Table of Contents

• What is RTK-GNSS? Its positioning principles and variations

• Differences between each approach and comparison points (accuracy, cost, environmental constraints, ease of implementation)

• Background and advantages of smartphone RTK surveying

• Main functions of LRTK systems (AR guidance, point cloud scanning, cloud sharing, photogrammetry, etc.)

• Business transformations enabled by smartphone RTK (reduced labor, time savings, remote support, as-built management, etc.)

• Field implementation cases and effects (efficiency differences compared to conventional methods)

• Advice for those considering adoption (selection points, cautions, initial implementation steps)

• Guidance for introducing LRTK to simple surveying

• FAQ

Smartphone-based RTK surveying combining smartphones with GNSS technology, known as smartphone RTK surveying, is attracting significant attention on construction and civil engineering sites. Centimeter-level, high-precision positioning via RTK-GNSS has become easily accessible to anyone, enabling intuitive work support through AR displays and even point-cloud scanning using LiDAR. With labor shortages intensifying, "surveying that can be done by a single person" and "measurements that can be shared in real time" are solutions that directly improve on-site productivity. In this article, we explain the basics of RTK-GNSS and compare differences among its methods, detail the advantages smartphone RTK brings and concrete use cases, and cover the functions and implementation points of the innovative smartphone surveying device LRTK. Finally, we answer questions in an FAQ format, so please take the opportunity to understand the potential of smartphone surveying.

What is RTK-GNSS? Its positioning principles and variations

First, GNSS refers collectively to multiple satellite positioning systems such as GPS (U.S.), GLONASS (Russia), Galileo (Europe), and Michibiki (Japan's quasi-zenith satellite). A GNSS receiver receives radio signals from multiple satellites and calculates the current position (latitude, longitude, altitude) from the distance information to each satellite. However, with ordinary standalone positioning, errors in radio propagation and the like mean position accuracy remains on the order of several meters. Typical smartphone GPS also has errors of about 5–10 m, which is not sufficient for precise surveying.

A method to correct these errors and achieve centimeter-level positioning accuracy is RTK (Real-Time Kinematic) positioning. In RTK, both a base station (a receiver installed at a known precise position) and a rover (a portable receiver) simultaneously receive GNSS signals. The base station calculates the discrepancy between its true precise position and the positioning result, and sends that correction data to the rover in real time. The rover receives the correction information and applies the error corrections to its own positioning data, allowing positions that were typically off by several meters to be improved to an accuracy within a few centimeters. This is possible because it uses precise ranging signals called the carrier phase of the satellite signal, which can detect distance differences down to the millimeter level. With the advent of RTK, real-time high-precision positioning has become practical across a wide range of fields such as civil surveying, agriculture, and autonomous driving.

RTK-GNSS has several configurations depending on the mode of operation, each with its own characteristics. The three representative variations are the following:

• Conventional RTK (standalone): The user themselves installs a dedicated base station near the site, and sends correction information to the rover via radio. It's a simple one-to-one setup that provides high accuracy, but it requires the effort of setting up the base station each time, and accuracy decreases as you move away from the base station. In general, when more than 10 km away from the base station, correcting errors becomes difficult. Also, the cost of purchasing dedicated equipment and the need for specialized operational knowledge meant the adoption barrier was relatively high.

• Network RTK: It uses multiple reference station networks and obtains correction data via the Internet. A typical example is the VRS (Virtual Reference Station) method, which assumes a virtual reference station near the user's position and delivers correction information. Because you can receive correction information via communication infrastructure such as mobile networks, there is no need to set up your own base station, and you can start positioning immediately anywhere. Even when moving across a wide area, corrections from nearby virtual reference stations are always available, suppressing accuracy degradation due to distance. However, a subscription to the correction service (monthly fees, etc.) is required, and it cannot be used outside of network coverage.

• CLAS (satellite-communication-based augmentation): This is a method that uses the centimeter-level augmentation service (CLAS) provided by Japan's Quasi-Zenith Satellite System "Michibiki". Technically called PPP-RTK, it computes error information from data of the government-maintained network of electronic reference stations (GEONET), and the Michibiki satellites broadcast that information across Japan via the L6 radio signal. Users directly receive correction signals from the satellite with a CLAS-compatible receiver and apply the corrections to their positioning. Because no communication line is required, it can be used in mountainous areas and during communication outages, and there are no distance restrictions from base stations. Another advantage is that signal reception itself is provided free of charge. However, note that a dedicated receiver is required; horizontal accuracy may be slightly inferior—CLAS is about 6 cm compared with RTK's about 2 cm—initial high-precision positioning can take tens of seconds to about one minute, and the service area is limited to within Japan.

