receives your GGA position and identifies which physical reference stations surround you. It selects the three or more nearest stations whose data it will use to generate your virtual correction.
3
Atmospheric modelling across the network
The server computes the ionospheric and tropospheric conditions at your specific location by interpolating the differences observed between the surrounding physical stations. This modelling is what makes VRS fundamentally different from simply using the nearest station — it actively corrects for the atmospheric conditions at your exact position.
4
A virtual station is generated at your location
The server synthesises an RTCM3 correction stream as if a physical reference station existed 1–2 km from your rover. This virtual station uses the modelled atmospheric data to produce corrections that are far more accurate than what the actual nearest station could provide at distance.
5
Your receiver achieves Fix as if next to a local base
Your receiver processes the VRS corrections exactly like standard RTCM3. From the receiver's perspective it has a base station nearby — it has no way to distinguish a VRS stream from a real local station. Fix initialisation is fast, and Fix stability is high throughout the network coverage area.
When to use VRS — and when not to
📏
Use VRS
Baseline to nearest station is over 20–30 km
Beyond 30 km, standard mountpoints give degraded accuracy and unstable Fix. VRS reduces the effective baseline to under 2 km regardless of where you are in the network.
🗺️
Use VRS
Working across a large area in one day
When you drive across a region and the nearest physical station changes throughout the day, VRS adapts automatically. You always get near-local corrections without managing which mountpoint you are closest to.
📉
Use VRS
Fix is unstable on a standard mountpoint
If you are in network coverage but Fix keeps dropping, switching to VRS is often the fastest fix. It eliminates baseline as a contributing factor immediately.
🌤️
Use VRS
Working during high solar activity
During solar maximum or geomagnetic storms, ionospheric errors increase sharply with baseline distance. VRS's atmospheric modelling compensates for this far better than a distant single station.
📍
VRS not needed
You are within 15 km of a physical station
At short baselines the atmospheric difference between you and the station is negligible. A standard mountpoint works equally well and avoids the GGA requirement.
📵
VRS not possible
No internet connection at the rover
VRS requires a two-way connection — the server needs to receive your GGA position. Without internet, only a standard single-station NTRIP or own base station works.
The GGA requirement explained
VRS has one requirement that standard NTRIP does not: your NTRIP client must send an NMEA GGA sentence to the server. The server uses this sentence to know where you are so it can generate the virtual station at the right location.
GGA contains your latitude, longitude, altitude and fix quality. It does not need to be centimetre-accurate — a single or float position is sufficient to locate you within the network. The VRS server only needs to know which cells of its atmospheric model apply to your area.
VRS returns no data if GGA is not sent
If GGA is disabled and you connect to a VRS mountpoint, the connection appears successful — but the server streams nothing back. Bytes per second will show zero. Your receiver stays on Single. There is no error message. If this happens, enabling GGA is always the first thing to check.
GGA needs a valid position
GGA with all-zero coordinates (0.000°N, 0.000°E) is sent when your receiver has no satellite lock yet. The server may reject this or generate a virtual station in the wrong location. Always give the receiver 30–60 seconds to achieve at least a single solution before connecting to a VRS mountpoint.
How to enable VRS on your device
Enabling VRS involves two things: selecting the VRS mountpoint and enabling GGA transmission. Here is how to do both on the most common devices:
Emlid Flow
› Correction input → NTRIP
› Select mountpoint: RTCM3_NL_VRS
› Enable "Send GGA to caster"
› Connect — wait for single solution first
Trimble Access
› Survey Style → Rover radio
› NTRIP settings: enter VRS mountpoint
› GGA is sent automatically when NTRIP is active
› Dismiss coordinate system warning — normal for VRS
SW Maps
› Settings → NTRIP Client
› Select VRS mountpoint from source table
› Enable "Transmit GGA"
› Tap Connect
FieldGenius Android
› Set Up Corrections → RTK via Internet
› Add New Source → select VRS mountpoint
› Enable GGA transmission in data link settings
› Antenna height → Connect
DJI Pilot app
› RTK Settings → Custom Network RTK
› Enter VRS mountpoint: RTCM3_NL_VRS
› DJI sends GGA automatically after GPS lock
› Must be outside — DJI will not send GGA indoors
Lefebure NTRIP
› Enter host, port, VRS mountpoint
› Enable "Send GGA" in app settings
› Set GGA source to receiver or internal GPS
› Connect
VRS by another name — MAC, FKP, iMAX
VRS is the most widely used network correction technology, but it is not the only one. Different NTRIP software vendors have developed their own variants. All of them solve the same baseline problem with slightly different mathematical approaches. If you see these terms in a sourcetable, they are VRS equivalents:
Name
Full name
Developed by
How it differs
VRS
Virtual Reference Station
Trimble
Server generates a synthetic RTCM stream at the rover's location. Requires GGA.
MAC
Master-Auxiliary Concept
Leica
Server sends raw observations from multiple stations. Receiver does the network computation locally. No GGA needed.
FKP
Flächen-Korrektur-Parameter
Various
Server sends area correction parameters as RTCM messages. Receiver applies them to the nearest single-station correction. Older format, less common now.
iMAX
individualised Master-Auxiliary
Fugro
Variant of MAC with server-side individualisation. Functionally similar to VRS for the end user.
SSRZ / SSR
State Space Representation
Various
New generation format that separately models orbits, clocks, ionosphere and troposphere. Increasingly common in modern networks.
For most users: just use VRS
Unless you are using a Leica receiver with a MAC-specific network or a specialist network requiring FKP, the VRS mountpoint is the right choice. It works with every modern RTK receiver and delivers the same accuracy improvement as all other network correction methods.
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