RTK Surveying Procedure and Key Points Using the LRTK Terminal

Preparation Before Surveying (Equipment, Environment, Settings)
Before conducting RTK surveying using the LRTK terminal, there are several preparations that need to be made in advance. It is important to check the equipment, confirm the working environment, and set up the necessary survey settings. Below are the key points to check before starting the survey.

• Confirming Necessary Equipment:
  Check that the LRTK terminal and the corresponding smartphone are available for use in the survey. The LRTK terminal (e.g., LRTK Phone) is a compact device that integrates the antenna, GNSS receiver, and battery. Prepare either an iPhone or an Android device (ensure compatibility) and install the dedicated "LRTK app" beforehand. Additionally, fully charge the smartphone and the LRTK terminal’s batteries, and prepare a mobile battery if necessary. A monopod, pole, or spirit level can be helpful for ensuring stable positioning of the terminal, making it easier to install the device accurately at the survey point.

• Confirming the Work Environment:
  For GNSS surveying, it is ideal to have an open view of the sky. Check the surrounding environment of the survey site in advance and select a location that minimizes interference from buildings or trees, as well as the impact of signal reflections (multipath). Be cautious in environments such as under viaducts or in tunnels, where satellite signals may not be adequately received, making RTK positioning difficult. In urban areas with tall buildings, where satellites are easily blocked, consider adjusting the positioning points or extending the measurement time for averaging. Additionally, RTK surveying requires a communication environment to receive correction data from the base station. Typically, correction data is obtained via internet communication, so verify in advance that mobile communication is available at the site (solutions for areas without mobile signal, such as underground or mountainous regions, are discussed later).

• Positioning Method and Correction Data Preparation:
  When using the LRTK terminal, decide in advance how to obtain correction information (base station data). Common options include:​

  • Network RTK:
    Correction data can be obtained via the internet from the Geospatial Information Authority of Japan’s electronic reference point network, private base station services, or publicly available "voluntary base stations" (commonly referred to as "free base stations"). In the LRTK app, configure the Ntrip client by entering the Ntrip server address, port, mount point, and login information as specified by the provider. By choosing base station data (or virtual reference station VRS) suitable for the survey region, high-precision corrections can be obtained.

  • Setting up Your Own Base Station:
    If there are known reference points near the site or if your company operates its own RTK base station, use that base station. Install another GNSS receiver (either the LRTK terminal or another RTK receiver) at a known point on-site and set it to base station mode, then transmit correction data to the moving LRTK terminal via Wi-Fi or short-range radio (920 MHz band). If using higher-end models like the LRTK Pro series, which include wireless communication, RTK positioning can be performed directly without an internet connection. However, for your own base station, you need to determine and set the exact coordinates of the point in advance.

  • CLAS (Michibiki’s Correction Signal):
    For sites where internet access is unavailable, such as in mountainous areas or locations without cellular service, you can use the centimeter-level positioning correction service (CLAS) provided by the Quasi-Zenith Satellite System (Michibiki). Some LRTK models (e.g., LRTK Phone 4C off-grid model) can directly receive CLAS signals, allowing high-precision positioning even when the smartphone’s communication signal is unavailable. Ensure the location is within the coverage area (CLAS is available across nearly all of Japan) and that the terminal model supports it.​

• App Settings and Coordinate System Confirmation:
  Launch the LRTK app and confirm all necessary settings for positioning. First, establish a Bluetooth connection between the terminal and the smartphone and ensure the app is receiving GNSS data from the LRTK terminal. Then, input the correction data settings (for Ntrip or CLAS) and confirm that the correction information is being received properly. Additionally, confirming the output coordinate system for the survey results is crucial. In Japan, civil engineering surveys typically use the "World Geodetic System (Japan Geodetic System 2011 / JGD2011 or JGD2020) plane rectangular coordinate system." In the app, select the appropriate plane rectangular coordinate system number for the work area and configure the geoid height (elevation derived from the geodetic height). This setup allows for direct comparison with the Geospatial Information Authority of Japan’s reference points or design drawings. It’s a good idea to test the system by measuring a known point to ensure the coordinate system and positioning accuracy are correct.

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Once these preparations are made, you can smoothly transition to RTK surveying using the LRTK terminal. Don’t overlook any part of the preparation stage—ensure the equipment and settings are fully in place before heading out to the site for surveying.

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Actual Surveying Procedure (Setup, Establishing Reference Points, and Positioning Methods)

Once the preparations are complete, it is time to begin the RTK surveying work on-site. Below, we will explain the specific surveying procedure using the LRTK terminal, following the flow of "setup," "establishing reference points," and "positioning methods."

