Creating a Standard Operating Procedure (SOP) for RTK in Construction Layout

Table of Contents

• Introduction

• What is RTK?

• Benefits of Using RTK for Construction Layout

• Importance of Establishing an RTK Standard Procedure (SOP)

• Standard Procedure for Construction Layout Using RTK

• Operational Precautions and Best Practices for RTK

• Simplified Surveying with LRTK

• FAQ

Introduction

In recent years, high-precision positioning using RTK has attracted attention for surveying and layout work on construction sites (such as marking out and installing batter boards). RTK is a technology that uses GNSS (satellite positioning) to determine positions in real time with centimeter-level (half-inch-level) accuracy, enabling efficient and accurate operations. However, correct operation of RTK equipment on site requires certain procedures and knowledge. This is where a Standard Operating Procedure (SOP) becomes important. This article explains how to create a standard procedure (SOP) for using RTK in construction layout tasks. We will go through concrete steps and key points in detail so that anyone on site can perform RTK surveying safely and reliably following the same procedure.

What is RTK?

RTK (Real Time Kinematic) is a surveying method that uses two GNSS receivers—a base station and a rover—and corrects positioning errors in real time to obtain high-precision positions. Ordinary GPS positioning can have errors of several meters (several ft), but RTK positioning can reduce errors to within a few centimeters (within a few inches) by applying correction information. For example, a base station with a known position is set up on site; that base station continuously computes the GNSS signal errors it receives and transmits the corrections via radio or the internet. The rover that moves around the site receives those corrections and applies them to its own observations to compute high-precision coordinates in real time. Through this mechanism, RTK achieves millimeter- to centimeter-level accuracy that cannot be obtained by standalone positioning. In the construction industry, RTK’s feature of “instant high precision” is being leveraged across various surveying and layout tasks.

Benefits of Using RTK for Construction Layout

Introducing RTK for layout tasks (layout surveying) on construction sites provides many benefits compared to traditional methods. First is a significant improvement in work efficiency. Tasks that previously required two people—such as stringing batter boards or driving stakes using total stations and maintaining line of sight—can be done quickly by one person simply walking with a GNSS rover when using RTK. Even on sites with many obstacles, as long as radio signals from the satellites reach the receiver, positioning is possible at points without line of sight. Second is improved point accuracy. Because RTK continuously corrects signals from satellites, it can provide point positions with centimeter-level (half-inch-level) accuracy. This allows design coordinates to be reproduced on site accurately, minimizing misalignment of structures and elevation errors and ensuring construction quality. Third is labor and personnel savings. RTK-GNSS is also used for machine guidance and as-built measurement on equipment, enabling data collection while reducing manual effort. The Ministry of Land, Infrastructure, Transport and Tourism’s *i-Construction* initiative has also encouraged the spread of ICT construction using RTK. In this way, using RTK for construction layout enables “fast, accurate, and efficient” surveying, contributing to overall site productivity and quality improvement.

Importance of Establishing an RTK Standard Procedure (SOP)

To reliably use advanced positioning technology like RTK on site, standardized work procedures are indispensable. An SOP (Standard Operating Procedure) is a document that codifies procedures so that anyone performing the work obtains the same results. There are several important reasons to establish an SOP for RTK operations. First, it helps prevent operational errors. In RTK surveying, mistakes in base station setup or equipment handling can lead to large measurement errors. By defining standard procedures—such as “reconfirm the coordinates of the known point when installing the base station” and “always enter the antenna height”—important items are executed without omission, reducing human error. Next, SOPs facilitate onboarding of new staff. Less experienced technicians can perform RTK surveying with a certain level of quality and safety by following the SOP. Although RTK operation tends to require specialized knowledge, a procedural guide helps smooth site adoption. SOPs also improve response to equipment troubles by including wireless setup methods and troubleshooting steps (for example, reset procedures when a FIX solution cannot be obtained). If these are shared in advance as standard procedures, on-site staff can calmly respond to issues. Additionally, SOPs help protect expensive equipment. RTK receivers and antennas can cost millions of yen; by defining correct setup and teardown procedures in the SOP, the risk of damage or loss is reduced. For these reasons, creating an SOP when introducing RTK is critical for ensuring accuracy, safety management, and knowledge transfer.

