RTK GNSS Introduction Guide: Basic Steps to Start High-Precision Surveying

In recent years, there has been an increasing need for centimeter-level (cm-level accuracy, half-inch accuracy) high-precision surveying on construction and surveying sites. The technology attracting attention to support this is RTK GNSS. This article explains, in an easy-to-understand way, the basics of what RTK GNSS is and the steps and key points to introduce high-precision surveying. It is written so that even those handling RTK GNSS for the first time can understand, so please use it as a reference.

Table of Contents

• What is GNSS?

• What is RTK?

• Advantages of high-precision surveying with RTK GNSS

• What you need to start RTK GNSS surveying

• Basic steps for RTK GNSS surveying

• Points and precautions for introducing RTK GNSS

• Simple surveying with LRTK

• FAQ

What is GNSS?

First, GNSS stands for Global Navigation Satellite System and is a general term for global navigation satellite systems that use artificial satellites to determine positions on Earth. GPS, well known to many, is one of these and is the satellite positioning system operated by the United States. Other countries also have their own GNSS satellite constellations, such as Russia’s GLONASS, Europe’s Galileo, and Japan’s Quasi-Zenith Satellite System (QZSS; Michibiki). A GNSS receiver (positioning terminal) receives radio signals from multiple satellites overhead and calculates its current position (latitude, longitude, altitude) from information such as signal propagation times.

Common GPS receivers built into smartphones or car navigation systems can determine approximate positions. However, ordinary GNSS positioning inevitably has errors on the order of several meters due to various factors such as atmospheric signal delays and satellite clock errors. A few meters of error is acceptable for daily navigation, but is insufficient for layout work on construction sites or fine surveying. That is where the high-precision positioning technique called the RTK method, explained next, comes in.

What is RTK?

RTK (Real-Time Kinematic) is a positioning method that applies real-time corrections to GNSS positioning errors to achieve centimeter-level accuracy. RTK positioning typically uses two GNSS receivers: a base station and a rover. First, the base station is installed at a known coordinate point (a known control point) and the satellite signal data received at that location are transmitted in real time via radio or the Internet. The rover receives that correction data and applies it to its own measured position information to determine a highly accurate current coordinate. Simply put, the mechanism is that the stationary receiver (base station) measures error information and tells the moving receiver (rover) that information, dramatically improving the rover’s positioning accuracy.

Applying RTK corrections reduces GNSS position errors that were previously several meters down to within a few centimeters. For example, under good satellite signal conditions within a few kilometers (a few mi) of the base station, planar positions of about ±1–2 cm (±0.4–0.8 in) and vertical accuracy of about ±2–3 cm (±0.8–1.2 in) can be obtained. This accuracy is comparable to conventional surveying instruments and is sufficient for tasks such as control point surveys and structure placement. As the name implies, RTK positioning is performed in real time, so the rover operator can immediately confirm the current position and record survey points or stake out design positions on the spot.

There are methods of RTK corrections where you set up your own base station on site and transmit correction information by radio, and there is a network RTK method that receives correction information from public reference station networks via the Internet. Using the latter (network RTK) means you don’t have to physically install a base station on site and can start RTK positioning as long as cellular data is available. In either method, when the rover receives correction data and corrections are properly applied, high-precision positioning is established (some models display this state as a “FIX solution” or “fixed solution”). FIX means that ambiguities have been resolved and the position solution is stable; only in this state can centimeter-level positioning data be obtained.

Advantages of high-precision surveying with RTK GNSS

Introducing RTK GNSS provides various advantages over conventional surveying methods. Here are the main benefits of using RTK GNSS for high-precision surveying.

• Significant increase in work efficiency: Using RTK GNSS allows rapid measurement of many points. For example, conventional surveying with a total station could take more than half a day to stake out 100 points, but with RTK this can be completed quickly. Because coordinates are obtained in real time, you can proceed while instantly confirming whether a location matches the design on the spot.

• Reduced personnel (one-person operation): GNSS surveying can basically be completed by one person. Unlike total station workflows where another person must run around carrying a prism, GNSS surveying can be done efficiently with few people. This helps address labor shortages and reduce labor costs.

