Table of Contents

• What is RTK? Background on why centimeter-level accuracy is attracting attention

• Conditions required to achieve centimeter accuracy with RTK positioning

• Common misconceptions about RTK accuracy and the truth behind them

• Latest trends in simplified RTK surveying: high-precision positioning with LRTK

• FAQ

What is RTK? Background on why centimeter-level accuracy is attracting attention

In recent years, on-site needs in construction, civil engineering, and surveying have grown for positioning with the smallest possible errors. Conventional GPS positioning (GNSS standalone positioning) is convenient, but its errors are commonly on the order of meters. A few meters of error is fine for checking your current position on a mapping app, but centimeter-level accuracy is required for tasks such as positioning structures at construction sites or detecting slight displacements in infrastructure inspections.

RTK positioning (Real Time Kinematic) is a high-precision positioning technology attracting attention for this reason. RTK uses two GNSS receivers — a base station and a rover — to perform real-time relative positioning, canceling various errors present in satellite positioning and enabling accuracy that standalone positioning cannot achieve. With RTK, under the right conditions, position errors can be reduced to a few centimeters horizontally and a few centimeters vertically. In other words, the GPS positioning error that normally shifts by about 5–10 m (16.4–32.8 ft) can be reduced by roughly a factor of 100 with RTK.

This centimeter-level accuracy is critically important for initiatives like construction DX (i-Construction) being promoted in Japan. In roadworks or bridge construction, large surveying errors can lead to misplacement of constructed structures or errors in elevation. By using RTK, you can perform highly accurate layout and as-built measurements according to the design drawings, enabling high-quality construction. In drone surveying and equipment monitoring, centimeter-level position data dramatically increases data reliability. As a result, RTK technology is being adopted across a wide range of sites, from major general contractors to small and medium construction firms, surveying companies, and infrastructure maintenance personnel.

Conditions required to achieve centimeter accuracy with RTK positioning

To achieve “errors of a few centimeters” with RTK, several conditions must be met. RTK is indeed a powerful technology, but it is not the case that “using it automatically yields 1 cm accuracy”; appropriate environments and procedures are required to realize that accuracy. Let’s look at the main points in order.

• Base station correction data: RTK requires a base station installed at a known, accurate position. The base station calculates the error components from the satellite signals it receives and transmits those corrections to the rover. Thanks to this correction information, the rover (the point to be measured) can cancel errors it could not correct on its own and compute a high-precision position. Nowadays, it is possible to obtain correction information without setting up your own base station by using public Continuously Operating Reference Stations (CORS) or commercial correction services (network RTK using mobile networks). In all cases, the prerequisite for centimeter accuracy is that you can receive accurate correction data in real time.

• Distance to the base station: The closer the base station (or virtual reference point) is to the rover, the more similar the error factors affecting both (such as atmospheric signal delays and satellite orbit errors) will be, resulting in higher accuracy. Generally, if the rover is within a few kilometers of the base station, RTK is likely to maintain centimeter-level accuracy. Conversely, as distance increases, uncorrectable errors grow and positioning accuracy gradually degrades (as a rough guideline, error increases by a few millimeters for each additional 1 km). For high-precision surveying, it is effective to place a base station near the survey area or use network RTK based on CORS distributed nationwide.

• Satellite observation environment: To achieve centimeter accuracy with RTK, it is important to be in an environment where GNSS signals from satellites can be received stably. In open areas with a clear view of the sky and a sufficient number of visible satellites, dense observation data can be obtained and RTK solutions — especially the high-precision “fixed solution” — are stably achievable. By contrast, in urban canyons or forests where tall obstructions surround you, or during times when satellite geometry is poor, the number of receivable satellites may decrease and RTK accuracy will be affected. In particular, multipath environments, where satellite signals are reflected by buildings or terrain, increase errors and make it difficult to obtain an accurate solution. To achieve centimeter accuracy, measures such as surveying in as-open-a-location-as-possible or choosing times with fewer obstructions are necessary.

• GNSS receiver and frequency bands: The performance of the GNSS receiver used in RTK positioning also affects accuracy. For high precision, a receiver capable of tracking carrier-phase signals (the phase of the radio wave) is required, allowing handling of raw data with millimeter-level precision. Receivers that support multi-GNSS and multi-frequency are advantageous. Being able to use multiple satellite constellations (not only GPS but also GLONASS, Galileo, and Michibiki (QZSS)) increases the number of visible satellites and improves positioning stability. Using multiple frequency bands such as L1/L2 also helps remove ionospheric errors and shortens the time to achieve the fixed solution. Recently, inexpensive multi-band RTK-GNSS modules have appeared, making high-precision positioning more accessible than before.