Standard Procedure for Construction Layout Using RTK

Now let’s look at a typical series of steps for construction layout work using RTK. The steps below are an example of the basic flow that should be included in an SOP.

Step 1: Preparation

Before going out to the site to begin surveying, make sure to prepare the necessary equipment and data. It is not an exaggeration to say that the success or failure of the survey is determined by pre-survey preparation. Specifically, prepare the following items.

• Complete GNSS surveying equipment set (RTK-capable GNSS receiver set): prepare two receivers for base and rover, plus antennas, tripods, prism poles (or pole-integrated antennas), batteries, mounting brackets, and other accessories needed for on-site positioning. If you will not install your own base station (see network RTK below), a rover receiver and a communication terminal may suffice.

• Survey controller or app: prepare a dedicated field controller or a tablet/smartphone with a surveying app to control the GNSS receiver and display/save positioning results. Install the software compatible with your equipment in advance and confirm basic operations.

• Design documents and coordinate data: prepare design drawings and a list of coordinates of points to be laid out. If you have electronic data (CAD files or CSV coordinate lists), import them into the controller beforehand. Confirm the survey coordinate system (e.g., plane rectangular coordinate system zone X) and reference height point information and align the equipment settings accordingly.

• Communication means: prepare the communication environment to receive RTK corrections. For radio link between base and rover, prepare paired radios (e.g., low-power specific radios) and set frequencies and IDs in advance. For network RTK (Ntrip), ensure the rover has internet access. Prepare smartphone tethering or mobile routers and complete contracts and connection settings for correction services (VRS etc.).

• Other items: don’t forget tools for driving stakes or marking (wooden stakes, nails, hammers, chalk or spray for marking). Also prepare worker safety items such as sun protection and hydration supplies.

After preparing sufficiently, perform equipment functional checks. For peace of mind, power up GNSS receivers and test by measuring a known point at your office or an open outdoor area to confirm accuracy. Fully charge batteries the day before and prepare spare power sources so you can go to site in a fully prepared state.

Step 2: Base Station Setup and Configuration

Upon arrival at the site, first perform the base station setup. The base station plays an important role as the reference for RTK surveying, so install it carefully. The basic flow is as follows.

First, secure a reference point. If possible, select a public control point (a known point) near the site or a point whose coordinates have been previously surveyed as the installation location for the base station. Installing on a stable known point guarantees absolute accuracy based on the geodetic datum. If no appropriate known point exists, you may establish a temporary reference point within the site, but in that case you must later tie that point to other control points and apply coordinate corrections.

Next, install the antenna. Set up a tripod in an open location with as wide a view of the sky as possible. Fully extend and stabilize the tripod legs and fix them to the ground. Mount the antenna on the tripod while checking level with the supplied tribrach or bubble level. Align the antenna directly over the reference point with a plumb bob and secure it so it does not shift. Accurately measure the antenna height (the height from the antenna’s reference point to the ground reference point) and enter it into the controller. Errors in this value will shift all height results, so exercise care.

Then, configure the base station receiver. Power on the base GNSS receiver and set it to base station mode via the controller or PC. If you have known point coordinates, input them to set the base station position (e.g., coordinates in the Japanese geodetic system JGD2011 for the relevant zone). If using a temporary reference, set the automatically measured value as a provisional coordinate and record it so it can be corrected later.

Also ensure communication establishment. Prepare the method to transmit correction data from the base to the rover. For radio, connect the base receiver to the transmitter and match frequencies/channels with the rover receiver (use licensed frequencies if required). For network RTK, the base station only needs to be installed; communication is handled by remote correction services accessed by the rover. Confirm that the base receiver has started operating and broadcasting corrections—once confirmed, base station setup is complete.

Step 3: Rover Startup and Initialization

With the base station ready, move to rover setup. Power on the rover GNSS receiver and the controller (or smartphone/tablet) and begin positioning.

