Table of Contents

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

• Differences between each method and comparison points (accuracy, cost, environmental constraints, implementation difficulty)

• Background and advantages of smartphone RTK surveying

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

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

• On-site implementation case studies and effects (efficiency differences compared to traditional methods)

• Advice for those considering implementation (selection points, cautionary notes, initial implementation steps)

• Guidance on introducing LRTK for simplified surveying

• FAQ

Smartphone-based RTK surveying, which combines smartphones and GNSS technology, is attracting significant attention at construction and civil engineering sites. RTK-GNSS-based centimeter-level (half-inch accuracy) high-precision positioning has become easily accessible to anyone, enabling intuitive work support through AR displays and even point-cloud scanning using LiDAR. Amid worsening labor shortages, "surveying that one person can do" and "measurements that can be shared in real time" are solutions that directly improve on-site productivity. This article explains in detail the basics of RTK-GNSS and the differences between its methods, the advantages brought by smartphone RTK and concrete use cases, and even 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 (USA), GLONASS (Russia), Galileo (Europe), and Michibiki (Japan's Quasi-Zenith Satellite System). A GNSS receiver receives radio signals from multiple satellites and calculates the current position (latitude, longitude, altitude) from the distance to each satellite. However, with standalone positioning, errors in signal propagation and other factors limit position accuracy to several meters (several ft). Typical smartphone built-in GPS also has errors of about 5-10 m (16.4-32.8 ft), which makes it unsuitable for precise surveying.

This error correction method that achieves centimeter-level positioning accuracy (half-inch accuracy) is RTK (Real-Time Kinematic) positioning. In RTK, both a base station (a receiver installed at a known accurate position) and a rover (a portable receiver) receive GNSS signals simultaneously. The base station calculates the discrepancy between its known accurate 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 correction to its positioning data, which can improve positions that were off by several meters (several ft) to within a few centimeters (within a few in). This is possible because it uses the carrier phase of the satellite signal, a precise ranging signal that can detect distance differences down to the millimeter level. The advent of RTK has made real-time high-precision positioning practical in a wide range of fields such as civil surveying, agriculture, and autonomous driving.

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

• Conventional RTK (standalone): This method has the user install a dedicated base station near the site and transmit correction information to the rover by radio. It provides high accuracy with a simple one-to-one configuration, but requires the effort of setting up the base station each time, and accuracy decreases the farther you are from the base station. In general, when more than 10 km (6.2 mi) away from the base station, error correction becomes difficult. It also required purchasing dedicated equipment and specialized operational knowledge, so the barrier to adoption was relatively high.

• Network RTK: It is a method that 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 through communication infrastructure such as mobile networks, there is no need to set up your own base station, and you can start positioning anywhere immediately. Even when moving over a wide area, corrections from a nearby virtual reference station are always available, reducing accuracy degradation due to distance. However, a subscription to the correction service (monthly fees, etc.) is required, and there is the limitation that it cannot be used outside communication coverage.

• CLAS (satellite-communication augmentation): This is a method that uses the centimeter-level augmentation service (CLAS) provided by Japan’s Quasi-Zenith Satellite System “Michibiki”. Technically known as PPP-RTK, it computes error information from data of the nationally maintained network of continuously operating reference stations (GEONET), and the Michibiki satellites broadcast that information across Japan via the L6 signal. Users directly receive the correction signals from the satellites with a CLAS-compatible receiver and apply the corrections to their own positioning. Because no communications line is required, it can be used in mountainous areas and during communications outages, and there is no distance restriction from a base station. Another advantage is that receiving the signal itself is provided free of charge. However, note that a dedicated receiver is required; horizontal accuracy may be somewhat less accurate, with RTK at about 2 cm (0.8 in) versus CLAS at about 6 cm (2.4 in); initial high-precision positioning can take several tens of seconds to about one minute; and the service coverage is limited to within Japan.

Differences between each method and comparison points (accuracy · cost · environmental constraints · implementation difficulty)

Let's compare the differences among the above-mentioned Conventional RTK, Network RTK, and CLAS from several perspectives.

• Accuracy: If any of the methods are operated properly, horizontal accuracy of a few centimeters (a few in) can be obtained. Conventional RTK and network RTK (VRS) are effectively equivalent, with errors always within a few cm (a few in). The CLAS method can also achieve several centimeter accuracy (cm level accuracy, half-inch accuracy) when stable, but strictly speaking there are cases where its errors are slightly larger than RTK (horizontal about 5–6 cm (2.0–2.4 in)). Also, CLAS differs in that immediately after positioning begins it takes time for accuracy to converge; during the first several tens of seconds the error remains at the float-solution stage on the order of several tens of centimeters (several tens of in).

