RTK Utilization Tips from Surveyors:
How to Streamline Civil Engineering Surveying

What is RTK Surveying? Basic Knowledge and Differences from Traditional Surveying
RTK surveying is a positioning method that uses two GNSS receivers, a base station and a rover, to correct positioning errors in real-time. The base station is set up at a known coordinate point, and the rover is used at the location to be surveyed. Both receivers simultaneously receive GNSS signals from satellites, and the base station sends the calculated error correction information to the rover via radio. This allows the rover to obtain high-precision coordinates, with the satellite positioning errors corrected.

When compared to traditional surveying using a total station (TS), there are several significant differences in RTK surveying. First, in terms of personnel, TS surveying typically requires two people: one to operate the surveying equipment and the other to hold the prism. However, RTK surveying, using GNSS, can generally be done by a single person.

Additionally, ensuring line-of-sight is essential in TS surveying, and if there are obstacles between the survey points, equipment must be repositioned or relay points are needed. However, RTK surveying only requires the ability to receive signals from satellites, so line-of-sight between points is not necessary. Moreover, measurement time is also reduced. In TS, measuring the coordinates of a single point involves setup, aligning the equipment, targeting the prism, and taking readings. In RTK, the rover's position is simply recorded at the desired point, completing the coordinate acquisition. In practice, RTK surveying can take as little as "10 seconds per point," enabling efficient measurement of multiple points.

In terms of accuracy, TS provides extremely high precision, with millimeter-level accuracy over short distances. However, when surveying large areas, the need to reposition the equipment repeatedly results in accumulated errors, which is a challenge.

On the other hand, RTK surveying always calculates the coordinates of each point relative to the same base station, preventing error propagation between survey points and maintaining stable accuracy. RTK-GNSS receivers achieve centimeter-level positioning accuracy in horizontal positions, meeting the precision typically required for civil engineering surveying. Overall, RTK surveying is an efficient method that covers large areas with a small team in a short amount of time, while providing sufficiently high accuracy for most surveying tasks.

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The Importance of Utilizing RTK in Civil Engineering Surveying

In the context of national resilience, infrastructure maintenance, and the ongoing trend of construction digital transformation (i-Construction), civil engineering surveying is increasingly required to balance speed and accuracy. The use of RTK surveying is essential to meet these needs.

First, from the perspective of improving surveying accuracy, the introduction of RTK is highly significant. For example, in the maintenance of railways and highways, even a few centimeters of misalignment can impact the management of structures. With RTK, GNSS positioning errors can be reduced to within a few centimeters, allowing for more accurate assessments of the current status and as-built management of critical infrastructure using its high precision.

Additionally, RTK-GNSS enables large-scale 3D measurements that were previously difficult. Combined with drone aerial photography or ground-based laser scanning, RTK is helpful in providing positioning references (coordinates) for large-scale point cloud data.

By using RTK, a large number of points over a wide area can be measured in a short amount of time, with coordinates obtained to within a few centimeters of accuracy. Compared to traditional total stations, this significantly improves work efficiency and makes high-precision 3D surveying much easier.

Next, regarding improving operational efficiency: In the construction industry, where labor shortages are a serious issue, utilizing RTK is key to completing surveying tasks with limited personnel. With RTK surveying, one person can perform the surveying work, allowing for significant reductions in personnel.

For example, even small-to-medium-sized civil contractors can benefit, as surveyors can complete on-site surveying alone, freeing up time for other tasks. Additionally, by using network-based RTK services (such as the VRS method), there is no need to set up your own base station, reducing the effort needed to prepare equipment. In a case study where network-based RTK was implemented, it was reported that "no base station setup was required," and "only one GNSS receiver was needed," resulting in benchmark surveying work that previously required two trips (one for the total station and one for leveling) being completed in a single round (leveling + GNSS observation). This reduction in work time is a huge benefit, even in extreme weather conditions like intense heat or cold. Moreover, because "line-of-sight is not required," the flexibility of the surveying area increases, allowing for broader coverage without being hindered by obstacles. This leads to improved productivity, reduced errors, and low-cost results.

In this way, the use of RTK can be described as a revolution in civil engineering surveying, simultaneously enhancing both accuracy and efficiency.