• No line-of-sight required and broad-area surveying: As long as satellites are visible, positioning is possible, so the line-of-sight between instrument and prism required by total stations is unnecessary. Even on sites with uneven terrain or obstacles, direct positioning is possible if the sky is open. Large sites or distant points can be observed freely as long as they are within the base station’s effective range.

• Error reduction through high accuracy: RTK GNSS can identify positions to centimeter accuracy, greatly reducing staking errors. This reduces rework caused by accumulated small surveying errors or human mistakes, approaching “zero defects.” Confidence in high accuracy also improves site work quality.

• Immediate use of digital data: Coordinates acquired by GNSS receivers can be recorded digitally and easily reflected in CAD drawings or imported into GIS. You can upload data to the cloud from the field for sharing or reuse it for machine guidance data for construction equipment, making it highly compatible with ICT construction and digital surveying. Eliminating manual transcription to paper improves data processing efficiency.

What you need to start RTK GNSS surveying

To begin high-precision surveying with RTK GNSS, you need certain equipment and preparations. Below is a list of the main required items.

• GNSS receiver for the base station: A GNSS receiver for the base station is required. For high precision, a multi-GNSS, dual-frequency receiver is desirable. Since the base station is installed at a known control point, use a stable, stationary-capable unit.

• GNSS receiver for the rover: This is the GNSS device carried by the operator. Prepare a high-precision GNSS receiver and antenna for the rover as well. The rover is often mounted on a survey pole.

• Communication means (radio equipment or Internet connection): You need a way to deliver correction data from the base station to the rover. If using your own base station, a UHF-band radio set (transmitter/receiver) is commonly used, but be mindful of radio law compliance and licensing. For network RTK, the rover connects to correction information distribution services (Ntrip) via mobile data (mobile router or smartphone tethering).

• Mounting accessories: Equipment for stable installation is also necessary. For the base station use a tripod or fixed pole; for the rover use a survey pole or telescopic pole. These allow the antenna to be set at the specified height and enable stable positioning.

• Controller / surveying software: A controller terminal is needed to configure the GNSS receivers and record positioning data. Dedicated handheld controllers, tablets or PCs with surveying software, or smartphone apps can be used. Through this controller you set up base and rover, check positioning status, and manage coordinate recording.

• Power supply / batteries: Secure power for GNSS receivers and radios. Outdoor work generally relies on battery power. Charge device batteries or prepare spare batteries for long tasks. If using a smartphone or tablet, have a mobile battery on hand.

In addition to the above, actual surveying may require small accessories (tribrach, bubble level, level gauge, field notebook, etc.). Broadly speaking, once you have “a complete set of base station + rover GNSS equipment,” “a communication environment,” and “a terminal to handle positioning data,” you can start RTK surveying.

Basic steps for RTK GNSS surveying

Once you have the necessary equipment, you can begin RTK GNSS surveying. Below is the typical workflow for RTK surveying, explained step by step.

• Base station installation and startup: First install the base station GNSS receiver at a known coordinate point (or a chosen reference point). Secure it on a tripod, check level with a bubble, and power it on to start GNSS positioning. When using your own base station, at this stage the base station itself is still performing normal GNSS positioning and measures position within a meter-level error range. Enter the current coordinate into the base station software or observation, or observe for a certain period (e.g., several minutes to tens of minutes) and use the averaged value as the base station’s provisional coordinates. Then switch the base station to base station operation mode and start broadcasting correction data. For radio, start transmitting; for network operation, send data to an Ntrip server via the Internet.

• Rover startup and correction reception setup: Next power on the rover GNSS receiver and the controller terminal. Once the rover begins receiving satellite signals, configure it to receive corrections from the base station. For radio systems, set the frequency and channel and wait to receive; for network systems, log in to the correction service from the app or software on the terminal. When set up correctly, the rover will begin receiving real-time corrections from the base station.

• Establishing RTK positioning (obtaining FIX): Even after the rover starts receiving corrections, high precision may not be immediate. Check the GNSS receiver display and wait for the solution to change from “FLOAT” or “converging” to “FIX.” This means integer ambiguity resolution has completed and error correction is sufficiently applied. Under good conditions, FIX may be obtained within a few seconds to a few tens of seconds after startup. At initial power-on or when satellite geometry is poor, FIX can take a few minutes. If FIX is not obtained after waiting, check satellite visibility and communication status. Once FIX is obtained, high-precision positioning continues as long as corrections are being received.