• Initial cost: Conventional RTK requires high-performance GNSS equipment for both the base station and the rover, so equipment costs are high. Network RTK does not require owning a base station, and since you only need to prepare only the receiver for the rover, the initial investment can be kept low. The CLAS method also does not require a base station, but you need to purchase a CLAS-compatible receiver (high-precision GNSS device for the domestic market). Overall, the conventional type that requires dedicated equipment is the most costly, while network-based and CLAS-compatible devices are relatively less expensive. Recently, whereas conventional equipment costs several million yen, small smartphone devices are now available from around several hundred thousand yen.

• Operational costs: With conventional RTK, because correction information is basically transmitted in-house, there are almost no running costs (however, communication and maintenance costs for base stations are incurred). Network RTK incurs periodic subscription fees (annual or monthly) for correction data distribution services. CLAS is a government-provided signal offered for free, so no usage fee is required. Therefore, only the network type requires attention regarding running costs, but in many cases these costs can be more than offset by reduced base station management effort and labor cost savings.

• Environmental constraints: Conventional RTK requires an environment where radio communication can reach between the base station and the rover (a few km is ideal), and 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 the coverage area of cellular networks such as mobile phones, and you do not need to be concerned about the distance to the correction reference points. However, it cannot be used inside tunnels or outside the base station’s coverage. CLAS can be used anywhere without communications as long as it is an outdoor environment where signals from satellites can reach. Its strength is that it can provide positioning even in mountainous areas or immediately after disasters when communication infrastructure is unavailable, but conversely it can be difficult to maintain accuracy because signal reception becomes unstable in forests where satellites are hard to see or in urban canyons between tall buildings.

• Implementation difficulty: Traditional RTK requires specialized knowledge such as base station setup and equipment configuration procedures, so its operational hurdle is relatively high. Network RTK is comparatively simple and easy to handle because once the receiver is set and connected, corrections are received automatically (a service contract and software configuration are required, but once configured, base station deployment at each site is unnecessary). With CLAS, as long as compatible equipment is prepared, you simply power it on outdoors and it will automatically receive correction signals and begin positioning. It is simple in that communication configuration is also unnecessary, but note that preparing compatible devices and the initial convergence may take some time. Overall, traditional RTK has the highest difficulty, while network RTK and CLAS stand out for their ease of use in field operations.

Background and Advantages of Smartphone RTK Surveying

Traditional surveying used optical instruments such as total stations and levels, and was generally carried out by teams of two. An experienced surveyor would operate the equipment, and an assistant would hold the staff at the survey point, requiring manpower and time. Moreover, even if one wanted to perform advanced GNSS surveying, one had to prepare fixed, expensive equipment, so it could not be done easily with a small crew.

However, in recent years the construction industry has been facing a serious labor shortage and an 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 introduction of ICT technologies to reduce personnel 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 three-dimensional data and automated construction. Against this backdrop, a technology that enables "surveying that anyone — even a single person — can perform" has emerged by combining a smartphone with RTK-GNSS. That is smartphone RTK surveying.

Smartphone RTK surveying offers various advantages that traditional methods do not. Let's list the main benefits.

• Labor savings and reduced staffing: With only a smartphone and a compact GNSS receiver, one person can complete surveying tasks. Even on large sites, the person in charge can measure positions simply by walking with a smartphone in hand, eliminating tasks such as two people carrying heavy equipment. There is no need to organize a surveying crew, making it easier to handle understaffed sites.

• Reduced working time: Because RTK provides high-precision coordinates on site instantly, real-time positioning is possible. If you hold your smartphone over the point you want to measure and press the button, the data is acquired immediately, so the time spent setting up equipment and taking readings at each survey point as was done before is greatly reduced. Since you can check the results right away, you can also reduce rework such as having to return later after discovering an error.

• High-precision positioning: Standalone smartphone GPS has errors of approximately 5–10 m (16.4-32.8 ft), but smartphone RTK achieves centimeter-level accuracy (half-inch accuracy). Even for tasks that require high precision, such as topographic surveying and verification of installed structures, sufficiently reliable results can be obtained on site.

• Cost reduction: Instead of purchasing expensive optical surveying instruments and dedicated GNSS equipment, you can use your existing smartphone and relatively inexpensive GNSS receiver devices, significantly reducing initial implementation costs. Equipment maintenance costs are also lowered, making it more accessible to small and medium-sized businesses.