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RTK Utilization Tips from Surveyors (Tips for Improving Accuracy, Equipment Setup & Operation Points)

To fully maximize the benefits of RTK surveying, it is essential to understand a few tips and key points. In this section, experienced surveyors will share the RTK utilization points they’ve developed on-site, divided into "Tips for Improving Accuracy," "Equipment Setup and Operation Points," and "Important Considerations to Avoid Mistakes."

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Tips for Improving Accuracy

• Ensuring Clear Sky Visibility:
  In RTK surveying, it is essential to receive satellite signals stably. Both the base station and the rover should have antennas set up in open areas where the surroundings are visible, ensuring a clear view of the sky. RTK surveying is especially effective in environments with no obstructions overhead, such as large airport areas. Conversely, in places under the shadow of buildings or trees, the number of visible satellites decreases and the error increases, so it’s necessary to either avoid these areas or adjust the observation time accordingly.

• Multipath Error Mitigation:
  Be cautious of multipath errors, which occur when satellite signals are reflected off surfaces such as metal fences or building walls. This causes direct and reflected waves to mix, leading to a disruption in positioning accuracy. To prevent this, place the antenna as far from reflective surfaces as possible, and, if necessary, raise the antenna height (e.g., use a taller pole). Even high-sensitivity receivers cannot perform well in multipath environments. Before starting the survey, check the satellite configuration map and DOP values, and avoid locations and times that may negatively affect accuracy.

• Ensuring Sufficient Satellite Count:
  For RTK to consistently obtain a fix, it is generally recommended to track at least four GNSS satellites simultaneously, and preferably six or more. In Japan, multi-GNSS receivers that track satellites such as GPS, GLONASS, and Michibiki (QZSS) are common. Ensure that the required satellite groups are enabled in the receiver settings. If using a receiver that supports the centimeter-level correction service (CLAS) from Michibiki, it is also important to consider the line of sight to the southeast direction, where the geostationary Michibiki satellite is visible.

• Setting Up the Base Station at Known Points:
  The base station should be set up at a point with known accurate coordinates, or at a location where the position has been precisely determined through extended observation. If the accuracy of the base station’s position is low, the same amount of error will affect all survey points, so this needs careful attention. If there is no known point available on-site, consider using public reference points for setup or use network-based RTK services to omit the need for a base station. If setting up the base station without a known point, remember that later you will need to perform a "localization (shift)" operation to correct the base station’s coordinate error in the rover’s observation data.

• Antenna Height and Leveling:
  It’s essential to accurately measure and input the antenna height (from the antenna reference point to the ground) for both the base station and the rover. Mistakes in setting the antenna height directly lead to errors in the vertical direction, so check it carefully. While recent receivers may have built-in electronic leveling or tilt correction functions, it’s still best practice to ensure that the antenna (or pole) is kept vertical during surveying. Especially in cases where the receiver does not support tilt correction, any tilt in the pole will cause errors. Always check the bubble level on the leveling device and maintain vertical alignment during observations.

Installation and Operation Points

• Stable Installation of the Base Station:
  The GNSS antenna on the base station should be securely fixed with a tripod or similar device to prevent it from moving or falling. In areas with strong winds, placing weights on the tripod or lowering its height can help improve stability. To ensure accurate placement on the reference point, use a leveling plate or a plumb rod to set the antenna directly above the point and adjust the horizontal alignment with a spirit level. Be mindful of potential battery depletion during long continuous observations and always prepare backup power sources or generators.

• Check the Communication Environment:
  For transmitting real-time correction information, radios or mobile phone networks are used. If the mobile signal is weak on-site, network-based RTK may suffer from communication interruptions, which could decrease accuracy. Check the communication environment in advance, and if necessary, use high-gain antennas or repeaters, and position the base station and rover in locations with a clear line of sight. When using radios, ensure compliance with radio laws and be aware of potential frequency interference with other equipment.

• Regular Accuracy Checks:
  During RTK observations, it is essential to develop the habit of performing accuracy checks at regular intervals, using known points or overlapping observation points. Verify whether the obtained coordinates match known values, or check if there is no variation when measuring the same point multiple times. If a significant discrepancy occurs, consider discarding the data for that period and re-measuring. If the signal reception quality worsens, there is a risk that the solution could switch to "floating" (unresolved integer ambiguity), leading to erroneous measurements. Always monitor the solution status to ensure you have a "FIX" solution and avoid mistakenly registering points while still in "FLOAT" mode.

