How to Configure NTRIP on an RTK Rover: Step-by-Step Setup Guide

Table of Contents

• What is RTK?

• What is NTRIP?

• NTRIP setup procedure for an RTK rover

• Precautions when using NTRIP

• Simple surveying with LRTK

• FAQ

RTK surveying is a technique that uses GNSS (satellite-based positioning) to perform high-precision positioning in real time. Whereas traditional standalone positioning (ordinary GPS) can have errors on the order of several meters, RTK achieves centimeter-level accuracy by transmitting correction information from a base station (base) to a rover to correct those errors. This article explains the basics of RTK surveying and focuses in particular on how to configure an RTK rover to use NTRIP corrections. To make it easy for beginners to understand, we will explain what NTRIP is, the required connection information (host name, port number, mount point, etc.), and the step-by-step procedure. At the end of the article, we also introduce simple surveying using "LRTK" as a solution that makes achieving this high-precision positioning easier.

What is RTK?

RTK (Real Time Kinematic) positioning is a positioning method that uses two GNSS receivers to perform real-time error correction. One is operated as a base station (base station) installed at a known, accurate coordinate, and the other as a rover station (rover station) that moves to the point to be positioned. It is characterized by using the differences in satellite signals received simultaneously by both receivers to calculate the rover's position with high precision. Errors of approximately 5–10 m (16.4–32.8 ft) that occur in standalone positioning can generally be reduced by RTK to within a few centimeters (within a few inches). For this reason, RTK has begun to be used in fields that require precise positional information, such as autonomous drone navigation, machine guidance for construction equipment, and civil engineering surveying.

To perform conventional RTK positioning, you had to provide your own base station. You needed to set a GNSS receiver for the base station at a point with known coordinates and transmit correction data to the rover via radio, which incurred the effort and cost of installing a base station for each site. In particular, in surveys over wide areas, accuracy decreases as you move away from the base station. However, in recent years, network RTK has become widespread as a solution to this problem. This method uses correction information obtained from multiple reference-station networks (electronic reference points such as CORS and private reference-station networks) established by governments or companies across the country, accessed via the Internet. Because users can perform RTK positioning with only a rover and without installing their own base station, on-site preparations are greatly simplified. Using data from multiple reference stations also helps limit accuracy degradation over long distances.

What is NTRIP?

A representative method for delivering correction information in network RTK is NTRIP (Networked Transport of RTCM via Internet Protocol). Simply put, NTRIP is a communication protocol for exchanging RTK correction data over the Internet. It is a mechanism that distributes GNSS positioning data acquired at base stations (such as correction messages in RTCM format) over the Internet so that rover units can receive and use them.

The NTRIP system consists of three main components.

• NTRIP Server (Base Station): The GNSS receiver acting as the reference station. It sends its observation data as correction information. This is either the conventional base station itself or a software device connected to the base station.

• NTRIP Client (Rover): The GNSS receiver acting as the rover. It receives correction information via the Internet and applies it to its own positioning solution. The user's RTK-capable equipment or software fulfills this role.

• NTRIP Caster (Distribution Server): An Internet server that acts as an intermediary between base stations and clients. It receives data sent from base stations and forwards it in response to client requests. A caster can be configured with multiple data distribution points, and clients select and connect to the required data (a specific base station's stream) from among them.

NTRIP operates using a mechanism similar to HTTP and often uses a specific TCP/IP port (the standard is 2101). A client connects to the caster with the host address (server URL or IP) and port number, and specifies which base station data to receive using an identifier called a mount point. If necessary, authentication with a username and password can be performed to restrict access. When the caster receives the request (and authentication information) from a client, it begins transmitting the corresponding base station data. This allows the rover to obtain correction information from the base station in real time.

Network RTK correction services are most often provided via NTRIP. If users sign a contract with a service provider in advance and obtain the connection information for the corresponding NTRIP caster, they can start RTK positioning anywhere without a base station. For example, in Japan there are experimental offerings using data from the Geospatial Information Authority of Japan’s GEONET (GNSS Earth Observation Network System) and commercial services provided by private companies. Representative examples include RTK correction services deployed nationwide by telecommunications carriers and paid services offered by surveying-instrument manufacturers. An example is the network RTK correction service “ichimill (Ichimiru)” provided by a telecommunications operator, which installs many of its own GNSS reference stations on company communication towers and other sites and distributes stable correction data nationwide. As a result, users can achieve real-time positioning with cm level accuracy (half-inch accuracy) with only a dedicated terminal and an Internet connection. There are also NTRIP services provided by local positioning service operators and municipalities, which can be selected according to use and region (service fees and coverage areas vary by service).