First, set the controller to RTK positioning mode so it can receive correction information. For radio-type systems, set the receiver to receive signals from the base transmitter. For network-type systems, start the Ntrip client (correction service app) and connect to the designated server. Once correction data is being received, the rover will apply real-time corrections to its positioning.

As GNSS satellite lock improves and corrections are applied, the positioning solution status will change from FLOAT to FIX. A FIX solution is the high-precision solution where integer ambiguities have been resolved; only with FIX do you attain centimeter-level (half-inch-level) accuracy. Therefore, before starting layout work with the rover, always confirm that the solution is FIX. Check the controller or app display for a “FIX” indicator or RTK status; if it remains FLOAT, check satellite count and signal conditions. Perform initialization (restart or re-computation) as needed to obtain a reliable FIX before proceeding.

Also perform tilt sensor calibration if the rover has a tilt compensation feature. Hold the pole vertically and follow the prescribed calibration procedure so that correct positioning is maintained even when the pole is tilted. Once these initial settings are complete, you are ready to proceed with RTK positioning. From then on, carry only the rover to visit each point and continue layout work.

Step 4: Performing the Layout Work

Now begin the construction layout (marking) tasks. Use the controller or surveying app to call up the design coordinates you registered in advance and mark or stake out points on site.

First, on the controller select the point to be laid out—for example, “centerline of a building column” or “corner of a foundation” from the design coordinates. Surveying apps usually include a guidance (navigation) function that displays the difference (distance and bearing) between the current rover position and the target coordinate in real time. Use this to move the rover toward the target point.

While moving the rover (pole tip), fine-tune the position following the controller display. As the distance to the target decreases, messages such as “horizontal error less than 1 cm” or “arrived” will appear—this indicates the design coordinate location. Perform marking or stake driving. The pole tip (the tip of a prism pole or the foot of a marking pole) is the precise point on the ground to mark. If driving a wooden stake, move the receiver aside while driving the stake, then place the receiver back on the stake to verify the position (to check for any displacement caused by driving). When installing batter boards, use RTK to determine and place the stakes that will act as anchor points for the ropes.

Repeat this process for all points that require layout. It is crucial to maintain a FIX RTK solution at all times. If the solution reverts to FLOAT during work, immediately pause positioning at that location and wait for FIX again or reinitialize. Positioning with FLOAT increases errors and negates the advantage of high-precision positioning. Always monitor reception status and correction availability while working.

It is also important to perform periodic verification measurements. For example, during a sequence of layout tasks, re-measure known control points or recently placed stakes to check for drift. If a discrepancy of several centimeters or more is found, the base station may have moved or a system error could have occurred. In such cases, immediately investigate the cause and, if necessary, review previous measurements. Although RTK is convenient, its real-time nature requires ongoing verification to ensure reliable results.

Step 5: Results Verification and Pack-Up

After completing layout for all points, perform final verification and post-processing. Properly concluding this step ensures the accuracy and reproducibility of RTK surveying.

First, verify the survey results. The coordinates recorded by the rover should be saved in the controller or app—check them in a list for any obviously wrong values (e.g., wildly out-of-range numbers or measurement errors). Perform on-site validation as needed. For example, re-measure known points used for the base and confirm that their coordinates are correct. Observing the same control point at the start and end of the day and comparing the results is effective; if the difference between start and finish is negligible, it indicates the day’s surveying was stable.

Next, pack up equipment. Power down the rover and store equipment in order. Power off the base station last, remove the antenna from the tripod, and stow it. If you have recorded antenna heights and other notes, compile these records. Wipe mud or moisture off tripods and poles before storing, and transport precision instruments carefully to avoid damage.

Finally, save and share results. Transfer survey data from the controller to the company PC or cloud storage and make backups. Compile lists of point coordinates and check results, and, if necessary, reflect them in CAD drawings. It is helpful to standardize data management rules—e.g., “create a folder per site and save files with date and task name in the filename.” Proper data storage aids later verification and additional works.