Differences and Comparison Points Among Methods (Accuracy, Cost, Environmental Constraints, Implementation Difficulty)

Let's compare the differences between the above-listed conventional RTK, network RTK, and CLAS from several perspectives.

• Accuracy: All methods, when operated properly, can achieve horizontal accuracy on the order of several centimeters. Conventional RTK and network RTK (VRS) are effectively equivalent, consistently producing errors within a few centimeters. The CLAS method can also achieve centimeter-level accuracy when stable, but strictly speaking its errors can be slightly larger than RTK's (around 5–6 cm horizontally) in some cases. Additionally, CLAS differs in that it takes time for accuracy to converge immediately after positioning begins, remaining in a float solution stage with errors of several tens of centimeters for the first few dozen seconds.

• Initial cost: Traditional RTK requires high-performance GNSS equipment for both the base station and the rover (mobile station), making equipment costs high. Network RTK does not require a private base station, and since you only need to prepare a receiver for the rover, the initial investment is lower. The CLAS method also does not require a base station, but purchasing a CLAS-compatible receiver (a domestic high-precision GNSS device) is necessary. In general, the traditional type that requires dedicated equipment is the most costly, while network-based and CLAS-compatible devices are relatively less expensive. Recently, whereas traditional equipment costs several million yen, small smartphone-compatible devices have become available from around a few hundred thousand yen.

• Operational costs: In conventional RTK, because correction information is basically sent from one's own system, there are almost no running costs (however, communication and maintenance costs for the base station are incurred). Network RTK incurs periodic subscription fees (annual or monthly) for correction data distribution services. CLAS is a signal provided free of charge by the government, so no usage fees are required. Therefore, running costs should only be a concern for the network type, but in many cases these are more than offset by reduced base station management effort and labor costs.

• Environmental constraints: Conventional RTK requires radio communication between the base station and rover within range (a few kilometers is ideal), and an environment where the sky is open at both locations so GNSS signals can be received. Network RTK can be used anywhere in Japan as long as you are within communication coverage such as a mobile network, and you do not need to be concerned about the distance to the reference points for corrections. However, it cannot be used inside tunnels or outside base station coverage. CLAS can be used anywhere without communication as long as it is an outdoor environment where signals from satellites reach. Its strength is that it can provide positioning even in mountainous areas or immediately after disasters where communication infrastructure is absent; conversely, in forests where artificial satellites are hard to see or in urban canyons between high-rise buildings, signal reception can become unstable and maintaining accuracy may be difficult.

• 導入難易度: Conventional RTK requires tasks such as setting up base stations and configuring equipment, so expert knowledge is required, making operational hurdles relatively high. Network RTK is comparatively simple and easy to handle because once you set the receiver and establish a communication connection, corrections are received automatically (a service contract and software configuration are necessary, but once configured there is no need to set up a base station for each site). With CLAS, as long as you have compatible equipment ready, you simply power it on outdoors and it will automatically receive correction signals and start positioning. It is simple in that no communication configuration is required, but note that preparing compatible models and the initial convergence can take some time. Overall, conventional RTK has the highest difficulty, while network RTK and the CLAS method stand out for their ease in field operations.

Background and Advantages of Smartphone RTK Surveying

Traditionally, surveying relied on optical instruments such as total stations and levels, and was usually carried out by two-person teams. An experienced surveyor had to operate the equipment while an assistant held the staff at the survey points, which required both manpower and time. Furthermore, even when attempting more advanced GNSS surveying, fixed, expensive equipment had to be procured, making it impractical to perform with a small crew.