If these conditions are met, RTK can provide astonishing accuracy within a few centimeters horizontally and vertically. However, these are essentially “ideal conditions,” and in real surveying situations, accuracy can fluctuate depending on the environment and operation. The next section explains common misconceptions about RTK accuracy and the truth behind them.

Common misconceptions about RTK accuracy and the truth behind them

RTK is an excellent technology capable of centimeter-level accuracy, but misunderstanding its mechanisms and conditions can lead to incorrect expectations and operational mistakes. Here we address common misconceptions often seen in RTK articles or promotions and clarify the correct understanding.

Misconception 1: “If you use RTK, you will always be within 1 cm error”

Some people assume that installing RTK will always yield sub-centimeter errors. In reality, RTK accuracy is also influenced by surrounding environmental conditions. As noted earlier, if satellite reception conditions are poor, RTK may fail to obtain a fixed solution and temporary errors of about 10 cm can occur. In particular, in urban areas surrounded by high-rise buildings or in densely wooded mountain regions, while average horizontal and vertical precision may be a few centimeters, there have been verified cases where deviations exceeded 10 cm. Therefore, instead of believing “RTK = always 1 cm accuracy,” it is important to properly understand that RTK is “a technology that achieves a few centimeters in good environments and at worst tens of centimeters.” In other words, RTK is a means to greatly reduce errors, but in real environments there are limits to achievable accuracy.

Misconception 2: “If centimeter accuracy is achieved, the absolute position is also accurate”

The phrase “centimeter-level accuracy” can be interpreted to mean “the measured coordinates themselves are only a few centimeters off in a global coordinate system,” but caution is required. RTK coordinates primarily indicate centimeter-level relative accuracy to the base station, and this assumes the base station’s position is accurately known. If the base station’s coordinates are erroneous or offset, the coordinates measured by the rover will be shifted by the same amount. For example, if you use a casually installed base station that is actually off by several meters, RTK surveying will yield high relative accuracy within the site, but overlaying the obtained coordinates on a public map could show shifts of several meters. Understand that “centimeter accuracy” does not necessarily equal “absolute accuracy”; it means high relative accuracy tied to the reference point.

Regarding this point, using the Geospatial Information Authority of Japan’s CORS network for network RTK or correction services provided by mobile carriers is reassuring. These base station networks are rigorously calibrated to public coordinate systems, so positioning results obtained have high absolute accuracy in public geodetic frameworks. On the other hand, when conducting RTK with a temporary local base station on site, you should calibrate it to known control points in advance or perform coordinate transformation in post-processing.

Misconception 3: “RTK surveying requires expensive, specialized equipment”

Some may believe RTK requires specialized surveying gear and that costs are prohibitively high. Indeed, RTK-GNSS receivers used to cost several million yen and require specialist knowledge. However, advances in technology and widespread adoption have made RTK equipment smaller and more affordable. For example, pocket-sized GNSS receivers and devices that work with smartphones to achieve centimeter-level positioning are appearing. This is making high-precision positioning, once limited to professional surveyors, more accessible to a wider range of users.

Also, the spread of network RTK means you often don’t need to carry expensive radios or base stations for each site. Correction information can be received via a smartphone’s mobile network, so only the rover receiver is required. Additionally, Japan’s Quasi-Zenith Satellite System “Michibiki” offers CLAS (Centimeter-Level Augmentation Service), which allows acquisition of augmentation signals directly from satellites so high-precision positioning is possible even in mountainous areas without internet connectivity. In short, modern RTK surveying is not necessarily large-scale; it can be achieved with relatively simple setups.

Misconception 4: “If you have the latest smartphone, you can get centimeter accuracy by itself”

High-performance GPS chips are now built into smartphones, and some advertise “multi-frequency support” and “positioning augmentation support.” You might therefore think that the latest smartphones alone can produce centimeter accuracy without dedicated GNSS equipment. However, at present, achieving RTK-level 1–2 cm accuracy with a smartphone alone is extremely difficult. One reason is antenna performance: the small antenna inside a smartphone introduces significant noise in positioning signals, making it hard to obtain a stable fixed solution. Also, the augmentation information accessible to smartphones is limited, so standalone smartphone positioning usually improves accuracy only to the order of tens of centimeters (the range of SBAS or multi-frequency standalone positioning). To obtain centimeter-level accuracy in real time, a dedicated RTK-capable receiver and appropriate correction information are still necessary.

That said, lightweight RTK devices designed to work with smartphones have emerged. By combining a smartphone’s display and communications with a high-performance GNSS receiver, it is now possible to achieve accuracies comparable to traditional stationary equipment. A representative example is the LRTK series of devices.