The above outlines a typical flow for construction layout using RTK. We recommend customizing these steps to match your organization’s operations and documenting them as your own SOP.

Operational Precautions and Best Practices for RTK

In addition to the above steps, here are points to keep in mind to perform RTK surveying stably. Below are operational precautions and best practices.

• Ensure accuracy of base station coordinates: Use the most accurate coordinate values possible for the base station. It is ideal to use reliable known points such as fourth-order triangulation points or continuously operating reference stations. If you operate a temporary base, perform accurate coordinate surveying later and apply a bulk correction to all measured points. If the base station position is off by 1 m (3.3 ft), the acquired coordinates will all be uniformly off by 1 m (3.3 ft). If absolute position accuracy is required, the base station accuracy is crucial.

• Thorough antenna setup and height entry: Always secure and level the antenna. Especially, keep the rover pole as plumb as possible and check verticality with the pole’s bubble before measurement. Mistakes in entering antenna height are a major error source. Measure the antenna height precisely with a tape and enter it correctly into the software. Even a small height input error can cause vertical displacement, so specify in the SOP to “enter antenna height ○ cm (○ in)” and ensure it is done.

• Ensure good satellite reception conditions: RTK relies on satellite signals and is highly affected by surroundings. The rule is to position in as open a sky view as possible. Under building eaves or trees, satellites may be insufficient and reflected signals (multipath) can degrade accuracy. If you must measure near obstructions, consider longer static times or choosing times with favorable satellite geometry. Including steps like “check sky visibility around the measurement point beforehand” in the procedure is helpful.

• Utilize multi-GNSS and multi-frequency capabilities: If possible, use receivers that support multiple satellite constellations and multiple frequencies. Using GPS, GLONASS, Galileo, and QZSS (Michibiki) together increases satellite availability and improves accuracy and stability. Multi-frequency receivers (e.g., L1/L2) enhance ionospheric error correction and typically achieve FIX solutions faster. New services such as Japan’s QZSS centimeter-class augmentation service (CLAS) are also available; compatible receivers can receive centimeter-class corrections without external communication, which is useful when communication is unreliable.

• Continuous accuracy checks: Make it a habit to check accuracy regularly during work. For example, observe the same known point at the start and end of day and compare. If there is no significant difference, the system was stable for the day. Large discrepancies indicate the need for correction or re-survey. If the rover’s solution reverts from FIX to FLOAT during measurement, stop and wait for FIX before re-measuring. Document these accuracy management rules in the SOP and enforce them on site.

• Averaging measurements: When needed, you can further improve accuracy by time-averaging measured values instead of using instantaneous results. While RTK provides immediate results, for points requiring higher precision it is effective to remain stationary for several seconds to several tens of seconds and average the readings. Vertical (Z) values tend to fluctuate more, so when possible, observe multiple times and use the average. Including guidelines such as “measure important points while stationary for 10 seconds or more” in the SOP is recommended.

By following these points, RTK surveying accuracy and reliability will improve. The keys to maintaining high precision are “accurate reference,” “good reception environment,” “utilization of equipment capabilities,” and “continuous monitoring.” Rigorously following the basics enables you to maximize RTK’s potential.

Simplified Surveying with LRTK

So far we have described standard surveying procedures and precautions using RTK equipment. Recently, solutions that simplify these operations and make RTK surveying even more accessible have emerged. A representative example is the approach known as LRTK.

LRTK (L-RTK) combines a smartphone with a small high-precision GNSS receiver to enable centimeter-level (half-inch-level) positioning with portable equipment. Traditional RTK hardware has been large, expensive, and difficult to handle; LRTK greatly lowers that barrier, enabling the feel of “your smartphone becomes a high-precision surveying instrument.” With a small dedicated receiver (an attachment for a smartphone) and an app, you can take measurements on the spot, record them, and share necessary information via the cloud—all from the smartphone. It realizes an environment where “anytime, anywhere, anyone” can perform high-precision surveying.

