How to Configure NTRIP on a GNSS RTK Receiver (2026 Guide)

NTRIP stands for Networked Transport of RTCM via Internet Protocol. It is the standard method for delivering GNSS differential correction data from a permanent CORS (Continuously Operating Reference Station) network to your RTK rover via the internet.

How It Works. A CORS network operates a grid of permanently installed GNSS reference stations at precisely known positions. Each station continuously measures GNSS errors and transmits correction data to a central NTRIP caster server. Your RTK receiver connects to that server via mobile data (4G/LTE), selects a correction stream (mountpoint) from a reference station near your location, and applies those corrections in real time to resolve the carrier-phase integer ambiguities needed for Fixed solution.

Key Terms. NTRIP Caster: the server that distributes corrections. Mountpoint: a specific correction stream from one reference station or a virtual reference station (VRS). RTCM: the correction data format (RTCM 3.2 preferred). Differential age: time since the last correction message was received — must stay below 3 seconds.

Before opening ApekSurv, confirm you have all four requirements.

1. CORS Credentials. Username and password issued by the CORS network operator (e.g., INEGI for Mexico, NRIAG for Egypt, InaCORS for Indonesia, DLD for Dubai). Registration typically takes 3–10 working days. Apply before mobilising to site.

2. SIM Card with Mobile Data. Insert a local SIM card with an active mobile data plan into the receiver's SIM slot. Confirm the correct APN is set for your operator — wrong APN settings prevent data connection even when voice works. Common APNs: Telcel Mexico = internet.itelcel.com; Telkomsel Indonesia = internet; Etisalat UAE = internet; Vodafone Egypt = internet.vodafone.net.

3. CORS Server Address and Port. The server address (e.g., ntrip.inegi.org.mx) and port number (almost always 2101). Get this from the CORS network's registration documentation.

4. Open Sky View. At least 15° sky view above the horizon in all directions. NTRIP corrections cannot compensate for poor satellite geometry from obstructions.

Distance — Choose the Nearest Station. RTK accuracy degrades with baseline length. Select the mountpoint whose reference station is closest to your current location. Most source tables show station coordinates — use these to identify the nearest station. A baseline over 50 km will degrade Fixed reliability; over 70 km, Fixed is unreliable.

Format — Prefer RTCM 3.2 or 3.3. RTCM 3.2 supports multi-constellation corrections (GPS + GLONASS + BeiDou + Galileo). RTCM 3.3 adds BDS Phase 3 and Galileo HAS support. RTCM 2.x carries GPS-only corrections — using it with a 1408-channel receiver wastes most of your satellite tracking capability.

VRS vs Physical Station Mountpoints. VRS (Virtual Reference Station) mountpoints generate a synthetic correction stream computed for your exact rover location from the surrounding network of real stations. This gives better accuracy than a single physical station, especially when your location is midway between two stations. Select VRS where available.

Naming Conventions. Station names are usually place abbreviations (e.g., MERI for Mérida, JKTB for Jakarta). If the source table shows coordinates, find the station closest to your project location. If no coordinates are shown, use the station name to identify the nearest city.

1. Differential Age — Must Be Below 3 Seconds. Differential age counts up from 0 and resets with each new correction message. If it climbs continuously above 3 seconds and never resets, corrections are not arriving — the connection exists but no data is flowing. Check mountpoint selection and try an alternative mountpoint.

2. Solution Status — Must Reach Fixed. Status should progress: Single → Float → Fixed. Float to Fixed typically takes 10–30 seconds in open sky. If it stays in Float for more than 2 minutes, check sky obstruction, differential age, and baseline distance to the reference station.

3. Check Against a Known Point. Before recording any data, navigate to a known physical control monument and verify the displayed coordinate matches within 20 mm. If the difference is larger, the coordinate system or datum settings in ApekSurv may be wrong — not the NTRIP connection.

NTRIP is ideal where CORS coverage and reliable mobile data exist. However, there are clear situations where deploying your own base station is the better choice. If you are working in a remote area with no cellular signal, or if the nearest CORS reference station is over 70 km away, Base+Rover using a MAX5 receiver as the base gives you complete independence — corrections are transmitted locally via UHF radio with differential age below 0.5 seconds and no dependence on internet infrastructure. The same applies on sites where cellular coverage is intermittent or during critical high-precision work where a direct local baseline of a few kilometres delivers superior repeatability. A MAX5 base and any APEKS rover also remove the need for CORS registration and subscription, making it the fastest way to start surveying on a new site.