What Is Control-Point Surveying?
A control point is a location on the Earth whose position—latitude, longitude, and elevation—has been precisely determined. Examples include triangulation stations, leveling benchmarks, and permanent GNSS reference stations. These points serve as the foundation for map creation and all types of surveying​. Control-point surveying is the process of establishing or verifying the coordinates of these reference points, and it is used in a wide range of applications, from building design and road planning to land boundary investigations and infrastructure maintenance​.

For example, in civil engineering projects, establishing control points first allows all subsequent surveying and construction to reference the same set of coordinates, preventing discrepancies between different work stages. The high‐accuracy data obtained from control‐point surveys play a critical role in determining the overall success of the project.

When establishing new control points, it’s essential to minimize sources of error as much as possible. In practice, this means choosing a location with a clear, unobstructed view of the sky; mounting the receiver on a sturdy, well‐secured tripod or pole; and ensuring the unit cannot move during measurement. It’s also important to link your new control points to existing reference networks—such as public GNSS stations or national coordinate systems. In areas with multiple control points, leveraging a network‐RTK solution can help maintain correction accuracy over long baselines, since multiple base stations mitigate precision loss even at greater distances.

Using RTK for control‐point surveys offers significant advantages over traditional methods: it is both faster and more precise. Because positions are fixed in real time, there is no need for post‐processing, and you can verify results on the spot. In particular, by tapping into a network‐RTK correction service via NTRIP, users can achieve centimeter‐level accuracy over long distances without deploying their own base station—dramatically reducing field setup time. In this way, RTK empowers highly efficient, high‐precision control‐point surveying.

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Procedure for Control-Point Surveying with LRTK
Now, let’s walk through a typical workflow for conducting a control-point survey using LRTK. We’ll focus on operating your own LRTK receivers in base-station and rover modes, and also cover how to incorporate a network-RTK correction service when needed.

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Equipment Preparation and Configuration
Begin by preparing your surveying equipment. Retrieve the LRTK receiver and verify that its battery is fully charged. The LRTK is a small, disc-shaped device—small enough to fit in the palm of your hand. Securely mount it to your survey pole or tripod, and use a level to ensure the pole or tripod is perfectly vertical (the LRTK Pro series features a flat base with a mounting interface for stable setup).

Next, launch the LRTK app on your smartphone or tablet and pair it with the receiver via Bluetooth. Once the app recognizes the device, configure your positioning mode and coordinate system. If you’re working in Japan and need to use the public coordinate system, select the appropriate plane-rectangular coordinate zone (by region code) and geodetic datum (e.g., JGD2011). If you already have known control-point coordinates—such as a nearby official triangulation station—enter those values now to use as your reference. After completing these settings, you’ll be ready to switch the unit between base-station mode and rover mode.

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Base Station Setup and Configuration
In control‐point surveying, the base‐station receiver should ideally be installed over a known point. A known point is one whose coordinates (latitude, longitude, and elevation) have already been precisely determined—such as a permanent GNSS reference station, a triangulation station, or an existing site control point from a previous survey. Mount the LRTK receiver on that point and register its fixed coordinates in the app. This lets the base station know its exact position and generate correction data accordingly.

In the LRTK app on the base‐station unit, switch to Base Mode and begin broadcasting correction information. When using multiple LRTK Pro receivers, you can also employ the proprietary “L-Link” communication over the 920 MHz license-exempt band to broadcast corrections. With L-Link, a single base station can simultaneously transmit correction data to multiple rovers—ideal for teams of surveyors working concurrently in the field.

On the other hand, if there are no known control points on site or you choose not to deploy your own base station, you can use an internet-based NTRIP service. In the LRTK app settings, enable the NTRIP client and enter your subscribed network-RTK correction service details (connection URL, login ID/password, etc.). Once connected, correction data (RTCM) is automatically retrieved from the surrounding permanent GNSS reference-station network. In this mode, the LRTK receiver functions as a rover, using a network RTK base station—including Virtual Reference Stations (VRS)—to perform positioning.

In summary, there are two ways to configure the base station:

• Using Your Own Base Station: Install the LRTK receiver at a point with known coordinates, switch to Base Mode, and begin broadcasting correction data—either over radio link (e.g., L-Link) or via an NTRIP server.

• Using a Network Base Station: Operate the LRTK as a rover by enabling the NTRIP client to receive correction data from the public reference‐station network.