• Ease of data utilization: Survey data collected using a smartphone are saved in digital format from the start. There is no need to handwrite in a paper field notebook and later transcribe it to a PC…, so you can upload the data directly to the cloud or import it into CAD or GIS software. This reduces human error and missed entries, making data organization and sharing smoother.

• Versatile functionality: By combining a smartphone’s camera and sensors, you can perform a wide range of measurements that go beyond simply measuring point coordinates. For example, you can record survey points with photos, overlay design drawings onto live site imagery using AR (augmented reality) for positioning, and acquire 3D point clouds with a built-in LiDAR scanner, realizing an all-in-one smartphone solution. These features will be detailed in the LRTK system described later.

In this way, smartphone RTK surveying is not only high-precision and low-cost, but can also be said to be a surveying method suited to the DX era, enabling immediate data sharing and AR use. What had traditionally been entrusted to specialists can now be performed daily by anyone on site, fundamentally 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.)

As a concrete product example supporting smartphone RTK surveying, there 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, making it a pocket-sized system that enables high-precision on-site surveying. By using this LRTK, various measurement tasks that previously required multiple devices and advanced skills become possible with just one smartphone. Let's look at the main features of the LRTK system.

• AR-based guidance and surveying: You can display design data and reference lines on a smartphone screen as AR, enabling on-site positioning and as-built checks. For example, when you approach a pre-entered stake position, arrows and guide lines appear on the screen, and by simply driving the stake at the indicated spot the precise batter board layout work is completed. Heavy equipment operators can also work while viewing a virtual excavation line through the smartphone screen from the operator's seat. This allows even newcomers to perform tasks accurately using visual guidance instead of relying on the intuition of experienced workers, leading to labor savings by omitting batter boards and preventing construction errors.

• Point cloud scanning (3D measurement): Using the smartphone’s LiDAR scanner (on supported models) or camera, you can acquire 3D point cloud data of a site. With LRTK, simply walking while holding your smartphone lets you scan surrounding terrain and structures, and a high-precision 3D point cloud model is generated on the spot. Because the acquired point clouds are assigned position information in world coordinates from the start, alignment when merging multiple scan datasets is automatic. The generated point clouds can be immediately overlaid and compared with the design model, and for as-built inspections, analyses such as color-coded displays of deviations from the design can be performed with a single tap. Tasks that previously required specialized 3D laser scanners can now be easily performed with a smartphone and LRTK (※The smartphone LiDAR feature is available on recent iPhone and iPad Pro models).

• Cloud sharing and real-time coordination: Survey data and photos acquired with LRTK can be automatically synchronized 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 checked and shared in real time from office PCs. Eliminating information transmission lag between the field and the office makes it possible for remote supervisors or clients to understand site conditions remotely while issuing instructions. This shortens the traditional procedure of returning to the office after surveying to prepare reports, and supports speedy consensus building and decision-making.

• Photogrammetry / High-accuracy Photo Records: You can also perform photogrammetry (photogrammetry) using a smartphone camera and RTK. The LRTK series includes drone-mount models, and when mounted on a drone high-precision position tags are added to all aerial photos, dramatically improving the accuracy of orthophotos and 3D terrain models. On the ground as well, processing multiple photos taken with a smartphone using dedicated software can produce high-accuracy 3D reconstruction models. Because they include position information, the model’s scale and orientation can be reproduced accurately. The LRTK app also has a photo capture function that can automatically tag captured site photos with the exact coordinates at that moment. During routine inspections of bridges and roads, the locations of cracks found can be recorded as photos with latitude and longitude instead of as “from pier No. X, X m”, which is useful for later comparisons and repair planning. Unlike paper ledgers, digital photo records are easy to search and share, improving the quality of infrastructure inspection operations.

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

Operational transformations made possible by smartphone RTK (labor reduction, time savings, remote support, as-built management, etc.)

The introduction of smartphone RTK significantly changes on-site workflows and work styles. Here, let’s organize those transformations around keywords such as labor reduction, time savings, remote support, and as-built management.

• Labor reduction (fewer personnel): With smartphone RTK enabling one device per person for surveying, wasted delays such as other work stopping while waiting for surveying are eliminated. Because surveying that previously required two people can now be handled by one, operations become easier to maintain even at sites with labor shortages. If multiple work crews can each carry out their own surveying, they can proceed without waiting for a specialized surveying team, leading to improved productivity across the 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 the norm. Because measured data can be shared on the spot via the cloud, remote supervisors or designers can immediately check it and issue the next instructions. Even if rework or additional measurements are required, they can be addressed on-site right away. As a result, the lead time for the entire process is shortened, and secondary benefits such as reduced heavy-equipment idling time and shorter construction schedules can be expected.

