Table of contents

• What is RTK?

• How accurate is RTK?

• Centimeter accuracy required in surveying tasks

• RTK applications in construction and civil engineering

• RTK applications in agriculture

• Other use cases (infrastructure inspection, drone surveying, etc.)

• Simple surveying anyone can do with smartphone RTK “LRTK”

• Frequently Asked Questions (FAQ)

What is RTK?

RTK stands for Real Time Kinematic, a positioning technique that corrects GNSS satellite positioning errors, including those from GPS, in real time. With ordinary GPS (standalone positioning), a single receiver receives satellite signals and various error sources remain uncorrected and accumulate, so position errors of several meters (several ft) are common. For displaying your current location on a map with a smartphone GPS, an error of several meters (several ft) is usually acceptable, but in tasks requiring high accuracy such as surveying and civil engineering, errors of several meters (several ft) are unacceptable.

RTK uses two GNSS receivers (a base station and a rover) simultaneously to perform relative positioning and cancel out common errors, yielding highly accurate positions. The base station is a fixed station with known precise coordinates; it calculates the error from the observed satellite data and sends correction information to the rover via radio or the Internet. By applying these corrections, the rover can improve its position to the centimeter level (centimeter level (in)). In short, using two receivers at the same time allows error correction that greatly increases accuracy compared to a single receiver.

Recently, national permanent GNSS networks run by authorities and commercial GNSS correction services (such as VRS distribution by mobile carriers) have been established, so it is now possible to obtain correction data over a network without setting up your own base station. As a result, in the field you often only need to prepare a single GNSS receiver as the rover to perform RTK positioning, greatly lowering the barrier to high-precision positioning.

How accurate is RTK?

With RTK, position determination errors typically fall within a few centimeters (a few in) horizontally and on the order of a few centimeters (a few in) vertically. Field tests have confirmed that under good conditions, positioning errors of about 2–3 cm (0.8–1.2 in) horizontally and about 3–4 cm (1.2–1.6 in) vertically can be achieved. This is an order-of-magnitude improvement over traditional standalone positioning (errors of several meters (several ft)). However, RTK accuracy is still affected by the surrounding environment and satellite geometry. For example, in urban areas with poor sky view (obstruction by tall buildings or multipath environments) or inside forests, a fixed solution may not be obtainable or temporary errors of several tens of centimeters (several tens of in) can occur. Therefore, caution is needed in poor positioning environments, but in open areas centimeter-level accuracy is obtained stably.

For horizontal accuracy, RTK has already reached levels comparable to conventional optical surveying instruments. For example, there are reports of achieving precision under 10 mm (under 1 cm) (10 mm (0.39 in); 1 cm (0.4 in)) by averaging RTK receiver data over a certain period, showing that, for short periods, accuracy comparable to a total station can be obtained. On the other hand, ensuring height (elevation) accuracy may require additional measures, and for applications that demand strict ground elevation determination, combining with other methods such as leveling may be desirable. However, for many tasks such as construction management and topographic surveying, centimeter-level accuracy in both horizontal and vertical directions is sufficient, and RTK has become an indispensable means to meet those requirements.

Centimeter accuracy required in surveying tasks

In land surveying and as-built control, centimeter-level accuracy is often required. Traditionally, it was common to use a total station with two-person teams to set out batter boards (layout marks) or to measure finished dimensions after construction. By introducing RTK-capable surveying equipment, a single person can carry a GNSS rover and measure many points in a short time, dramatically improving surveying productivity. Because coordinate values (projected coordinates or elevations) can be obtained in real time, it is also easy to verify data or perform additional measurements on site, which is a major benefit.

For example, when performing control surveys in public surveying, using network RTK that receives correction data from permanent reference stations allows immediate acquisition of geodetic coordinates (e.g., in the global geodetic system) on site. The resulting survey points with centimeter-level precision (centimeter-level (in)) directly feed into high-precision plan maps and 3D terrain models. During construction, RTK also enables accurate staking out (pile driving or marking). Rather than relying on the intuition of experienced workers, following guidance from a GNSS rover app (e.g., “5 cm east remaining”) allows structural elements to be placed at the specified coordinates. This enables accurate pile driving and layout from the first attempt, preventing rework.