In summary, using the NTRIP method eliminates the need to install base stations that were previously required, and enables centimeter-level positioning (cm (in)) over a wide area via the Internet. However, because NTRIP generally requires a communications link, separate measures are needed in environments where the cellular network is out of range (countermeasures are described later). On the other hand, systems such as the quasi-zenith satellite's CLAS, which provide correction information via satellite, have also appeared, offering a way to achieve high accuracy without mobile communications. CLAS requires compatible receivers, but it has attracted attention because it can provide positioning accurate to several centimeters (several in) even in situations where communications infrastructure is cut off, such as mountainous areas or disaster sites. Depending on the application, switching between or combining NTRIP and CLAS can help build a more stable RTK positioning environment.

NTRIP Configuration Procedure for RTK Rover

Now, we will explain in detail the connection setup procedure for receiving NTRIP corrections with an RTK rover. Here, we assume using commercially available RTK-capable GNSS receivers or smartphone-connected devices as the mobile station and present the general workflow.

• Preparation of RTK-compatible equipment: First, prepare a GNSS receiver that supports RTK positioning. Recently, various multi-GNSS, multi-frequency receivers that enable high-precision positioning have become available. These include survey instruments with integrated antennas and compact rover units that connect to smartphones and tablets. The important thing is that it supports the NTRIP client function (ability to receive corrections over the internet). Check the specifications to confirm whether your receiver or app is NTRIP-compatible. Also prepare a controller for displaying and operating positioning data (for example, a field tablet or smartphone). Install dedicated positioning apps or software as needed.

• Joining a correction service and obtaining information: Subscribe or register with the NTRIP-format correction service you will use and obtain the information required for connection. Many services provide the following items. - Hostname (or IP address): Example address of the correction data distribution server (e.g., `caster.example.com`) - Port number: The server's port number (often `2101`, but it depends on the service) - Mount point name: Identifier of the reference station data you want to receive (e.g., `BASE01` or `VRS_ALL`) - User ID and password: Authentication information required for the connection if the service is account-based

These pieces of information can be found in the manual provided at the time of contract and on the web management interface. Depending on the service, there may be multiple mount points per region, and you may be advised to select a reference station or virtual reference station (VRS) near your current location. Choose the data stream that corresponds to your desired area. Also, when using public reference stations, such as the Geospatial Information Authority of Japan's experimental services, obtain the connection information after completing the prescribed procedures.

Additionally, prepare a way for the rover-side device to connect to the Internet on site. Specifically, a module with a cellular SIM or smartphone tethering, for example. Please check the network conditions in advance to ensure a stable online connection during outdoor work (if you are out of coverage, an NTRIP connection is not possible). Data usage depends on the correction data stream, but RTK RTCM data is typically a few hundred bytes per second, so a large data allowance is not required in normal circumstances.

• Configure the NTRIP connection on the receiver side: Open the settings screen of the GNSS receiver or the linked app and configure the settings for Network RTK (NTRIP). Labels vary by manufacturer and software, but in general there are menus such as "Network Corrections" or "Ntrip Settings". Enter the host name, port, mount point, and username/password obtained in the previous step. Enter them carefully to avoid typos (IDs and passwords are case-sensitive). After saving the settings, enable the NTRIP client function (e.g., "Receive correction data", "Turn on Network RTK", etc.). Many apps allow you to select your contracted service from a connection list or to manually register a new NTRIP connection.