However, in recent years the construction industry has been facing a severe labor shortage and the aging of skilled workers, increasing the need to run sites efficiently with fewer personnel. One solution that has attracted attention is surveying that can be completed by a single person. The government is also promoting the adoption of ICT technologies to reduce manpower and improve productivity at construction sites; for example, the Ministry of Land, Infrastructure, Transport and Tourism's *i-Construction* advocates efficiency through the use of 3D data and automated construction. Against this backdrop, a technology has emerged that makes "surveying that anyone—even a single person—can perform" possible by combining a smartphone and RTK-GNSS. That is smartphone RTK surveying.

Translation target: There are various advantages to smartphone RTK surveying that traditional methods do not have. Let's list the main benefits.

• Labor savings and reduced manpower: With just a smartphone and a compact GNSS receiver, a single person can complete surveying work. Even on large sites, the person in charge can perform position measurements simply by walking with a smartphone in hand, eliminating tasks such as two-person teams carrying heavy equipment. There is no need to organize surveying crews, making it easier to cope with sites facing personnel shortages.

• Reduced work time: RTK enables high-precision coordinates to be obtained on site instantly, making real-time positioning possible. If you hold your smartphone at the point you want to measure and press a button, data acquisition is completed immediately, greatly reducing the time spent setting up equipment and taking readings at each measurement point as in conventional methods. Because you can check the results immediately, you can also reduce rework, such as having to return later after discovering errors.

• High-precision positioning: Standalone smartphone GPS has an error of about 5–10 m, but smartphone RTK can achieve accuracy of several centimeters. Even for tasks that require high precision, such as terrain surveying or verifying the installation of structures, sufficiently reliable results can be obtained on-site.

• Cost reduction: Instead of purchasing expensive optical surveying instruments or dedicated GNSS equipment, you can use existing smartphones and relatively inexpensive GNSS receivers, significantly reducing initial deployment costs. Equipment maintenance and management expenses are also lowered, making it more accessible to small- and medium-sized businesses.

• Ease of data use: Survey data captured on a smartphone is saved in digital format from the start. There's no need to handwrite in a paper field notebook and later transcribe it to a PC; you can upload it directly to the cloud or import it into CAD or GIS software. This reduces human error and omissions, making data organization and sharing smoother.

• Multifunctional use: By combining a smartphone’s camera and sensors, a range of measurements beyond simply measuring point coordinates becomes possible. For example, you can record survey points with photos, overlay plans onto live site imagery using AR (augmented reality) for positioning, or obtain 3D point clouds with the built-in LiDAR scanner, realizing an integrated solution unique to smartphones. These features are introduced in detail in the LRTK system described below.

Thus, smartphone RTK surveying is not only high-precision and low-cost, but can also be described as a surveying method suited to the DX era, with immediate data sharing and AR utilization. It enables anyone on site to routinely perform surveying tasks that were traditionally left to specialists, and is significantly changing the way people work on construction and surveying sites.

Main features of the LRTK system (AR guidance · point cloud scanning · cloud sharing · photogrammetry · etc.)

A concrete product example supporting smartphone RTK surveying is the LRTK series, developed by Reflexia, a startup originating from the Tokyo Institute of Technology. The LRTK consists of an ultra-compact RTK-GNSS receiver that can be attached to an iPhone, a dedicated app, and cloud services, forming a pocket-sized system that enables high-precision field surveying. Using this LRTK, various measurement tasks that previously required multiple devices and advanced skills can be performed with just one smartphone. Let's take a look at the main features of the LRTK system.

• AR-guided positioning and surveying: Display design data and reference lines as AR overlays on a smartphone screen to perform on-site positioning and as-built checks. For example, when you approach a pre-entered stake location, arrows and guide lines appear on the screen, and simply driving the stake at the indicated spot completes accurate layout work. Machine operators can also work while viewing a virtual excavation line through a smartphone screen from the operator's seat. This allows even novices to work accurately with visual guidance instead of relying on a skilled worker's intuition, leading to labor savings by eliminating batter boards and reducing construction errors.

• Point cloud scanning (3D measurement): Using the LiDAR scanner built into smartphones (supported models only) and cameras, you can acquire three-dimensional point cloud data of a site. With LRTK, you can scan surrounding terrain and structures simply by walking while holding your smartphone, and a high-precision 3D point cloud model is generated on-site. Since the acquired point cloud is assigned world-coordinate position information from the start, alignment when merging multiple scan datasets is also automatic. The generated point cloud can be instantly overlaid and compared with the design model, and analyses such as color-coding differences from the design for construction/as-built inspections are possible with a single tap. Tasks that previously required specialized 3D laser scanners can now be carried out easily with a smartphone and LRTK (※The smartphone LiDAR feature is available on recent iPhone and iPad Pro models).