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In either case, after configuring the base station, wait for several tens of seconds to ensure that correction data is being output stably. On the base‐station LRTK unit, check the LED indicators or app display for satellite lock count and correction‐data transmission status. If everything is normal, proceed with the rover operations.

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Rover Setup
Next, configure the rover. Prepare a second LRTK receiver (or a smartphone fitted with an LRTK Phone) as your rover, and carry it to each survey point. In the LRTK app on the rover device, switch to Rover Mode so it’s ready to receive correction data. If you’re using your own base station, connect the rover to the base station’s radio link or NTRIP stream. Once the rover and base station are paired and the correction data (RTCM) arrives, the app will display the RTK solution status on screen.

By receiving the correction data, the rover calculates the difference between its raw GNSS observations and the corrections to derive a high-precision position with error sources removed​. At this stage, the RTK solution status is critical. When the rover’s status reads Fix, it means centimeter-level accuracy has been achieved​. If it remains Float or Single, the errors are still too large, so you must wait until a Fix solution is obtained. Under good satellite visibility and stable base-to-rover communication, convergence to Fix typically occurs within tens of seconds to a few minutes.

It’s also important to enable the control-point survey (static) mode on the rover. In the LRTK app, you can switch from a single-shot measurement to an “averaged positioning” mode, where the receiver continuously records for a set period and computes the mean coordinate​. In applications like control-point surveys—where the highest precision is required—turning on averaging and using the mean of multiple observations yields more stable results. For example, one test using the LRTK app averaged over 60 seconds reduced the horizontal position’s standard deviation from 12 mm (single-shot) down to 8 mm​. You can adjust the measurement interval and averaging duration as needed to suit your accuracy requirements.

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Conducting the Survey
Now you’re ready to measure your control point. Position the rover—either the standalone LRTK receiver or a smartphone fitted with the LRTK Phone—directly over the point you wish to survey. For a newly established control mark, place the tip of your survey pole or the receiver’s phase center exactly above the mark on the ground. If you’re using a tripod, ensure the leveling head sits precisely over the point and adjust the height accordingly.

Once setup is complete, start the survey in the app and wait until the RTK solution status shows a stable Fix. To reduce the effects of equipment noise or minor environmental changes, you may take dozens of measurements at that one point and let the app compute the average coordinate. When you confirm that your accuracy meets requirements—e.g., horizontal error consistently under 1 cm—record the measured coordinate for that control point.

In the LRTK app, you can review detailed information for each measured point—date and time, latitude/longitude, plane‐rectangular coordinates, geoid height, positioning mode, and more. At this stage, always verify your positioning accuracy by examining HDOP/PDOP values (indicators of positional precision), the stability of the Fix solution, and the estimated error in each axis, all displayed in the app. If everything looks good, enter a point name and any notes, then save the measurement (as shown in the left screenshot, where you can add a title and memo). Data recorded in the LRTK app can also be synchronized to the “LRTK Cloud” service, allowing you to view positions later on a web map from your PC or share them with project stakeholders​.

If there are multiple control points, repeat the above procedure at each location. For each new control point, verify the measurement error relative to the reference known point and its consistency with the other control points, performing any re-measurements or adjustments as necessary. Once all control points have been measured, the on-site control-point survey is complete.

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Practical Guide to Control-Point Surveying
To ensure a successful, high-precision control-point survey, we’ve compiled key tips, precautions, and troubleshooting strategies for the field. Use the following guidelines to maintain survey accuracy and keep your workflow running smoothly.

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Keys to Measuring Accurate Control Points

• Choosing the Right Location: Select a spot with an unobstructed view of the sky and without nearby tall buildings or trees. The more open the sky above your point, the more stable your GNSS signal reception and positioning accuracy will be. In environments prone to multipath errors—such as urban canyons or dense forests—consider relocating the point to a clearer area or temporarily raising the antenna on an extension pole to minimize reflections and blockages.

• Stable Equipment Setup: Securely fasten the receiver to your tripod or pole so that it cannot move or tilt during measurement. When using a tripod, spread the legs fully, set them firmly on solid ground, and tighten the leg‐lock screws for maximum stability. If you’re using a pole, anchor its base or have an assistant hold it steady to prevent any movement. Models like the LRTK Pro2 include tilt‐compensation, which corrects for slight pole inclinations internally, but for control‐point surveying it’s best to keep the pole as vertical as possible.Also, accurately measure the antenna height—the distance from the ground to the antenna’s phase center—and enter that value precisely into the app. Any error in the antenna‐height input will directly translate into elevation error, so take care to record it correctly.