Latest trends in simplified RTK surveying: high-precision positioning with LRTK

The barriers to leveraging RTK’s centimeter accuracy are steadily lowering, and at the forefront of this trend is a solution called LRTK. LRTK is an ultra-compact RTK-GNSS receiver series developed by Refixia Co., and when used with a smartphone or tablet, it realizes a “palm-sized surveying instrument.”

For example, the “LRTK Phone” weighs only about 165 g and, despite a thickness of approximately 1 cm (0.4 in), supports GPS, GLONASS, Galileo, Michibiki, and other multi-GNSS, and even offers 3-band support (L1/L2/L5). By attaching this device to an iPhone or iPad and launching the dedicated LRTK app, the smartphone instantly becomes a centimeter-precision surveying instrument.

LRTK’s strengths are not only hardware. It is designed for ease of use: positioning data is transferred to the smartphone in real time via Bluetooth. Field-acquired position data can be uploaded to the “LRTK Cloud” with a single tap, enabling immediate data sharing with office staff. This allows remote verification of the latest survey results, cloud-based measurement of distances and areas between points, and other collaborative tasks to be performed seamlessly.

Moreover, LRTK supports not only network RTK but also Japan’s satellite augmentation service Michibiki (QZSS) CLAS. Therefore, even in mountainous areas without mobile coverage, LRTK can obtain high-precision correction information directly from satellites and maintain centimeter-level positioning. This overturns the conventional wisdom that “high-precision positioning equals dependence on communications,” enabling stable RTK surveying anywhere.

By using LRTK, one person can easily achieve centimeter-level positioning. There is no need to carry heavy tripods and stationary receivers; surveying can be completed with just a smartphone and a pocket-sized device. Acquired data automatically includes coordinates such as latitude, longitude, and elevation, making comparison with design drawings and maps smooth. Because position results can be managed together with photos, notes, and point-cloud data on the smartphone or in the cloud, report creation and handover to downstream processes are also streamlined.

By correctly understanding the conditions and mechanisms of RTK and adopting such cutting-edge tools, an era is approaching in which anyone can enjoy centimeter-level positioning on site. Why not experience next-generation simplified surveying with LRTK and maximize RTK’s potential?

FAQ

Q. Can RTK really achieve about 1 cm accuracy? A. Yes — under the right conditions, high-precision positioning with horizontal/planimetric errors of about 1–3 cm (0.4–1.2 in) and vertical errors of about 3–6 cm (1.2–2.4 in) is possible. However, this applies to open environments with good satellite visibility. In urban canyons or forests, temporary errors exceeding 10 cm can occur. The important point is that RTK is far more accurate than ordinary GPS, but you should understand that some error can still occur depending on the environment.

Q. Can RTK positioning be done without preparing a base station? A. Yes. Throughout Japan, the Geospatial Information Authority of Japan’s CORS are installed and network RTK services (such as VRS) based on them are available. If the rover receiver can receive correction information via the internet, RTK positioning is possible without installing a dedicated base station. In Japan, Michibiki’s CLAS signal is also available, allowing direct satellite-based corrections for centimeter accuracy in areas far from base stations.

Q. What is the difference between RTK and DGPS (Differential GPS)? A. DGPS also receives corrections from a base station, similar to RTK, but differs in accuracy and method. DGPS mainly corrects code-based positioning errors, so its accuracy is typically several tens of centimeters to about 1 m. RTK uses carrier-phase measurements and can reduce errors to a few centimeters. RTK achieves stable high precision by obtaining a fixed solution, whereas DGPS only suppresses slowly drifting errors, so RTK is superior for long-term stable positioning.

Q. Can you use LRTK without surveying experience? A. Yes. LRTK is designed to minimize technical operations; connect it to your smartphone, launch the app, and follow the guidance to start positioning. Basic operations like observing and saving points are intuitive with button taps, and acquired data is automatically plotted on a map. You do not need to handle complicated settings or positioning calculations like traditional surveying instruments. However, understanding RTK principles and precautions (such as the importance of clear satellite visibility) will help you achieve reliable high precision.

Q. Compared to conventional high-precision GNSS equipment, what advantages does LRTK offer? A. The biggest advantages are portability and ease of use. LRTK fits in a pocket, greatly reducing the burden of transporting equipment on site. Its smartphone integration enables real-time cloud sharing and data management. In terms of accuracy, experiments have confirmed positioning within error ranges from a few millimeters to a few centimeters, comparable to GNSS receivers that used to cost millions of yen. Additionally, CLAS reception from Michibiki allows continued positioning even outside mobile network coverage, making LRTK powerful for surveying in remote mountainous areas. Overall, LRTK offers a new surveying style: “high-precision comparable to high-end equipment, with smartphone-like usability.”