• Cloud sharing and real-time collaboration: Survey data and photos captured with LRTK can be automatically synced to the cloud on-site. Point cloud data and coordinate values measured in the field are immediately uploaded to the cloud, allowing results to be viewed and shared in real time from office PCs. By eliminating information transmission lag between the field and the office, remote supervisors or clients can grasp site conditions and give instructions from afar. This shortens the traditional workflow of returning to the office after surveying to prepare reports, supporting speedy consensus building and decision-making.

• Photogrammetry and High-Precision Photo Recording: You can also perform photogrammetry using a smartphone camera and RTK. The LRTK series includes drone-mounted models, and when mounted on a drone, high-precision position tags are attached to all aerial photos, greatly improving the accuracy of orthophotos and 3D terrain models. On the ground, multiple photos taken with a smartphone can be processed with dedicated software to create high-precision 3D reconstruction models. Because they include location information, the model’s scale and orientation can be accurately reproduced. The LRTK app also includes a photo-capture feature that can automatically tag the exact coordinates at the moment to on-site photos taken. During routine inspections of bridges and roads, cracks found can be recorded as photos with latitude and longitude rather than as “X meters from column No. Y,” which is useful for later comparison and repair planning. Unlike paper ledgers, digital photo records are easy to search and share, improving the quality of infrastructure inspection operations.

Additionally, LRTK also offers a starter kit that includes a detachable monopod and a smartphone holder, with design features that enable even beginners to take straight, stable measurements. LRTK, which can handle everything from full on-site 3D measurement to data sharing with just a receiver weighing approximately 125 g and a smartphone, is attracting attention as a next-generation all-purpose surveying tool.

Operational Transformations Enabled by Smartphone RTK (Labor Reduction, Time Savings, Remote Support, As-Built Management, etc.)

The introduction of smartphone RTK will significantly change on-site workflows and the way people work. Here, let's outline those transformations using keywords such as labor reduction, time savings, remote support, and as-built management.

• Labor reduction (fewer personnel): With smartphone RTK enabling surveying with one device per person, waste such as "other work coming to a halt while waiting for surveying" is eliminated. Because surveying that previously required two people can be handled by one, it becomes easier to keep operations running even on sites facing labor shortages. If multiple work crews can each perform their own surveying, they can proceed without waiting for a dedicated surveying team, leading to improved productivity across the entire site.

• Reduced work time: Traditionally, survey results were taken back to the office for drafting and review, but with smartphone RTK, real-time surveying and instant sharing become standard practice. Because measured data can be shared on-site via the cloud, remote supervisors and designers can immediately check it and issue the next instructions. Even if rework or additional measurements are required, they can be handled immediately on site. As a result, the overall lead time for the process is shortened, and secondary benefits such as reduced idle time for heavy machinery and shorter construction periods can be expected.

• Remote support and information sharing: By storing and sharing data obtained with smartphone RTK in the cloud, a system can be established in which the field and the office are connected at all times. For example, while a field staff member conducts surveying, an engineer in the office can view the results in real time and provide advice, or the client can check the as-built data online. Because checks and consensus can be made on the spot without waiting for in-person inspections or sequential reports, communication loss is reduced and speedy decision-making becomes possible. This accelerates the PDCA cycle of construction management, achieving both quality assurance and efficiency.

• Advanced As-built Management and Inspection: Because point cloud data and survey data acquired in 3D are accumulated daily in the cloud, as-built management and the preparation of various inspection documents are dramatically streamlined. For example, for as-built inspections at project completion, reports and forms can be generated with one click from data on the LRTK cloud. Automatic reports of survey results with photos can also be easily output, greatly reducing the time required to prepare inspection documents. During joint inspections with the client, you can explain while viewing the point cloud model together on a tablet, enabling smooth agreement. Inspection and maintenance tasks that were previously burdened by handwritten paper ledgers and photo organization achieve greater efficiency and improved accuracy through digital management.

