What Is RTK GPS? Centimeter‑Level Surveying Explained | LRTK

Table of Contents

• What is RTK GPS?

• Centimeter-level positioning accuracy achievable with RTK GPS

• How RTK GPS works: corrections from a base station and rover

• Fields where RTK GPS is active and its benefits

• Challenges of introducing RTK surveying

• Simple surveying with LRTK

• FAQ

What is RTK GPS?

RTK GPS is a surveying technique that uses satellite positioning systems (GNSS) to obtain highly accurate position information in real time. "RTK" stands for *Real Time Kinematic*, and it calculates the rover’s position at centimeter-level accuracy by sending correction data from a base station to the rover. Conventional GPS (standalone positioning) can have errors of several meters, but using RTK GPS can reduce those errors to a few centimeters. Because this high-precision positioning can be achieved easily on site, the adoption of RTK GPS has rapidly expanded in recent years in construction, civil engineering, and surveying.

Centimeter-level positioning accuracy achievable with RTK GPS

The GPS (GNSS) in common smartphones or car navigation systems is convenient because it determines position using a single receiver, but it inevitably produces errors of several meters. Such meter-level deviations are acceptable for showing your current location in a map app, but for accurately laying out positions in construction or detecting minute displacements in infrastructure inspection, centimeter-level accuracy is required. Using RTK GPS enables this kind of high-precision, "centimeter-level positioning."

So what is the difference between standalone positioning and RTK positioning? The biggest difference is the presence or absence of error correction. RTK receives correction information from a base station in real time and applies it to the rover’s positioning results, greatly reducing errors. A summary comparison is below.

• Standalone positioning (normal GPS): A single receiver determines position from satellites. Without corrections, position errors can be on the order of several m.

• RTK positioning: Uses two receivers, a base station and a rover. By applying correction information calculated at the base station to the rover, errors can be reduced to the order of several cm.

Because RTK GPS provides orders-of-magnitude higher accuracy, it is becoming an indispensable technology in surveying and construction management.

How RTK GPS works: corrections from a base station and rover

The key to RTK’s high accuracy is the combination of a base station (fixed station) and a rover (mobile station). A base station is a GNSS receiver installed at a point whose precise coordinates (latitude and longitude) are known. The rover is a receiver carried to the measurement point. When the base station and rover receive signals from the same satellite at the same time, their raw data contain common error factors (such as atmospheric delays and satellite clock offsets). The base station calculates the instantaneous positioning error from the difference between its known precise position and the satellite-derived position. It then sends that error information to the rover via radio or the Internet, and the rover applies the correction to its own positioning result to obtain high-accuracy coordinates.

Because this correction is performed in real time every second, the rover can measure its position to centimeter accuracy even while moving (hence the term real-time kinematic). Also, the closer the base station and rover are, the more similar their common error factors, so the correction is more effective. In general, within several km the positioning error can be maintained at a few centimeters.

Recently, it has become possible to perform RTK positioning without setting up your own base station by obtaining correction data over the Internet from public continuously operating reference stations or private GNSS reference station networks deployed nationwide. For example, if you subscribe to a network RTK service that uses the cellular network (VRS method, etc.), you can easily achieve centimeter-level positioning with only a rover. In Japan, the Geospatial Information Authority’s network of reference stations and correction services provided by telecommunications companies are well developed, making high-precision positioning possible on site without installing your own base station.

Fields where RTK GPS is active and its benefits

Centimeter-accuracy position information from RTK GPS is used across many fields. Below are major use cases and the benefits that improved accuracy brings.

• Construction and civil engineering site management: In roadworks, bridge construction, and similar projects, RTK positioning enables accurate layout (marking and stake-driving) according to design drawings. Because initial work is less prone to deviation, the quality of the finished work improves. In ICT construction (smart construction) promoted by the Ministry of Land, Infrastructure, Transport and Tourism, machine guidance/machine control with GNSS-equipped heavy machinery is used, and that high-precision position control is supported by RTK-GNSS. Operators can continuously check the blade’s current elevation against the design surface on a monitor, enabling efficient construction without over-excavation or under-excavation. This can reduce rework and improve work efficiency.

• Survey work efficiency: RTK is revolutionary in civil surveying. Traditionally, as-built surveys and setting out required total stations with two-person teams. With RTK-capable GNSS receivers, a single person carrying a rover can walk the site and measure many points in a short time. Because planar rectangular coordinates and elevations are obtained in real time, data can be checked and additional measurements made on the spot. This contributes significantly to reduced personnel and shorter work times, preventing project delays caused by waiting for surveying.