• Use of GNSS and Other Surveying Equipment:
  There are situations where RTK-GNSS may not perform well. For example, in projects with strict elevation requirements, GNSS’s vertical accuracy (typically about twice the error of horizontal position accuracy) may not be sufficient. In such cases, it is important to combine RTK with leveling for critical elevation measurements, or use a total station for detailed surveys in confined areas. Cross-checking coordinates obtained from GNSS with those obtained using other methods can help prevent mistakes by confirming there are no significant discrepancies.​

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Important Considerations to Avoid Mistakes

• Dealing with Loss of Signal:
  In areas like mountainous regions or under viaducts, where GNSS signals are prone to interruption, RTK positioning may not be possible in the worst-case scenario. To prepare for such situations, it is advisable to plan for reference point setup or traverse surveying in advance. Especially in infrastructure inspections, such as for railways or highways, when surveying along linear routes, if GNSS cannot be used in tunnels or under viaducts, it's necessary to combine RTK results with other survey methods (such as alignment surveying) to cover these areas. Don’t rely solely on "RTK"—always have an alternative plan ready.

• Bad Weather and Ionospheric Effects:
  During heavy rain or snowfall, GNSS signals can be attenuated, leading to a decrease in accuracy. Additionally, when ionospheric disturbances are significant, such as during solar flares, positioning errors can increase. If bad weather is expected on the scheduled survey day, try to reschedule if possible. If rescheduling is difficult, increase the measurement interval or use averaging features to stabilize accuracy. Keep in mind that GNSS signal conditions are never constant, so it's essential to plan a schedule with some flexibility.

• Keeping Up with the Latest Information:
  Technological advancements in GNSS and RTK are progressing rapidly. As a surveyor, it's important to stay informed about the latest developments, including firmware updates and the use of new services. For example, public services such as correction data from Japan’s Quasi-Zenith Satellite System (QZSS), including CLAS and MADOCA-PPP, are becoming more advanced. By using these services, centimeter-level positioning can be achieved without the need for a base station. Manufacturers are also releasing new products and features, so be sure to catch up regularly to make the most of these advancements for your surveying operations.

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How RTK Utilization Can Streamline Surveying Operations

By properly utilizing RTK surveying, the productivity of civil engineering surveying can be dramatically improved. Let’s review the benefits that RTK brings to surveying operations in terms of efficiency.

• Survey Large Areas with Fewer People:
  With RTK, a single person can perform the surveying, making it possible to handle sites with labor shortages. Traditional surveying, which required two people, can now be done as a one-person task, allowing the second person to focus on other tasks. This leads to reduced labor costs and more flexible scheduling. In fact, a surveying company that introduced RTK reported that the burden on their surveyors was greatly reduced, describing their experience as "no need for line-of-sight, 10 seconds per point, and all done by one person."

• Shortening Equipment Setup and Movement Time:
  In total station surveying, every time the line of sight is obstructed, the equipment needs to be repositioned, and back-sight measurements are required. In large areas, this means moving the tripod multiple times, which can be time-consuming. With RTK, once the base station is set up, the rover can freely move around and take measurements, eliminating the need to repeatedly set up heavy equipment. Using network-based RTK eliminates the need to set up a base station entirely, enabling surveying to start immediately upon arrival at the site. For example, traditional methods of benchmark surveying, which took "one round trip with TS and one round trip with leveling," can now be completed with just "one round trip with leveling and GNSS observation" using RTK, drastically reducing the time required.

• Immediate High-Precision Data Acquisition:
  RTK surveying, with real-time corrections, allows for high-precision coordinates to be obtained on-site immediately. There is no need to spend time processing data at the office or waiting for post-processed GPS (PPK) results. Surveyors can review the observed results immediately on-site, allowing them to quickly identify and address any missed measurements or errors. This directly contributes to reducing delays and errors. Additionally, the obtained coordinates can be used directly in public coordinate systems (such as the World Geodetic System, or JGD2011/JGD2020 in Japan), making it easy to align with design drawings and GIS data. This streamlines subsequent design and construction management processes.