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1. Setup on Site:
Upon arriving at the survey site, first, set up the LRTK terminal and smartphone to be ready for use. Turn on the terminal and confirm that the Bluetooth connection with the smartphone has been established. Next, hold the smartphone in a way that makes it easy to survey. You can hold it in your hand, but if possible, attach the smartphone to the included monopod or pole, and adjust the pole's tip (bottom) to align with the point to be measured. When using a pole, check the vertical alignment with a spirit level and adjust so that the LRTK terminal is positioned directly above the survey point. After setup, launch the LRTK app and start capturing GNSS satellites. Check on the app's display that the number of visible satellites is sufficient and that correction data is being received (check the status of the base station data). Once the correction data is correctly applied, the positioning mode will usually switch from "Float" to "Fix." A "Fix" means that integer cycle resolution is complete and centimeter-level accuracy is achieved, which is crucial for RTK surveying.

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2. Confirming and Establishing Reference Points (Known Points):
In RTK surveying, it is necessary to verify whether the positioning results from the base station are based on a known reference coordinate system. When using network RTK or CLAS, the base station provides information tied to a public coordinate system (such as the World Geodetic System), but it’s advisable to use a known reference point on-site for accuracy verification. For example, if there are trig points or electronic reference points set by the Geospatial Information Authority of Japan nearby, or pre-surveyed benchmarks (known coordinate points) at the construction site, measure them using the LRTK. Compare the measured coordinates with the known coordinates, and if the error is within a few centimeters, you can confirm that the system is operating correctly. If the difference is large, it’s likely an issue with the coordinate system settings or correction data, so be sure to review the setup.

Additionally, you can establish a reference point before starting the work. This is useful, for example, when deciding on new reference points to use for measurement or quality control at a construction site. Select a stable location (preferably a place with a clear view on the site) and perform static measurements for a set period to obtain high-precision coordinates. The LRTK app also has a feature that averages multiple observation values, and by using this averaged measurement, you can obtain a more accurate reference point coordinate. By performing measurements at a specific point multiple times and averaging the results, the error will decrease, and the precision will improve. Once this reference point is established, it will make subsequent measurements, such as developing local coordinate systems or matching with existing drawings, easier. If you establish a reference point on-site, mark its location and record the coordinate values.

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3. Positioning Methods for Each Measurement Point:
After completing the setup and verifying the reference points, you can move on to the actual measurement of the survey points. The LRTK app allows you to switch between single-point positioning mode and continuous positioning mode (logging) depending on the application. When measuring individual points, use the single-point positioning mode and place the terminal at the desired location, tapping the positioning button on the smartphone screen. The high-precision coordinates for that moment will be recorded. The data recorded will include latitude, longitude, height (either ellipsoidal height or elevation), date and time, point name (serial number), and the positioning quality information, including the RTK "Fix/Float" status. The app also provides a feature to add a name or notes to the point, so it’s a good idea to label the point with a name like "Foundation Corner Point" for later reference.

For measuring many points continuously while moving through the survey area or scanning terrain, use the continuous positioning mode (logging). When you start the logging function in the LRTK app, the terminal will continuously record positions at a set interval (e.g., 10 points per second). By using this mode, you can measure the elevation of the ground surface across the site while walking, or collect 3D point cloud data of the shape around structures. If using a device like an iPhone with a LiDAR scanner, you can combine LiDAR point cloud measurement with RTK positioning to conduct high-density 3D surveying. During the measurement, continuously monitor the positioning state on the app screen (whether it is "Fix," what the accuracy indicators are), and if the state temporarily reverts to "Float," exclude that section of data or re-measure that area.

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4. Application to Surveying and Guiding (Stakeout and Positioning):
The high-precision position information obtained from RTK surveying can also be used for tasks beyond just measuring points, such as stakeout operations. The LRTK app has a function that allows you to set a target point, either from previously recorded points or coordinates on a drawing, and navigate the current position to that target by showing the distance and direction. For example, when recreating the measured coordinates on-site (stakeout), selecting the target point will display arrows and distances on the smartphone screen to guide you toward the target. Using the AR (augmented reality) mode, the smartphone camera view will overlay a guide arrow indicating the direction to the target point, allowing you to reach the designated location without marking it on the ground, simply by following the on-screen instructions. Additionally, by using a surveying pole and separating the smartphone from the terminal, you can fine-tune the positioning directly above the point, ensuring precise stakeout. This way, using the LRTK terminal, you can handle everything from point measurement to stakeout by yourself, greatly improving on-site productivity.