• Infrastructure inspection and maintenance: High-precision position records are useful in regular inspections of tunnels, bridges, roads, and other infrastructure. For example, when monitoring bridge pier settlement annually, RTK’s centimeter accuracy can detect very small displacements. If inspection points are registered, the same location can be revisited with RTK later, enabling accurate tracking of changes. Improved reliability of position information directly supports safety and security in infrastructure maintenance.

• Disaster survey and recovery: RTK positioning is also powerful in disaster response such as landslides and earthquakes. Using an RTK-equipped drone for aerial photography allows rapid creation of precise topographic maps via photogrammetry. Even in hazardous areas where people cannot enter, centimeter-accurate maps from the air enable quick situational assessment and recovery planning. In post-disaster infrastructure inspections, RTK is effective for accurately locating and recording damaged areas.

As shown above, RTK GPS provides benefits such as improved accuracy (quality assurance) and efficiency (time and labor savings), which is why adoption is progressing mainly in the construction and surveying industries. The ability to obtain high-precision positioning data in real time strongly supports on-site DX (digital transformation).

Challenges of introducing RTK surveying

Although RTK positioning is very useful, its introduction traditionally faced several hurdles. The first was the bulkiness of equipment. RTK required bringing high-performance GNSS receivers plus base station antennas, batteries, and radio modems to the site, connecting them with cables and setting them up. Initial system costs could be high, and operation often assumed professional surveyors. For small businesses or technicians inexperienced in surveying, the perception that RTK was "complicated" or "too expensive" led to hesitation in adopting it.

In addition, securing communications for RTK positioning is essential. When using your own base station, operations must be conducted within radio range between the base and rover, so communication can be challenging in mountainous areas or locations with poor line of sight. With network-based methods like VRS using cellular networks, movement is freer within coverage areas, but positioning is difficult outside coverage. Thus, selecting equipment configuration and communication methods according to operational conditions added to the operational complexity.

However, in recent years, user-friendly and low-cost RTK solutions that overturn these conventional assumptions have appeared. One such solution is the LRTK series, introduced next.

Simple surveying with LRTK

The LRTK series is an all-in-one RTK positioning device developed to solve the challenges described above. Developed by Lefixea, LRTK integrates all the equipment needed for RTK positioning (antenna, GNSS receiver, battery, communication module) into a single unit, achieving a completely wireless, compact, and lightweight GNSS terminal. It is ruggedly designed for dust and water resistance for on-site use, so it can be used safely in rainy or dusty construction environments.

There are several models of LRTK devices for different uses, but the standout is the pocket-sized LRTK Phone. This smartphone-integrated RTK receiver uses a dedicated ultra-compact GNSS module (weight approximately 125 g; thickness 13 mm (0.51 in)) that you attach to an iPhone or Android device, turning your smartphone into a versatile surveying instrument capable of centimeter-level positioning. It overturns the image of traditional RTK equipment with a truly compact design, developed to be literally "pocketable and ready to use when needed."

With LRTK, all you need is your smartphone. No complicated wiring or dedicated controller is required, and the built-in battery enables about 13 hours of continuous positioning, sufficient for a day’s work. It supports Bluetooth and Wi‑Fi connectivity and pairs with smartphones using standard protocols (NMEA output). With the dedicated "LRTK app," positioning and recording can be started with a single tap, making operation intuitive for anyone. Notably, LRTK supports Japan’s QZSS-provided centimeter-level positioning augmentation service (CLAS). While ordinary network RTK requires a cellular connection, LRTK can receive augmentation signals directly from satellites, enabling high-precision positioning even in remote mountain areas or islands outside cellular coverage (by switching the antenna to CLAS reception mode). It can also switch to cellular-network-based VRS with one touch, allowing selection of the optimal positioning method according to site conditions. This flexibility is powerful in scenarios where GNSS positioning is difficult, such as inside tunnels or forests.

LRTK includes not only hardware but also rich software and cloud services. The LRTK app automatically converts measured points to Japan’s plane rectangular coordinates, and can instantly calculate distances, areas, and volumes of multiple points on site. For example, the positioned photo feature automatically tags high-precision coordinates and orientation information to photos taken with your smartphone. Shared via the cloud, office staff can accurately know "which point and which direction the photo was taken from." The point cloud scan feature acquires 3D point clouds on site by linking with the smartphone’s camera or LiDAR scanner and saves them as survey data. You can immediately calculate earthwork volumes (fill/excavation) or draw arbitrary cross-sections. The coordinate guidance feature navigates a worker toward pre-registered coordinates with AR display. Even reference points or stakes whose exact locations are unknown on site can be pinpointed with LRTK. All these functions are completed with a smartphone + one LRTK device, making it an indispensable digital tool on site.