Using LRTK, centimeter-class positioning that previously required surveying specialists can be performed directly by site supervisors and technicians. Pocket-sized equipment allows immediate measurement and sharing, reducing the time spent waiting for survey teams or stopping machinery for layout, directly improving site productivity. The cumbersome process of recording notes on paper and later digitizing them is eliminated as data is automatically saved to the cloud, enabling quick reflection in office drawings and team sharing. LRTK systems are designed to be affordable, promoting the concept of “one versatile surveying device per person,” and have quietly gained popularity on many sites. It has been demonstrated that LRTK can achieve accuracy comparable to dedicated equipment, making it an ideal choice for those trying RTK surveying for the first time.

Thus, advances in RTK technology and surveying tools are making construction site surveying increasingly simple and sophisticated. By incorporating new solutions into existing SOPs, further labor-saving and efficiency gains can be expected. Please make appropriate use of proper procedures and the latest technologies to improve the quality and productivity of construction layout work.

FAQ

Q: How accurate is RTK surveying? A: Generally, RTK surveying provides accuracy on the order of a few centimeters (a few inches) in horizontal position. Under good conditions, horizontal positions of 1-2 cm (0.4-0.8 in) and vertical (height) within a few centimeters (a few inches) have been confirmed. Accuracy varies with satellite reception conditions and distance from the base station, but it is orders of magnitude more precise than standalone positioning (meter-level errors). To further improve accuracy, measure in open sky conditions and remain stationary for several seconds to take averaged measurements.

Q: Do you have to set up a base station every time for RTK surveying? A: It is not always necessary to set up your own base station. With network RTK, a network of continuously operating reference stations (such as national geodetic control points) provides corrections via the internet (VRS etc.). In this case, users only need a rover and can start RTK surveying without placing a physical base on site. However, network RTK requires service contracts and communication access. In remote mountain areas where network connectivity is difficult, setting up your own base station remains effective. Choose between base-station and network modes depending on site conditions.

Q: Is a radio station license required for RTK surveying? A: When transmitting correction information via radio, a license may be required depending on the frequency used. For example, specific low-power radios (e.g., around 920 MHz) can be used without a license, but higher-power UHF radios (e.g., around 400 MHz) that achieve longer ranges typically require licensing from the Ministry of Internal Affairs and Communications. Network RTK over cellular networks removes the need for radio licensing. Nowadays, license-free radios and internet communications are common, and RTK surveying can often be performed without special radio licenses.

Q: Can RTK surveying be done by one person? A: Yes, it is basically possible for one person to work alone. One advantage of RTK surveying is labor reduction. Traditional total station surveys required at least two people (an operator and a prism holder). With RTK, once a base station is set up, a single person can carry the rover and measure points. Network RTK eliminates the need to set up a base, enabling completely solo operation. This makes it easy for site supervisors to check measurements themselves over large sites without allocating extra personnel. However, for safety reasons in mountainous or hazardous environments, working in teams may be preferable; judge based on the situation.

Q: What is LRTK? A: LRTK is a new RTK positioning solution that leverages smartphones. By attaching a small dedicated GNSS receiver to a smartphone or tablet and using a dedicated app, centimeter-class surveying becomes possible without expensive traditional surveying equipment. In the system provided by Refixia (for example), the smartphone acts as both the controller and data storage device, and positioning data is saved to the cloud in real time. In short, it’s the idea of “a smartphone becoming a high-precision GPS receiver,” allowing anyone to easily start RTK surveying. The equipment set is simple—just the receiver and a smartphone—so initial investment is lower than for conventional systems.

Q: Can people without specialized knowledge use LRTK effectively? A: Yes, it is relatively easy to use. LRTK apps are designed with intuitive interfaces, and those familiar with map apps will quickly get used to them. Basic operations are simple—select the point you want to measure and press a button to record—while complex calculations and settings are handled by the app. Since tasks that used to require separate devices—measuring, recording, taking photos, and making notes—are integrated, even non-experts can reliably acquire data without omissions. The ease of learning while using on-site is another attractive feature of LRTK.