This concludes the basic surveying procedure using the LRTK terminal. Depending on the site conditions, alternate between single-point positioning and continuous positioning to efficiently collect the required data with high precision. It is important to always check the device and app status during surveying and strive for accurate measurements.

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Verification of Survey Results and Data Utilization

The survey results obtained on-site are just coordinate data in their raw form, but by properly verifying, processing, and utilizing them, significant value can be created. In this section, we will explain how to verify the data obtained with LRTK and key points for utilizing the data both on-site and in the office.

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1. Verification of Survey Results and Accuracy Check:
After completing the survey, the first step is to verify the quality of each point data collected. Display the list of survey points on the LRTK app and check the positioning status (Fix/Float), estimated errors, number of satellites, and other log information for each point. Points obtained with a Fix solution are generally of high precision, but if points are recorded in a Float solution or with insufficient satellite numbers, those points require attention. If necessary, re-measure the point or use averaged values to increase reliability. Additionally, comparing the coordinate differences of the same point measured multiple times (for example, measuring the same position on the way there and back) helps confirm repeatability. If known points were surveyed during the mission, accuracy verification can be done by comparing with those points. These checks help identify surveying errors or mistakes early, ensuring the reliability of the data.

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2. Data Storage and Backup:
Survey data obtained through the LRTK app is stored not only on the device but also can be utilized in conjunction with the cloud service "LRTK Cloud." After the survey, all point data, photos, and point cloud data can be uploaded to the cloud with a single tap from the app. By saving the data to the cloud, even if the field device is damaged or lost, the data will be preserved, and the hassle of transferring the data via cable back to the office is eliminated. Uploaded data can be accessed through a web browser, allowing immediate review of the field data from a PC at the office. While it is also possible to operate locally without the cloud, utilizing the cloud is highly effective for reliable backups and immediate sharing.

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3. Methods for Utilizing Survey Data:
The high-precision data obtained can be used in various ways. Here are some typical examples of data utilization:

• Drawing Creation and CAD Integration:
  Based on the measured coordinate points, create floor plans and cross-sectional drawings, or overlay them with design drawings to check the as-built positions. By exporting the coordinate data from the LRTK Cloud or the app in CSV or DXF format and importing it into AutoCAD or surveying CAD, you can immediately begin the drawing process. Point clouds that were previously recorded in handwritten field books can now be directly converted into CAD drawings as digital data, significantly improving work efficiency.

• As-Built Management and Quality Assurance:
  At construction sites, it is necessary to manage and demonstrate the accuracy of completed structures or leveling. The coordinate values obtained with LRTK meet the accuracy required by the Ministry of Land, Infrastructure, Transport and Tourism’s guidelines for electronic submission and as-built management, allowing for direct demonstration of the as-built positions without relying on photogrammetry results. For example, when inspecting the position of curbstones in road construction, you can compare the design coordinates with the measured coordinates to evaluate discrepancies. If the data is organized in Excel, it can be directly used for report creation.

• Point Cloud Data Analysis:
  3D point cloud data obtained through continuous positioning or LiDAR scanning represents the site’s terrain or structure shapes in high density. By utilizing this, advanced analyses such as volume calculations for earthworks, deformation analysis, and even comparisons with 3D models can be performed on-site. For example, you can scan the ground in a specific area with LRTK, then automatically calculate the volume of embankment and excavation from the point cloud data before operating heavy machinery. Additionally, the point cloud data can be overlaid with 3D city model data (PLATEAU) or BIM/CIM models published by the Ministry of Land, Infrastructure, Transport and Tourism, enabling design comparisons and preliminary reviews.

• Integration of Photo Records and Location Information:
  When taking photos with the LRTK app, high-precision location coordinates and orientation information are tagged to the photos. This turns them into data that not only records the image but also accurately specifies "when, where, and in which direction the photo was taken." In infrastructure inspections, by attaching location data to photos of cracks or damage and saving them to the cloud, the office can review the points on the map and easily identify the same location during future inspections. Even when there are many photos, it is easy to organize them, as the captured locations are plotted on a map in the cloud. This is also helpful when creating reports.​

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In this way, the survey results obtained with the LRTK terminal are instantly stored as digital data and can be effectively utilized even outside the field. The key is not to leave the data unchecked but to thoroughly verify and, if necessary, process and share it. Especially on construction sites where speed is essential, sharing the data on the cloud the same day it is collected and advancing data checks and drawing creation among stakeholders will lead to smooth project management without delays.