<small>*(※Some devices have a setting to transmit the rover’s current position information (NMEA-format GGA message) to the NTRIP caster. This is used by network RTK services to generate virtual reference stations and to automatically select the optimal base station. Normally this is done automatically if you follow the service provider’s instructions, but if options such as "Send current position" are turned off, you may not receive corrections properly, so please be careful.)*</small>

• Establishing the connection and starting positioning: After completing the NTRIP settings, start the actual connection. Turn on the receiver to allow satellite positioning and enable the NTRIP connection. If there is a "Connect" button or similar in the settings screen, press it to start. When the connection is successful, correction data will begin flowing in real time from the base station to the rover. Many devices and software display the connection status and should allow you to confirm data reception volume and the base station name. Once you reach this point, pay attention to the quality of the RTK solution. At first it will likely be displayed as Float solution (Float). This indicates that the integer bias—the main source of error—has not yet been resolved, and the accuracy is on the order of tens of centimeters (tens of in). If satellite tracking and correction information are sufficient, the solution will switch to Fix solution (Fix) within tens of seconds to a few minutes. A fix means the integer bias has been resolved, enabling high-precision positioning with horizontal errors of several cm (several in) and vertical errors of several cm to tens of cm (several in to tens of in). The positioning app screen will show status indicators such as "FIX" and "FLOAT" and current accuracy metrics (standard deviation, etc.), so always confirm a FIX before recording positioning results.

• Use of positioning data: With corrections applied, perform the actual surveying work. Set the coordinate system to be used in the surveying software as necessary. In public surveying in Japan, the plane rectangular coordinate system based on the World Geodetic System (Japan Geodetic Datum JGD2011) is often used, so select the applicable system (the zone number for each region). Correction data obtained from NTRIP services are also based on the same reference datum, but occasionally discrepancies due to differences in reference frames may occur. In such cases, configure coordinate transformations in the software (apply origin offsets, geoid height conversions, etc.). Once preparations are complete, begin observation and recording of survey points or machine guidance (for example, position guidance during stakeout or pile-driving work). As long as an RTK FIX solution is maintained, the obtained coordinate values are guaranteed to have real-time centimeter-level accuracy (half-inch accuracy).

• Verification of Results and Backup: After surveying work, verify the collected coordinate data. If it is possible to compare with known points on site, checking whether the errors are within acceptable limits provides reassurance. If there are problems, review the choice of correction service and equipment settings, and re-measure as necessary. Modern high-precision positioning systems also allow the obtained data to be uploaded to the cloud from the field and shared immediately. For example, if you send the measured point coordinates and site photos on the spot, a remote office can instantly check and verify the data. Operating with real-time data sharing and saving in the field reduces post-survey error discovery and the risk of data loss, improving work efficiency.

That concludes the basic setup procedures and workflow. In the next chapter, we will address the key points and precautions to keep in mind when using NTRIP-type RTK.

Important notes when using NTRIP

There are several points to keep in mind for the stable operation of network RTK positioning via NTRIP.

• Securing the communication environment: Since correction data are received via the Internet, the quality of the communication link directly affects positioning stability. If the rover's communications are unstable, correction data can be interrupted, the solution may revert to FLOAT, or in the worst case the RTK solution can be lost and revert to standalone positioning. In urban areas 4G/LTE or 5G connections are generally sufficient, but in mountainous areas or underground a smartphone may have no signal. In such locations, measures such as switching from relying on a virtual reference station service to your own simple base station (local RTK), or considering the use of CLAS mentioned later, are effective. Also, routing network connections through a VPN or similar can introduce significant latency. Because a shift in the timing of applying correction information affects positioning accuracy, it is desirable to keep the communication path as simple as possible and minimize latency.

• Satellite visibility and initialization: A good satellite reception environment is essential for high-precision positioning. If there are many tall buildings or trees nearby, satellite visibility can be blocked and signal reflections can more easily cause multipath interference. Install the antenna in as open a location as possible so it has a wide view of the sky. If your receiver settings include an elevation mask (an angle limit that excludes low-elevation satellites), set it appropriately to reduce the influence of poor-quality signals. Also, if you feel it is taking a long time for RTK to reach FIX after starting, performing a reinitialization (reset) on the receiver may help it reach a FIX solution more quickly. If the solution temporarily reverts to FLOAT during operations, remain calm and wait for several tens of seconds, or try disconnecting and reconnecting once; either action can make it easier to obtain FIX again. Always monitor the status during positioning, and be careful not to use data obtained while in FLOAT lightly (because the errors are large).