Furthermore, the spread of high-precision GNSS surveying with RTK has created an environment where not only licensed surveyors but also construction managers and workers themselves can perform surveying. Site personnel can measure the height of fill on the spot with a single tablet and immediately reflect it in construction for instant quality control—something RTK makes possible. These are all part of a new on-site style enabled by centimeter-level positioning.

RTK applications in construction and civil engineering

In construction and civil engineering, RTK centimeter accuracy is widely used. On roadworks and earthworks sites, high-precision as-built control is essential to construct according to design dimensions. Traditional surveying errors of tens of centimeters can lead to misalignment or steps in finished structures, but using RTK makes construction at the designed position and elevation possible, directly improving quality.

In ICT-enabled construction, which has become more common recently, GNSS receivers are mounted on construction machinery such as bulldozers and excavators, enabling real-time monitoring of the blade height and position through machine guidance/machine control (MG/MC). Centimeter-level positioning by RTK is essential here. Heavy equipment operators can continuously check the difference between their blade position and the design surface on an in-cab monitor, allowing efficient earthmoving and grading while preventing over-excavation or excess fill. This reduces human error and rework, dramatically improving construction productivity and accuracy.

RTK is also used on construction sites for foundation pile driving and positioning of structures. For example, when installing prefabricated components, workers can use an RTK rover to confirm reference positions and guide placement, enabling installation at nearly millimeter-level accuracy. Also, using RTK to record coordinates of structural elements during post-construction inspection allows immediate detection of deviations from drawings, improving efficiency of inspection tasks. In this way, ensuring “accuracy on the order of several centimeters” is a prerequisite for quality control and efficiency in many construction and civil engineering processes, and RTK is becoming an essential tool on site.

RTK applications in agriculture

RTK centimeter accuracy also brings great value in agriculture. Particularly in the emerging field of smart farming, RTK-equipped auto-steer tractors are becoming widespread. A GNSS antenna mounted on the tractor provides high-precision positioning, and automatic steering allows straight and accurate passes across large fields without human intervention. With guidance allowing straight lines within about 2–3 cm (0.8–1.2 in) error, uniform seeding and fertilization that were difficult even for experienced operators can be achieved by anyone.

RTK guidance minimizes overlaps and skips between adjacent swaths, reducing wasted double application and shortening working time. For example, reports indicate that introducing RTK auto-steer tractors can reduce labor time by about 9% compared with conventional methods. Precise row tracking also reduces the risk of unnecessarily trampling crops, preventing yield loss (one demonstration showed average yield increases of about 9%). In precision agriculture, the positioning accuracy provided by RTK offers benefits across the board: reduced input costs, increased yields, and safe automated operation.

Additionally, in agriculture there is progress in analyzing collected high-precision trajectories to improve farm management. By accumulating and visualizing RTK-acquired operation tracks, operators can grasp detailed in-field work situations and feed that back into future work plans. With centimeter-level position information (centimeter-level (in)) available even over vast fields, data-driven farming that does not rely solely on intuition or experience is becoming possible. RTK adoption strongly supports automation and labor saving in agriculture, and as smart farm machinery becomes more widespread, farming operations will become dramatically more efficient.

Other use cases (infrastructure inspection, drone surveying, etc.)

Centimeter-level positioning has produced new solutions outside surveying, construction, and agriculture. For example, in infrastructure maintenance, attaching high-precision location information to photos and sensor data from regular inspections of tunnels and bridges makes it easy to record exact deterioration locations and monitor changes over time. Marking the positions of buried utilities detected by ground-penetrating radar with RTK reduces the risk of damaging pipes during excavation. RTK is also applied to safety management of work vehicles. In railway maintenance, equipping work vehicles with RTK receivers and matching their positions in real time with train suspension zones can prevent entry accidents caused by human error.

RTK also plays a crucial role in the now-popular field of drone-based surveying and inspection. Using RTK-capable drones, orthomosaic maps and 3D point cloud models generated from aerial photos can have position errors reduced to a few centimeters (a few in). Traditionally, many ground control points (targets) had to be placed during drone surveys to correct positions, but RTK drones require far fewer control points, greatly streamlining the workflow. The high-precision maps and point clouds obtained are powerful tools for road and river maintenance, disaster damage mapping, and more. Accelerated digital twin initiatives on sites improve the reliability of planning and preventive maintenance.