• Measuring / observing survey points: After obtaining FIX, start surveying. Place the rover antenna (pole tip) precisely at the point to be measured and record the current coordinates from the controller. If necessary, record for several seconds to tens of seconds and average to obtain a more stable coordinate. Repeat this at each point when surveying multiple points. For staking out or marking design coordinates, input target coordinates into the controller and use the guidance function to fine-tune the position using displayed offsets. Real-time guidance (for example “move 5 cm to the east”) lets you mark the design position once reached. The real-time positioning unique to RTK GNSS allows immediate point confirmation and placement on site.

• Data saving and post-processing: After measuring, save the recorded coordinate data. Assign point names or IDs on the controller or app and export all data. If necessary, convert coordinates to the Japanese geodetic system or plane rectangular coordinate system and plot them in CAD. Cloud-enabled systems allow immediate upload from the field for office review and sharing. Finally, power down base and rover and pack up equipment. These are the basic RTK surveying procedures.

Points and precautions for introducing RTK GNSS

Here are some key points and precautions to ensure successful RTK GNSS surveying. Paying attention to the following when introducing RTK will help smooth operation.

• Secure a good positioning environment: GNSS positioning, including RTK, ideally requires a wide-open sky. In areas shaded by buildings or under trees, satellite signals are blocked and positioning accuracy decreases or FIX is harder to obtain. Try to observe where surroundings have few obstructions, or configure the receiver to exclude blocked-direction satellites. Be wary of strong radio interference sources (near high-voltage lines, etc.).

• Distance between base station and rover: The farther you are from the base station, the larger uncorrectable error factors (ionospheric and tropospheric differences, etc.) become, degrading RTK accuracy. Generally, high accuracy is maintained within roughly 10–20 km (roughly 6.2–12.4 mi), but if possible keep within 5–10 km (3.1–6.2 mi). Even with network RTK, using correction information from nearby reference points improves stability.

• Accuracy of the base station coordinates: When using your own base station, accurately setting its installation coordinates is crucial. If the base station coordinates are in error, the rover coordinates will be correspondingly offset. If absolute coordinate accuracy is required (for official surveys, etc.), connect to national geodetic reference stations or perform long-duration observations to determine the base station position as a known point. Conversely, if only relative accuracy within a local coordinate system is required, you can set provisional base station coordinates and later shift the entire dataset by comparing with known points.

• Antenna height and survey reference: Pay attention to GNSS antenna height settings. If the rover antenna is mounted on a pole, measure the height from the antenna phase center to the ground (survey point) accurately and enter it into the controller. Errors here will cause vertical measurement errors. In Japanese surveying practice, results are often provided in the local plane rectangular coordinate system rather than global latitude/longitude; choose the appropriate coordinate system in your positioning software and set the origin latitude/longitude or geoid height if needed.

• Communication stability: When using radio, ensure stable reception between base and rover by paying attention to antenna orientation and height. In urban areas, signals can be blocked by buildings and relay stations may be required. With cellular networks, mountain areas or underground locations may lack signal and be unable to receive corrections. Check the site’s communication environment in advance and, if necessary, verify carrier coverage or prepare alternative communication methods.

• Check legal and institutional requirements: GNSS surveying itself typically does not require a special license, but using radio equipment requires radio station licenses under radio laws and use of devices with technical conformity certification. Also, accessing national reference station data for network RTK may require paid contracts. For public surveying, ensure RTK-GNSS methods comply with regulations. Familiarize yourself with related procedures and systems before introduction.

Simple surveying with LRTK

RTK GNSS is extremely useful, but traditionally required dedicated surveying equipment and radio setups, which posed a high barrier for beginners. Recently, solutions that lower these hurdles and let anyone start RTK surveying easily have appeared. A representative example is LRTK.