• Correction services and baseline distance: RTK corrections from a single base station become harder to maintain accurately as the distance (baseline length) to the rover increases. Generally, a guideline is that distances of several km to the low tens of km can maintain high accuracy. Network RTK services mitigate this issue by using data from multiple base stations, but being extremely far away can still increase the time to achieve an initial fix or otherwise be disadvantageous. If possible, it is effective to choose a correction data stream close to your area of use. When signing up for a service, if there are mount points by area, specify the one nearest your site. Also, for surveying while moving, some services automatically switch to the appropriate correction when your position changes significantly. In that case, note that correct transmission of your own position (the aforementioned GGA transmission setting) is a prerequisite.

• Positioning accuracy and equipment selection: To deliver high-precision positioning performance, the receiver's own capabilities are also important. Devices that are multi-GNSS (using multiple constellations such as GPS, GLONASS, Galileo, QZSS, etc.) and support multiple frequencies can maintain a FIX solution far more stably than single-GNSS, single-frequency units. Most modern RTK receivers have this specification, but if you are repurposing older equipment, check its compatibility. Using a high-performance antenna also reduces noise and multipath effects and contributes to improved accuracy. Additionally, it is a basic but important practice to manage battery levels and prevent overheating (thermal runaway) in the field so that equipment does not suffer performance degradation.

By following the above points, you can maintain higher reliability in NTRIP-based RTK positioning. Next, we will briefly introduce LRTK, a solution that makes such advanced RTK positioning easier to achieve.

Simplified surveying using LRTK

While RTK positioning offers significant benefits, it's also true that there are hurdles such as preparing expensive dedicated equipment and performing specialized setup tasks. The solution developed to address these challenges and allow even beginners to easily use centimeter-level positioning is called LRTK. LRTK is the name of a compact, all-in-one RTK-GNSS receiver device and service developed by a startup originating from Tokyo Institute of Technology. It's a pocket-sized receiver that can be attached to a smartphone (mainly iPhone and iPad) as an add-on, with the antenna, high-precision GNSS chip, communication module, and battery all integrated. It can be easily mounted on the back of a smartphone using a dedicated mount, and it is very lightweight at approximately 125 g. By simply attaching this small device to your smartphone, your handheld smartphone is transformed into a high-precision RTK surveying instrument.

The biggest advantage of using LRTK is its simplicity and responsiveness. Simply launch the dedicated LRTK app, enter the NTRIP correction service information and turn on "Network RTK", and a lone operator can immediately begin centimeter-level positioning. Complex operations are abstracted by the app and completed in simple steps such as "select correction information and start connection". Its intuitive design means even those without specialized knowledge can feel confident when trying RTK for the first time.

The high-precision positioning information obtained with LRTK can be recorded by tagging it to photos taken on a smartphone and to point cloud data. For example, if you take site photos with an LRTK-enabled smartphone, all images will be assigned precise positioning coordinates. This makes it easy to perfectly overlay the photographed images on a map and to immediately utilize point cloud scan data in a GIS. Tasks that traditionally required expensive surveying equipment and skilled technicians can be achieved with just one smartphone per person, thereby dramatically improving on-site productivity.

LRTK is integrated with cloud services, allowing positioning data and photos to be uploaded to the cloud and shared directly from the field. In fact, LRTK has begun to be used at disaster sites such as earthquakes and heavy rainfall. There are cases in which workers in disaster areas used LRTK-equipped smartphones to measure ground subsidence and structural displacement, and by immediately sharing the photos and point cloud data with stakeholders via the cloud, contributed to rapid situational awareness and response. The ability to enable such real-time information sharing at the field level is also a major strength.

Furthermore, what is particularly noteworthy is that LRTK supports positioning even outside communication coverage. The receiver built into the LRTK supports three-frequency GNSS and can directly receive the aforementioned Japanese CLAS satellite augmentation signal (L6 band). Therefore, even in remote mountains or at sea where cellular signals do not reach, LRTK can obtain correction information from the quasi-zenith satellites overhead and continue RTK positioning. While RTK via NTRIP over networks typically has the weakness of relying on communications infrastructure, LRTK is equipped with functions that complement that weakness. Even in situations where mobile networks are cut off by disasters, positioning and recording become possible, contributing to ensuring reliability in emergencies.

In terms of cost as well, LRTK is priced more affordably than conventional dedicated surveying equipment (※Please check official information for specific prices). With lower initial expenses and the ability to utilize existing smartphones, it has attracted attention for being easy to adopt by small- and medium-sized construction companies, surveying offices, and even at the individual level. It can truly be called a "do-it-all surveying instrument for the field," a solution that advances the democratization of high-precision positioning.