By utilizing smartphone RTK in this way, on-site productivity and quality will dramatically improve. Combined with effects such as reduced human error from high-precision positioning and improved safety (reducing the number of surveys at heights and in hazardous areas), a new on-site operation that places less burden on workers is becoming a reality. As surveying conventions change and an environment where "anyone can take measurements immediately whenever needed" is established, construction management will become faster and more reliable than ever before.

Case Studies of On-Site Implementations and Effects (Efficiency Differences Compared to Conventional Methods)

Sites that have actually implemented smartphone RTK or LRTK have reported substantial efficiency improvements compared with conventional methods. Here we introduce several implementation cases and examine their effects.

• Integrated surveying at a road construction site: On a new road construction project, a single smartphone equipped with LRTK was used to perform everything from control-point surveying to 3D scanning of as-built areas and AR verification against the design model. Whereas the conventional process—establishing control points with a total station, capturing point clouds with a 3D laser scanner, and comparing against design data on an office PC—used to take several days, after introducing LRTK it was completed in just one day. Because the site personnel were able to measure and verify on the spot without waiting for a specialist surveying team, this is an excellent example of major labor savings and speed-up across the entire workflow. It overturned the conventional wisdom of "waiting several days to confirm as-built accuracy within a few centimeters," and site staff praised it, saying "we no longer wait on surveys, which has made schedule management easier."

• Use of AR in Heavy Equipment Operation: On another site, we applied LRTK's AR functionality to excavation work performed by heavy machinery. The planned excavation design lines were preloaded into the LRTK app, and during construction virtual guidelines were displayed in AR on the smartphone screen. Operators only needed to move the shovel along the lines shown on the screen to excavate to the design's intended shape and slope. Because this method allowed accurate work even without installing batter boards (layout markings), it contributed to shorter work times and reduced manpower. Since operators can simply follow the lines on the screen even if they are not veterans, variations in accuracy due to differences in skill were eliminated. As a result, rework was reduced and safety improved, and site supervisors have 평가ed it as "reliable enough to entrust to novice operators."

• Immediate measurement and sharing with one device per person: The cost advantages should not be overlooked. Traditionally, equipping a site with a complete RTK surveying setup required an investment of several million yen. However, a pocket-size LRTK can be introduced at an order of magnitude lower price, making it realistic to equip each operator with one device even on sites that previously shared a single expensive unit. At one civil engineering firm, site managers and foremen now carry LRTKs and have started an operation in which each person routinely performs surveying and checks. By taking measurements themselves at the necessary moment and sharing the results with stakeholders via the cloud, they help prevent construction errors and optimize construction processes. Data sharing also tightens coordination between the site and headquarters, enabling early detection and correction of issues. The agile PDCA cycle created by “being able to measure whenever you want” and “measured data being immediately shared” is precisely a new on-site workflow unique to the smartphone RTK era.

As described above, the effects of introducing smartphone RTK extend to many areas, including work efficiency, accuracy, cost, and safety. Of course, in some cases—such as control-point surveying that requires millimeter-level accuracy—there still remains a role for traditional precision instruments and experienced technicians, but in many field operations smartphone RTK delivers practically sufficient accuracy and overwhelming efficiency. Even in comparisons with conventional methods, its advantages are clear, and it is becoming widely adopted as a powerful tool to accelerate on-site DX.

Advice for Prospective Adopters (Selection Points, Cautions, Initial Implementation Procedures)

For those planning to adopt smartphone RTK surveying, we offer advice on key points for equipment selection, operational cautions, and initial implementation procedures to help you get started smoothly.

• Device and service selection: First, check the compatibility between the smartphone you will use and the GNSS receiver device. For example, the LRTK series currently supports iPhone and operates via an iOS app with a Bluetooth connection (Android support is expected in the future). The smartphone itself does not need to be the latest model, but if you want to leverage built-in sensors (LiDAR, etc.), a high-performance device such as an iPhone Pro model is desirable. For the GNSS receiver, consider whether to choose a CLAS-compatible model based on your coverage area and needs. If there is a possibility you will use it in mountainous areas outside cellular coverage, a model that can receive the Michibiki CLAS signal provides peace of mind. Conversely, if you will mainly operate in urban areas, a network-RTK-only model is acceptable. In addition, be sure to consider subscribing to correction information services (such as VRS). Since municipal and private distribution services exist regionally, choose a plan suitable for your organization’s area of use.