• Sufficient Observation Time and Averaging: To improve accuracy, perform multiple observations at the same point and average the results. Even if time is limited, maintain a stable Fix solution for at least 1–2 minutes and use the data collected during that period. By using the LRTK app’s averaging function, you’ll automatically receive statistically processed coordinates​. Recording in a stationary position over an extended period helps smooth out transient errors caused by ionospheric disturbances or uneven satellite geometry. If possible, repeat the measurement after a short interval and compare the results—this further enhances reliability.

• Cross-Checking: In control-point surveys, it’s crucial to cross-check your GNSS-derived coordinates against other methods or existing known points. For example, you could later measure the distance between two newly established control points with a tape measure or total station and compare it to the distance calculated from their GNSS coordinates. If coordinates for nearby public reference stations are available, survey from your new control point to one of those known points and check the error. Verifying results with multiple surveying methods helps uncover unexpected mistakes or systematic errors.

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How to Verify Measurement Results

• Real-Time Accuracy Check: While surveying, monitor the app’s display for the solution type (Fix/Float/Single) and the estimated error values. Make sure the Fix solution is being maintained and that indicators like HDOP remain within acceptable limits. If you’re not achieving the required accuracy, consider extending your observation time or improving the environment—for example, repositioning yourself so the antenna has a clearer view of the sky.

• Post-Survey Data Verification: Always record your saved control-point coordinates in your field notes or survey notebook. Once back in the office, you can review the synced data from LRTK Cloud on your PC. In the cloud interface, each surveyed point is plotted on a map, and you can view a table of point names, timestamps, coordinates, and any notes. Use this to check for omissions or transcription errors in your field measurements. Additionally, if needed, reconfirm any transformations to other coordinate systems or the application of geoid heights (even though the LRTK app automatically performs plane-rectangular coordinate conversions and geoid-height computations, it’s prudent to verify them).

• Accuracy Assessment: When you’ve established multiple control points, evaluate their relative accuracy. For example, calculate the distances and angles between your newly placed control points and compare them against design values or existing reference data. If they match, you’re all set. If you notice slight discrepancies, determine whether they fall within your expected measurement error range. As needed, you can re-survey points, use averaged values, or remove outliers to adjust the data. Finally, when you compile your control-point survey results into a report or deliverable, explicitly state the achieved accuracy level—doing so will enhance the credibility of your work.

• Data Storage and Utilization: The control-point coordinates you establish may be used for future construction or surveying projects over many years. Back up the electronic data in your internal survey database or on the cloud, and also document the results tables or plans in hard-copy for archival. Using LRTK Cloud makes it easy to share the published point data both inside and outside your organization. By maintaining thorough data management, you can reuse these control points in subsequent projects—saving time and reducing costs.

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Control‐Point Survey Troubleshooting

• RTK Won’t Achieve a Fix: If you have few satellites in view or poor signal conditions, the RTK solution may remain in Float or Single mode. In that case, scan your surroundings to ensure nothing is blocking the sky above the receiver. Try moving the receiver a few meters or temporarily mounting it higher to improve reception.Also verify that correction data from the base station is actually reaching the rover. In the app, check the correction‐data status—if using NTRIP, confirm your mobile network signal strength; if using a radio link, ensure adequate line‐of‐sight and range.If you still can’t get a Fix, reset the survey solution (for example, by restarting the app) and try again. Failing that, consider changing the survey time to a period with better satellite geometry (lower GDOP) for improved chances of achieving a Fix.

• Unable to Receive Correction Data: If your NTRIP connection fails, first check your mobile network. In tunnels or mountainous areas, a weak cell signal may force you to move to a spot with better coverage. Also re-verify your credentials—ensure your caster URL, mount point, user ID, and password are entered correctly.If you’re using a model like the LRTK Pro2 that supports QZSS’s CLAS service, you can receive centimeter-level corrections directly from the Michibiki satellites even outside mobile coverage​.Conversely, if you’re running your own base station and the rover cannot pick up the radio link, verify that you’re not too far from the base and that no obstacles block the line of sight. You might relocate the base station to higher ground or switch the rover to NTRIP over the internet as an alternative.