LRTK makes high-precision RTK surveying easier and more accessible. Even those of you who understand how to configure NTRIP on an RTK rover may be able to take your daily surveying and measurement work to the next level by using LRTK. If you're interested, please check out the detailed information on LRTK.

FAQ

Q. What is the difference between RTK and ordinary GPS positioning? A. With standard GPS or GNSS standalone positioning, error factors in satellite signals (such as atmospheric effects and clock errors) cause positional errors on the order of 5-10 m (16.4-32.8 ft). With RTK, a base station calculates these errors in real time and sends correction data to the rover, so the errors can be reduced drastically to the order of a few centimeters (a few in). In short, RTK is a high-precision positioning method that overcomes the weaknesses of standalone positioning by performing relative positioning among multiple receivers.

Q. What information is required for an NTRIP connection? A. To receive correction information via NTRIP, the service provider you subscribe to will provide the following connection information.

• Host name (or IP address): the address of the correction data distribution server

• Port number: the port specified by the server (often 2101)

• Mount point name: the identifier for the data stream to receive

• User ID / password: login information if the service requires authentication Enter these into the NTRIP settings screen of your RTK receiver or positioning app to connect. You can check the information in the documentation or on the website provided at the time of subscription.

Q. Can RTK positioning be performed without preparing a base station? A. Yes — it is possible if you use a network RTK correction service (NTRIP). Even without your own base station, you can receive correction data from a nationwide network of reference stations maintained by the service provider. For example, if you subscribe to a service from a telecom carrier or a surveying-equipment manufacturer, a single rover can perform RTK positioning anywhere in Japan. Note, however, that service fees often apply. As a method that does not use the Internet, you can also receive CLAS from the Quasi-Zenith Satellite System, and with compatible equipment it is possible to achieve accuracy of a few centimeters (cm level accuracy (half-inch accuracy)) without a base station or communications.

Q. Is NTRIP service paid? Are there ways to use it for free? A. Many commercial NTRIP services charge monthly or annual fees. However, because they provide efficiency gains that justify the cost, they are widely adopted in professional settings. On the other hand, there are several ways to try it for free. For example, the Geospatial Information Authority of Japan's electronic reference point data release (experimental) or community-run open NTRIP casters (such as RTK2go provided by volunteers around the world) can be used. However, free services may have unstable connections or no support, so reliability should be considered for business use. Also, the aforementioned CLAS signal is an augmentation service available at no additional cost, so if you have a compatible receiver, using it can reduce communication expenses.

Q. Is an internet connection required to use NTRIP? What should I do when out of coverage? A. Receiving correction data via the NTRIP method basically requires a real-time internet connection. Therefore, normal NTRIP services cannot be used in locations without mobile signal. There are several alternatives for performing RTK positioning when out of coverage. One is using CLAS. With a CLAS-compatible receiver you can receive corrections directly from satellites, allowing high-precision positioning even outside communication coverage. Another is setting up your own base station and sending corrections to the rover via radio (such as low-power radio or LoRa). For example, if you set a control point on site and communicate with local radio, RTK can be achieved without the internet. However, preparing a base station increases the effort involved, so it is generally recommended to use NTRIP when in coverage and to switch to CLAS or local RTK when out of coverage. Solutions that support both, like LRTK, can automatically switch as conditions change and continue receiving corrections, which is convenient.

Q. Is there any way to deal with not being able to obtain a FIX solution? A. First, check the surveying site's environment. If there are many obstructions nearby, satellite signal reception can deteriorate and resolving integer ambiguities (FIX) may take longer. Move to a location with as clear a view as possible or try raising the antenna position. Also, double-check that the NTRIP connection information is correct. In particular, choosing the wrong mountpoint or entering the wrong user ID will prevent you from receiving corrections correctly. If the connection itself is fine, restarting or reconnecting the receiver or software can be effective. Reinitializing RTK can sometimes allow the system to enter FIX smoothly. If you still cannot get a FIX, confirm that your current location is not significantly outside the service area (i.e., outside the provider's coverage area or too far from the reference station). The service provider's support pages and manuals can also be helpful. Finally, if you still cannot resolve the issue, contacting the manufacturer or service provider is another option. Seek advice from experienced personnel while isolating the cause.