Simple surveying anyone can do with smartphone RTK “LRTK”

Although RTK positioning is high-precision and convenient, it traditionally required dedicated expensive GNSS equipment and skilled operators. Now, however, the era is coming where anyone can easily achieve centimeter-level positioning using a smartphone. A representative example is the solution called LRTK. LRTK is a compact RTK-GNSS receiver that integrates with a smartphone; by attaching it to an iPhone or iPad it turns the device into a pocket-sized “all-purpose surveying instrument.” By attaching a device weighing only about 125 g to a smartphone and launching a dedicated app, network RTK or Japan’s quasi-zenith satellite system Michibiki (CLAS) can be used to obtain centimeter-level positioning immediately.

Using LRTK greatly simplifies surveying and staking out. For example, at the point you want to measure, you simply press a button on the smartphone screen to record the point’s latitude, longitude, and height. Recorded points are automatically saved to the cloud, and survey point data can be checked in real time from the office. The app automatically handles conversions to projected coordinate systems and geoid height calculations, so accurate coordinates can be obtained without specialized knowledge. LRTK supports not only point measurements but also continuous positioning—by recording up to 10 track points per second while walking, you can measure terrain cross-sections, for example.

LRTK is also useful for on-site staking and layout. With a GNSS guidance app, the smartphone guides you on how far you are from the specified coordinates, enabling accurate alignment without complex equipment operation. In combination with the smartphone camera, AR features can overlay design positions onto the real-world view, helping intuitively locate buried utilities or design lines and improving on-site safety.

RTK equipment that once required investments on the order of millions of yen can be introduced at astonishingly affordable prices with LRTK. It is compact and inexpensive enough for one person to carry one unit on site, so non-specialists can take measurements as needed. Companies that have introduced LRTK on site report that tasks they previously requested from surveying teams can now be done in-house, dramatically increasing productivity. The latest smartphone RTK devices like LRTK are opening a new era in which anyone can easily handle centimeter-level positioning.

Frequently Asked Questions (FAQ)

Q: Is RTK accuracy really on the order of a few centimeters? A: Yes. RTK positioning typically yields horizontal errors of about 2–3 cm (0.8–1.2 in) and vertical errors of about 3–5 cm (1.2–2.0 in). In ideal environments (open sky) even sub-centimeter accuracy can be obtained. However, in environments with tall buildings or inside forests where visibility is poor, accuracy can temporarily degrade and errors exceeding 10 cm (several in) may occur. To obtain stable centimeter-level accuracy, it is desirable to perform GNSS positioning in areas with as clear a view of the sky as possible.

Q: What is required to perform RTK positioning? A: Basically, RTK requires an RTK-capable GNSS receiver as the rover and a base station (or correction service) that provides correction data. A single GPS receiver alone is insufficient to achieve centimeter accuracy; you need to set up a base station with known coordinates nearby or obtain base station data over a network. In Japan, correction data can be obtained from permanent reference stations or paid services provided by mobile carriers. A communication link (radio modem or Internet connection) between the rover and the base station is also required. Recently, Internet services distributing correction data have become widespread, and with an Ntrip-compatible receiver you can start RTK positioning without special equipment.

Q: Can you do RTK surveying with a smartphone? A: Yes. Standalone smartphone GPS is coarse with errors of several meters (several ft), but by connecting an external RTK receiver to the smartphone, centimeter-level positioning is possible. For example, using a small iPhone-compatible device like LRTK turns a smartphone into a high-precision GNSS surveying instrument. By receiving correction data while positioning with a dedicated app, point surveying and staking out can be performed with accuracy comparable to professional surveying instruments. Since current position and surveyed coordinates can be checked in real time on the smartphone screen, even beginners can operate intuitively. Smartphone-based RTK surveying is already practical and is attracting attention as a lower-cost, easier-to-use alternative to traditional equipment.

Q: What factors affect RTK positioning accuracy? A: Major factors include the satellite signal reception environment and the quality of correction information. High accuracy is obtained when the sky view is open and many satellites can be observed, whereas in forests or urban canyons satellites may be blocked or signals reflected (multipath), increasing errors. Also, the further you are from the base station, the less effective atmospheric error correction becomes; generally, accuracy stabilizes when the distance to the base station is within a few km. Network RTK can maintain accuracy over wider areas using virtual reference stations (VRS), but satellite geometry (GDOP) and radio interference still have effects. When using mobile communications, delays or disconnections can interrupt correction data and degrade accuracy. Therefore, when operating RTK, it is important to ensure as clear a sky view as possible and a stable environment for receiving correction data.