• Improved Safety:
  Shortening surveying time also helps reduce the risk of accidents on-site. For surveying tasks on highways or along railways, it is best to finish as quickly as possible to minimize exposure to dangerous areas. By completing tasks quickly with RTK surveying, workers can spend less time in hazardous zones. Moreover, tasks that can be done alone avoid crowded work environments, reducing the risk of contact in areas where heavy machinery is in use.

As shown, by utilizing RTK, surveying becomes "easier and faster." This is not just about efficiency—it also contributes to the workstyle reforms being demanded today, such as reducing overtime and improving safety management. For general contractors and civil engineering companies that have not yet adopted RTK, this is an excellent opportunity to consider adopting the technology.

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How to Utilize the Latest RTK Technology "LRTK" for Even Easier and More Accurate Surveying

One of the latest trends in RTK technology is the solution called LRTK, developed by Lefixea Inc., a venture startup from Tokyo Institute of Technology. Traditionally, RTK equipment was stationary or pole-mounted, but LRTK is revolutionary in that it allows for easy centimeter-level positioning by integrating with a smartphone. The representative device is the LRTK Phone, an ultra-compact RTK-GNSS receiver that attaches to mobile devices like iPhones and iPads.

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With the LRTK Phone, the smartphone transforms into a high-precision surveying tool. By simply attaching the dedicated device (black housing) to an iPhone, you can use it as a handheld RTK surveying device. It’s portable and allows for immediate surveying when needed, making it incredibly convenient. The LRTK Phone device, shown in the picture, is integrated with a small antenna and battery on the back of the smartphone.

Simply attach the LRTK Phone to your smartphone and launch the dedicated app to easily perform RTK surveying using satellite-based relative positioning. What used to require specialized surveying equipment for centimeter-level positioning can now be achieved with a smartphone—truly an example of "one device per person." For example, in concrete structure crack surveys, you can easily tag the accurate coordinates of the location to photos taken with your smartphone and save them to the cloud.

Tasks that once required paper and measuring tapes for note-taking are now digitized, dramatically improving both the efficiency and accuracy of surveys.

The LRTK Phone has other advantages as well. Despite weighing only 125g and having a thickness of 13mm—compact enough to fit in your pocket—it runs on an integrated battery and transmits position data in real-time to the smartphone via Bluetooth. The coordinates obtained are global coordinates using the World Geodetic System, with centimeter-level precision. This small device can perform surveying, point cloud measurement (photogrammetry), stakeout, and even overlaying AR data, all in one device. Moreover, it is significantly more affordable than traditional surveying equipment, making it practical for each field worker to have their own device. In fact, sites that have adopted LRTK report that "everyone can easily perform high-precision surveying," significantly improving on-site productivity.

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Furthermore, the LRTK series includes various devices tailored to on-site needs. For example, the LRTK Pro2 is a compact, lightweight RTK device designed for professional use, integrating the antenna, GNSS receiver, battery, and radio into one unit. It is dustproof, waterproof, and shock-resistant, making it suitable for harsh construction environments. A notable feature is its compatibility with Japan's Quasi-Zenith Satellite System (QZSS) CLAS, allowing for high-precision positioning even in remote mountainous areas with no internet access, relying solely on satellite correction signals.

In addition, the built-in tilt correction feature allows for accurate measurements even if the pole is slightly tilted. This is particularly useful in areas with overhead obstacles, allowing for effective surveying even when the pole is held at an angle. It’s compatible with smartphones and tablets, enabling quick and flexible surveying that offers far superior mobility compared to traditional fixed RTK equipment.

A unique product in the LRTK lineup is the LRTK Helmet, where a thin antenna-equipped receiver is mounted on a worker’s helmet, allowing continuous surveying simply by walking. Even if the worker’s hands are occupied, positioning can still be performed, making it useful for tracking the worker's movements and continuous surveying along a line. With an internal battery that lasts up to 12 hours, the collected data is transmitted in real-time to the cloud via the smartphone, allowing for immediate progress checks and instructions from remote offices. In this way, LRTK enables innovative RTK use, breaking away from traditional surveying methods.

By incorporating the latest technologies like LRTK, civil engineering surveying can become even more efficient and advanced. For small-to-medium-sized contractors and infrastructure maintenance professionals, the ability to perform high-precision surveying using just a smartphone, instead of relying on expensive specialized equipment, is an invaluable advantage. As technologies like LRTK continue to spread, the way surveyors work will likely undergo significant changes.