Thus, LRTK is a next-generation RTK solution that enables "anyone, anywhere, easily" to utilize centimeter-level positioning. By turning what used to require specialists and expensive dedicated equipment into a smartphone-like experience usable by anyone on site, LRTK promises dramatic productivity improvements. In fact, one construction site reported that after introducing LRTK, waiting times for outsourced surveying drastically decreased and site managers themselves were able to perform surveys and as-built confirmations. By greatly lowering the barrier to incorporating centimeter-level accuracy into daily operations, LRTK can be seen as a new evolution of RTK technology.

The LRTK series dramatically improves on-site surveying accuracy and work efficiency. It brings high-precision GNSS positioning closer to the construction, civil engineering, and surveying sectors and is an optimal solution compatible with the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction initiative.

For more details, please see the links below.

• [LRTK Official Site](https://www.lefixea.com/)

• [LRTK Series | Device List Page](https://www.lefixea.com/)

• [Case Study | Use cases on construction sites](https://ken-it.world/success/2024/09/lrtk-phone-boom.html)

For product inquiries or demo requests, please feel free to contact us via the [inquiry form](https://www.lefixea.com/contact-lrtk). We hope you will apply LRTK’s high-precision positioning on your sites and evolve to the next stage.

FAQ

Q: What is the difference between RTK GPS and normal GPS? A: Normal GPS positioning uses a single receiver to receive satellite signals, which is convenient but produces significant errors on the order of several meters. RTK GPS uses correction data from a base station to cancel positioning errors in real time, yielding orders-of-magnitude higher accuracy of within a few centimeters.

Q: How accurate is RTK positioning? A: It depends on conditions, but generally RTK achieves horizontal accuracy of about ±1–3 cm (±0.4–1.2 in) and vertical accuracy of about ±3–5 cm (±1.2–2.0 in). In good conditions with a high-quality receiver, even higher accuracy (less than 1 cm (<0.4 in)) can be achieved. However, accuracy may decrease in areas with poor satellite reception, such as forests or high-rise urban areas.

Q: What equipment is needed to start RTK positioning? A: Basically, you need a GNSS receiver for the base station and a GNSS receiver for the rover, plus a communication method connecting the two. The base station must be at a point with known precise coordinates. Communication is done via dedicated radios (such as UHF data links) or over the Internet (Ntrip using cellular connections). Recently, there are more cases where you can obtain correction information from national or private reference station networks, so you may be able to position with just a rover receiver and a communication terminal. Solutions like LRTK that integrate required equipment let you start RTK positioning easily with only a smartphone and a receiver.

Q: How far from the base station can you position? A: The closer the base and rover are, the higher the accuracy. As a general guideline, within several km the RTK error is typically on the order of a few centimeters. However, as distance increases, atmospheric errors grow, so if the base is 20–30 km (65,616.8–98,425.2 ft) away, corrected errors may expand to several tens of centimeters. To address this, network RTK with multiple base stations generates a virtual reference station (VRS) near the user so that uniform cm level accuracy (half-inch accuracy) can be obtained over wide areas. Using nationwide reference station networks and correction services, depending on the region, you can achieve practically usable accuracy even when tens to hundreds of km away.

Q: Is RTK positioning possible outside cellular coverage? A: With VRS that uses cellular networks, positioning is normally difficult outside coverage because correction data cannot be received. There are countermeasures: one is the traditional method of direct communication between a base and rover using specific low-power radio (with limited range). Another is to use satellite-based augmentation like QZSS’s CLAS. A CLAS-compatible receiver can receive corrections directly from satellites and perform RTK positioning in mountainous areas. LRTK supports CLAS, enabling centimeter-level positioning even at sites without cellular coverage.

Q: How much does it cost to introduce RTK GPS? A: The cost of RTK surveying equipment varies by configuration. Traditional professional GNSS receivers could cost several million yen for a base and rover set, with additional fees for high-precision correction services. New products like LRTK have significantly reduced costs, lowering the barrier for initial investment. Specific prices depend on equipment configuration and scale, so please contact us for a detailed proposal.

Q: How should I choose between a total station and RTK positioning? A: A total station (TS) achieves millimeter-level precision by line-of-sight distance measurement to prisms and is suitable for vertical building layout and indoor dimensioning. However, TS measurements require line-of-sight and sometimes multiple people and setup of reference points. RTK positioning can obtain absolute coordinates over wide areas with satellite visibility and allows a single person to quickly measure many points. But RTK cannot be used where radio signals are unavailable (indoors or in dense forests). Therefore, it is ideal to use both complementarily on site. For example, use RTK to efficiently measure reference coordinates across the site, and use a total station for detailed measurements or points where GNSS cannot reach. One does not render the other unnecessary; use each according to site conditions to leverage their strengths.