• Apparent Shift or Error in Positioning Results: If the coordinates you obtain differ significantly from known values, several causes may be at play. First, check for a mismatch in reference frames—confirm whether you’re using Japan’s geodetic system (JGD2011) versus the global WGS-84, and whether geoid-height corrections have been applied to your elevations. Although the LRTK app performs these conversions automatically, inconsistencies can arise when exchanging data with external devices or third-party software.Next, verify that the base-station coordinates themselves were entered correctly. A single misplaced digit or swapping east longitude for north latitude will shift every measurement by the same amount. In such cases, correct the base-station coordinates and re-measure with the rover.Physical factors can also introduce errors: someone may have bumped the receiver during measurement, or a passing vehicle or person may have temporarily interfered with the signal. Always keep the work area clear and avoid touching or disturbing the receiver while it’s collecting data.

• Mitigating Equipment Failures: Prepare for battery depletion and potential device malfunctions. Ensure both the LRTK receiver and your smartphone are fully charged before a long day of surveying, and carry spare batteries or a portable power bank for peace of mind. If the app unexpectedly quits, jot down any critical point measurements immediately so you can restore them after restarting. Keep the receiver’s firmware and the app updated to the latest versions to avoid known bugs. If you encounter an issue you can’t resolve on site, don’t hesitate to pack up and inspect your equipment—it's better to pause and return another day than to continue collecting faulty data and compromise your accuracy.

 

Utilization and Benefits of Implementing LRTK
Finally, let’s summarize the advantages and real-world applications of adopting LRTK. While offering all the core performance you expect from an RTK GNSS receiver, LRTK also incorporates numerous field-friendly features throughout its design—making it an exceptionally useful tool for surveying operations in the construction and infrastructure sectors.

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✔ Compact, Lightweight, and Highly Portable: The LRTK series combines receiver, antenna, and battery into a single, compact unit. For example, the disc-shaped LRTK Pro weighs just 280 g and measures about 10 cm in diameter—small enough to fit in the palm of your hand—and can be mounted easily on a pole or tripod. The smartphone-mounted LRTK Phone is even smaller, at only 125 g and 13 mm thick, so it slips into your pocket with no hassle. With such minimal bulk, one person can carry multiple units around the site effortlessly.

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✔ Easy Operation—Accessible to Anyone: The dedicated LRTK app offers an intuitive user interface, letting you start and stop positioning, save data, switch coordinate systems, and more with the tap of a button. It automatically converts results into Japan’s plane rectangular coordinates and geoid height, so you don’t need to do any manual calculations. You can name points and add notes on the spot—no paper field books required. Cloud integration enables seamless data sharing, instantly relaying results from the field to the office. With only a brief training session, even non-specialist operators can run surveys on their own device, making decentralized, on-the-go surveying a reality.

✔ High-Precision, Highly Reliable Positioning: LRTK employs cutting-edge GNSS modules with multi-constellation and multi-frequency support, delivering outstanding accuracy. It provides real-time, centimeter-level RTK positioning, and by averaging measurements you can push precision toward the millimeter range. The flagship LRTK Pro2 adds tilt-compensation, so you still get accurate results even if your survey pole is slightly off-vertical. Plus, with IP-rated dust- and water-resistance and ruggedized design, it stands up to the toughest outdoor environments.

✔ Diverse Communication Options and Correction Sources: In addition to Bluetooth and USB connectivity, the LRTK Pro/Pro2 models feature a built-in proprietary low-power radio link (L-Link), allowing simultaneous correction broadcasts to multiple rovers even outside of cellular coverage. Moreover, the LRTK Pro2 can receive the QZSS “Michibiki” centimeter-class augmentation service (CLAS), so it can pull down correction data via satellite in remote, mountainous areas without mobile signal. This ability to flexibly choose both communication method and correction source for each use case is a major advantage.

✔ Implementation Costs and Case Studies: Compared to traditional survey-grade GNSS receivers, the LRTK is priced very affordably, lowering the cost barrier. This makes a “one-device-per-person” deployment realistic, and we’re already seeing examples of site supervisors and field crews each carrying an LRTK to boost their work efficiency.

For example, on highway infrastructure inspections, teams have used the LRTK to rapidly establish control points on bridges, streamlining subsequent 3D measurements. In railway maintenance, operators have completed solo surveys in the tight space alongside tracks using the LRTK Phone, helping to shorten nighttime work windows. And in the aftermath of the 2023 Noto Peninsula earthquake, the LRTK Pro2’s ability to receive CLAS augmentation in mountainous, off-grid areas proved invaluable for on-site investigations.

Thus, LRTK is attracting attention not only in civil engineering and construction but also as a tool supporting the digital transformation (DX) of disaster prevention and surveying operations.