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Points to Note and Troubleshooting During Surveying

While LRTK allows for easy high-precision surveying, it is still a precision instrument, and given the nature of GNSS positioning, there are certain points to be aware of and potential issues that can arise. In this section, we’ll summarize important considerations and troubleshooting tips to help ensure smooth surveying operations on-site.

• Maintaining Satellite Reception:
  The accuracy of RTK surveying is greatly influenced by the satellite signal reception. During surveying, try to avoid obstructions in the sky as much as possible. Pay careful attention when passing under buildings or through wooded areas to ensure the number of satellites doesn’t drastically decrease. If the solution temporarily drops to Float, moving to an open area will usually restore the Fix. However, data taken immediately after returning to Fix may not be stable, so it’s better to wait a bit for the accuracy to stabilize before measuring. If there are tall buildings blocking satellites in a specific direction, consider slightly adjusting the measurement point or schedule the survey at times when the satellite configuration (GDOP) is favorable. Using satellite visibility prediction tools, such as those provided by the Geospatial Information Authority of Japan, can help plan the optimal satellite configuration for different times of day.

• Multipath Errors:
  In urban areas or near structures, multipath errors can occur when satellite signals are reflected off walls or the ground, reaching the receiver. Multipath can cause errors ranging from a few centimeters to, in some cases, several tens of centimeters. To avoid this, try not to measure near reflective surfaces and elevate the antenna to more easily receive direct signals. Although the LRTK terminal is high-performance, its antenna diameter is small, so using a dedicated pole to elevate the terminal slightly can help improve accuracy. If the positioning results near the survey point are inaccurate or the precision deteriorates, it may help to stay still for 30 seconds to 1 minute and average multiple observations to reduce errors. It’s important to discard questionable data and retain only the most accurate data in the field.

• Communication and Correction Data Issues:
  If mobile communication is lost while using network-based RTK, correction data can no longer be received, leading to a deterioration in accuracy (in the worst case, the system may revert to standalone positioning with errors of several meters). When working in tunnels or mountainous areas, it’s advisable to plan offline strategies in advance. Utilizing CLAS-capable models, as mentioned earlier, is one example, but other options include setting up temporary mobile communication environments on-site (e.g., placing a relay antenna or pocket Wi-Fi at a high location). If correction data cannot be obtained, it may be necessary to suspend the survey temporarily and wait for communication recovery or switch to using your own base station. Additionally, be aware of potential issues with correction data formats. Depending on the Ntrip connection, there may be differences in RTCM message versions or coordinate systems, and the terminal may not be able to apply corrections correctly if it doesn’t support the information. While most Japanese electronic reference points provide data in RTCM3.x format, compatibility issues may arise with overseas base stations or older equipment. In such cases, switching to another service or contacting LRTK’s support team to verify the proper settings is recommended.

• Handling of the Terminal and App:
  Both the LRTK terminal and smartphone are precision instruments. Be cautious of dropping, shock, or water damage during field operations. While the LRTK terminal is designed to be durable, if the smartphone is not waterproof, use a waterproof case in case of rain. If the app behaves unexpectedly during surveying (e.g., GPS information stops updating or freezes), try restarting the app or rebooting the smartphone. If this doesn’t resolve the issue, re-pair the terminal with the smartphone (reconnect via Bluetooth). If you experience an unexpected device malfunction in the field, remain calm and troubleshoot the cause step-by-step. It’s always a good idea to have a spare smartphone and backup batteries for added peace of mind.

• Preventing Surveying Errors:
  Be mindful of human errors, such as mixing up point names or numbers, or mistakenly saving measurements of one point under the wrong name. While the LRTK app automatically assigns serial numbers, it’s a good practice to manually name important points or take photos and link them to the points to avoid confusion when reviewing the data later. Another common error is forgetting to press the record button, resulting in missing data. After surveying, it’s essential to verify the number and content of the recorded data on-site and ensure there are no missing or incorrect entries by following a checklist.

• Regular Accuracy Verification and Calibration:
  For long-duration work, it’s advisable to periodically re-measure known points to check accuracy. Satellite configurations may change between the morning and afternoon, and weather conditions (e.g., ionosphere status) may affect the measurements, potentially causing slight positioning bias. By periodically measuring reference points and confirming there are no discrepancies with the initial values, you can ensure the reliability of your surveying. If needed, apply coordinate offset corrections in the app (if available) to maintain data consistency.

By keeping these precautions in mind, RTK surveying with the LRTK terminal can be conducted with great stability. If problems arise, calmly identify the cause and take prompt action to address the issue before it becomes serious. Even with the latest equipment, it is still fundamentally a surveying task, so prioritize safety and be mindful of the surrounding work conditions as you proceed.