• Operational environment and precautions: Before deployment, confirm that smartphone RTK will function adequately in your actual site environment. GNSS relies on a clear view of the sky, so if the location you want to position has an extremely restricted sky view (urban canyons or under tree canopy) accuracy may be poor. In that case, consider choosing the time of day (aim for favorable satellite geometry) or taking supplementary measures such as using a total station in combination. Also, because smartphone RTK is electronic equipment, battery management is important. Make sure both the smartphone and the GNSS device are fully charged, and for long continuous surveys bring a mobile battery pack. Take waterproofing measures for rainy conditions (LRTK terminals are dust- and water-resistant, but put a cover on the smartphone, etc.), and be mindful of overheating in the midsummer sun (cool devices in the shade as needed, etc.).

• Practice and internal rollout before deployment: Before using it directly on a live site, first carry out a trial operation within the company or in a safe location. Following the operation manual, check the app’s basic operations, the positioning workflow, and methods for saving and sharing data. Test outdoors where GPS reception is good and verify whether the expected accuracy is achieved and whether the data format is compatible with your drawing/CAD software. Share usage procedures not only with site supervisors and surveying staff but also with the workers who will actually use it, and conduct a brief training session for reassurance. Fortunately, smartphone RTK is handled like an app, so there are almost no complicated operations, but understanding the positioning principles and precautions will help you stay calm and respond appropriately in case of problems.

• Initial deployment procedure: Once the decision to deploy has been made, proceed with preparations according to the following steps. 1. Equipment preparation: Purchase or rent the GNSS receiver unit and obtain holders or poles that can attach to your smartphone. It's a good idea to start with recommended accessories such as a starter kit. 2. App installation and configuration: Install the dedicated app on your smartphone and complete user registration and login. Next, pair the receiver with the app via Bluetooth and confirm the connection. Also configure the account information for the correction service (VRS) you will use. 3. Outdoor operation check: Go outdoors where the sky is open, turn on the equipment, and confirm in the app that satellites are being acquired. Begin receiving correction data; after about 30 seconds the status should become "Fix". After obtaining a Fix solution, measure a known point to verify accuracy. If centimeter-level accuracy is achieved without problems, you are ready. 4. Field deployment: Finally, start smartphone RTK surveying at actual sites. At first, try it on lower-priority tasks (such as preliminary site reconnaissance surveys), and gradually expand its use to main tasks like stakeout and as-built management. Provide feedback on the benefits and issues obtained at each site and accumulate know-how within the company.

By following the steps above, you should be able to start operating smartphone RTK without any particular hiccups. If you run into problems, make use of the manufacturer's support and FAQs, and prioritize safety as you establish this new technology on site.

Guide to Implementing LRTK for Simple Surveying

Have you gained a deeper understanding of the appeal of smartphone RTK surveying and the key points for implementation? Finally, for those looking to begin high-precision simple surveying, we will provide an implementation guide with the use of LRTK in mind.

LRTK was developed with the concept of "a pocket-sized surveying instrument anyone can use," and is a system that combines the conventional-defying ease of use and high precision. Attach the dedicated unit to your smartphone and turn it on; it automatically acquires correction information and can begin centimeter-accurate positioning in about 20–30 seconds. Then, simply follow the on-screen instructions and press a button, and accurate latitude, longitude, and height are recorded instantly. There is no need to set up a tripod or spend a long time on preparatory work, and its major appeal is that you can measure immediately whenever you think of it.

Moreover, LRTK is compact and lightweight and easy to carry, and it is waterproof, dustproof, and shock-resistant, so it can be used with confidence even in harsh field environments. Measured data are stored in the cloud and can be shared with stakeholders in real time, allowing it to function as a trump card for on-site DX (digital transformation). Pricing is also lower than that of existing high-precision GNSS devices, making it easy to adopt as a first high-precision positioning tool.

Even those using surveying equipment for the first time can handle LRTK without resistance if they are familiar with operating a smartphone. The era of completing on-site surveys "quickly with a smartphone" is just around the corner. Please take this opportunity to consider smartphone surveying with LRTK. The once cumbersome surveying tasks will become surprisingly accessible, allowing you to improve on-site productivity while enhancing quality.