LRTK consists of an ultra-compact GNSS receiver device that can be attached to a smartphone, a smartphone app to operate and manage it, and a cloud service to utilize measurement data. The LRTK device, provided as a smartphone attachment (an integrated high-precision GNSS antenna unit), connects to iPhones and similar devices. Stationary base stations and complex wiring traditionally required are unnecessary; the device obtains correction information (Ntrip) via the smartphone’s network to achieve real-time high-precision positioning. In the field, you can start positioning with the app by pressing a single button, and after a few seconds the current position is displayed with centimeter-level accuracy. It is intuitive and easy to operate without complex setup, making it suitable for non-experts.

Because it links with a smartphone, you can also attach photos or notes to measured point data and immediately upload them to the cloud for sharing. This digitizes and shares field-collected information on the spot, reducing post-work data cleanup. LRTK makes it easier and faster than ever to adopt high-precision GNSS surveying. If you want to benefit from RTK GNSS more easily, consider introducing modern solutions like LRTK to your site. It should dramatically improve surveying efficiency and accuracy.

FAQ

Q: What is the difference between “RTK-GNSS” and “GPS”? A: GPS is a type of GNSS and a standalone GPS receiver typically only achieves meter-level accuracy. RTK-GNSS, on the other hand, uses correction information from a base station to correct errors in real time and achieve centimeter-level accuracy. Simply put, while GPS positions alone, RTK-GNSS greatly improves positioning accuracy through communication between two receivers.

Q: What accuracy can RTK-GNSS achieve? A: Under good conditions, you can expect about 1–2 cm (0.4–0.8 in) horizontal accuracy and about 2–3 cm (0.8–1.2 in) vertical accuracy. Actual accuracy depends on distance from the base station, satellite geometry, and surrounding environment, but it is vastly superior to standalone GPS positioning (meter-level errors). Note that the obtained accuracy is relative, so the more accurate the base station position, the higher the absolute accuracy of the results.

Q: How long does it take to achieve high-precision positioning? A: The time from powering on the GNSS receiver and starting to receive corrections until obtaining a FIX solution varies by environment, but can be as short as a few seconds and generally within a few minutes. Modern receivers and good satellite visibility can yield a fixed solution in a few to several seconds. On the first startup or with few visible satellites, it may take longer. Once in FIX, high precision is maintained as long as corrections are received, allowing continued surveying without special waiting time.

Q: Can RTK surveying be done without a base station? A: Yes. Even without setting up your own base station, you can perform high-precision positioning using network RTK. This connects via the Internet to correction services provided by networks of reference stations, such as national geodetic reference stations, and uses their correction data. For example, by contracting with national electronic reference station networks or private VRS services, you can bring only the rover to the field and perform positioning. As long as cellular service is available, you can obtain correction data in real time without a local base station.

Q: Can RTK-GNSS be used in mountainous or forested areas? A: Satellite positioning requires receiving signals from satellites overhead. In valleys surrounded by mountains or within dense forests, the number of visible satellites decreases and RTK positioning can become difficult. Dense tree canopies cause signal blockage and multipath reflections, making FIX harder to obtain. While not impossible, accuracy may degrade and coverage may be intermittent. In mountain areas where the sky is open (ridges or valley mouths) positioning is easier, but in deep valleys or tunnels GNSS positioning is essentially impossible. For such environments, plan surveys for times with favorable satellite geometry or supplement with optical surveying instruments.

Q: Are RTK-GNSS devices expensive? A: Traditional survey-grade GNSS equipment has often been expensive, ranging from hundreds of thousands to millions of yen. However, advances in low-cost GNSS chips and open-source technology have produced receivers capable of RTK at lower cost. Examples include small receivers costing tens of thousands of yen and relatively inexpensive smartphone-compatible products. Costs are decreasing, but professional-grade accuracy and reliability still require investment. Given the significant gains in work efficiency and labor savings from RTK-GNSS, the cost-effectiveness is very high.

Q: What RTK-GNSS equipment is recommended for beginners? A: For first-time users of high-precision GNSS surveying, smartphone-compatible RTK solutions are recommended. Products like LRTK, introduced in this article, let you attach a device to your phone and start positioning with a single button, offering ease of use. Those unfamiliar with dedicated equipment can comfortably manage position data via user-friendly smartphone apps. While combining open-source RTK software with commercial receiver modules is possible, it requires more knowledge for setup and tuning. To reliably experience centimeter-level positioning, using a supported commercial simple RTK product (e.g., LRTK) is the quickest path.