FAQ

Q1. Can't the built-in GPS in smartphones achieve RTK-level high precision? A1. Unfortunately, at present it is not possible to obtain centimeter-level accuracy using only a smartphone's built-in GPS. A smartphone's standard GPS has errors on the order of several meters and does not provide access to the raw carrier-phase data required for RTK. Therefore, to achieve centimeter-level high-precision positioning you need to use an RTK-capable external GNSS receiver (for example, an LRTK terminal). This external device performs high-precision positioning computations applying correction information, and by delivering those results to the smartphone, RTK positioning becomes possible on the smartphone as well.

Q2. Is the accuracy of smartphone RTK really reliable? Is it comparable to a total station? A2. Yes—when operated correctly, smartphone RTK can provide accuracy that is practically sufficient. For example, experiments with LRTK devices have shown that positioning errors at the same point differ by only a few millimeters compared to high-performance GNSS receivers equivalent to the Geospatial Information Authority of Japan’s first-class standard. Compared to the typical accuracy of total station surveys (several mm to about 1 cm) or conventional RTK-GNSS (several cm), smartphone RTK’s errors within a few centimeters are not inferior. It can meet the accuracy required for construction sites and surveying tasks, so you can use it with confidence without worrying that its smaller size means lower accuracy.

Q3. 携帯の電波が届かない山奥や災害時でもスマホRTKは使えますか？ A3. Even in environments where communications infrastructure is unavailable, smartphone RTK can be operated if conditions permit. The key to this is Michibiki (QZSS)'s CLAS signal. If you prepare a CLAS-compatible receiver in advance (e.g., the LRTK Pro series), you can receive correction data directly from the quasi-zenith satellite even outside mobile network coverage and continue centimeter-level positioning. In fact, there have been cases where damage assessments were carried out using CLAS-capable compact GNSS devices at disaster sites where cellular networks were down. However, in environments with no line of sight at all (deep forests or inside tunnels), satellite signals themselves are difficult to receive, so in such cases you will need to re-survey later or supplement with other methods.

Q4. Can accurate positioning be achieved in urban areas with tall buildings or in forests? A4. In areas lined with high-rise buildings or in places with dense tree cover, signals from GNSS satellites can be blocked by buildings or foliage, which may cause positioning to take longer or reduce accuracy. Even when using RTK corrections, if the satellite signals themselves cannot be received sufficiently, maintaining centimeter-level accuracy is difficult. For this reason, in urban areas you should measure at intersections with as much open sky as possible or where the gaps between buildings are wide, and in forests measure where the trees thin out or at times when the satellite geometry overhead is favorable. If that still proves difficult, consider using different methods as appropriate, such as temporarily measuring that single point with a total station. Conversely, smartphone RTK performs very well in locations with good visibility, so it is recommended to flexibly apply it according to the site conditions.

Q5. Do you need any special contracts or licenses to receive correction information? A5. To use smartphone RTK with high accuracy, you basically need to use some kind of correction information service. For network RTK, you subscribe to a commercial VRS distribution service or an RTK service provided by a mobile carrier and set that account information in the app (in some areas, free correction services run by local governments are available). On the other hand, when using the CLAS method, no contract is required, but a compatible receiver limited to use within Japan is necessary. Note that a radio station license is usually not required. Traditionally, a license for a UHF radio at the base station was required, but correction obtained via the internet or satellite does not use additional radios (smartphone communications and satellite reception are permitted for general use). As for surveying qualifications, no license is required to operate the equipment itself (however, to use results as official public survey data, the work must be carried out under the supervision of a licensed surveyor). In summary, as long as you have the equipment and a communication environment, anyone can start using smartphone RTK without special licenses.

Q6. Will it work with any smartphone model? Does it work on Android devices? A6. At present, many smartphone RTK solutions are designed to operate on iPhone/iPad (iOS). For example, with LRTK you attach it to an iPhone and use an app. Support for Android devices must be confirmed separately, but support may expand in the future. Meanwhile, any iPhone model that supports the latest OS can generally be used. However, some features (such as point cloud scanning and camera-based subject positioning) require a Pro model equipped with a LiDAR scanner. If possible, using a high-performance device like the latest iPhone 15 Pro will further improve positioning accuracy and AR display stability. Select the compatible receiver and app according to the smartphone you have.