• Remote support and information sharing: By storing and sharing data obtained with smartphone RTK in the cloud, you can build a system in which the field and the office are constantly connected. For example, a site staff member can take measurements while office engineers view the results in real time and provide advice, or clients can check as-built data online. Without waiting for in-person inspections or sequential reports, checks and consensus can be reached on the spot, reducing communication loss and enabling speedy decision-making. This accelerates the PDCA cycle of construction management, allowing both quality assurance and improved efficiency.

• Advancing 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 creation of various inspection documents are dramatically streamlined. For example, during as-built inspections at completion, reports and forms can be generated from data on the LRTK cloud with a single button. Automatic reports of survey results with photos can also be easily output, significantly reducing the time required to prepare inspection documents. Also, 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 tied up with handwritten paper ledgers and organizing photos are achieving improved efficiency and accuracy through digital management.

As such, by leveraging smartphone RTK, on-site productivity and quality will improve dramatically. Combined with effects such as reduced human error from high-precision positioning and enhanced safety (fewer surveys at elevated or hazardous locations), a new on-site operational model that places less burden on workers is beginning to take shape. Surveying conventions are changing, and by creating an environment where "anyone can measure immediately when needed," construction management will become faster and more reliable than ever before.

Field deployment case studies and effects (efficiency differences compared with conventional methods)

Actual sites that have implemented smartphone RTK and LRTK have reported significant efficiency improvements compared with conventional methods. Here we introduce several implementation cases and examine their effects.

• Comprehensive surveying at a road construction site: In a new road construction project, a single smartphone equipped with LRTK carried out everything from control point surveying to 3D scanning of as-built sections and AR verification with the design model. Whereas previously the process—establishing control points with a total station, acquiring point clouds with a 3D laser scanner, and comparing them with the design data on an office PC—used to take several days, after introducing LRTK it was completed in just one day. This is a good example of substantial labor savings and speedup across the entire process because the site personnel themselves could measure and verify on the spot without waiting for a surveying team. It overturned the conventional wisdom of "waiting several days to confirm a few centimeters (a few inches) of as-built condition," and site staff praised it, saying "we no longer have downtime waiting for surveying, and schedule management has become easier."

• Use of AR in heavy equipment operation: At another site, we applied LRTK’s AR functionality to excavation work performed by heavy machinery. We preloaded the planned design lines for excavation into the LRTK app and, during construction, displayed a virtual guideline in AR on the smartphone screen. The operator only needs to move the excavator along the line shown on the screen to excavate to the designed shape and slope. This method enabled accurate work even without installing batter boards (layout marks), contributing to shorter work times and reduced staffing. Because operators can simply dig while watching the line and do not need to be veterans, variations in accuracy due to differing skill levels were also eliminated. As a result, rework was reduced and safety improved, and site supervisors have commented that “even novice operators can be entrusted with the task with confidence.”

• Immediate Measurement and Sharing with One Device per Person: The cost advantages should not be overlooked. Traditionally, assembling a complete RTK surveying system required an investment of several million yen. However, with pocket-sized LRTK devices, introduction is possible at an order of magnitude lower price range, making it realistic to equip sites with one device per person instead of sharing a single expensive instrument. At one civil engineering company, site managers and foreman-level staff carry LRTK units and have begun operating so that each routinely performs surveying and inspections. They measure for themselves immediately when needed and share the results via the cloud with stakeholders, using this to prevent construction errors and optimize schedules. Data sharing has tightened coordination between the site and headquarters, enabling early detection and correction of problems. The agile PDCA cycle that arises from “being able to measure immediately when you want” and “measured data being shared immediately” can be said to be a new on-site operation unique to the smartphone RTK era.

As described above, the effects of introducing smartphone RTK extend across many areas, including work efficiency, accuracy, cost, and safety. Of course, for certain tasks that demand millimeter-level accuracy—such as control-point surveying—there still remains a role for traditional precision instruments and experienced technicians, but for many field operations smartphone RTK delivers practically sufficient accuracy and overwhelming efficiency. Its advantages are clear even when compared with conventional methods, and it is spreading as a powerful tool to accelerate on-site DX.

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

This provides advice for those considering adopting smartphone RTK surveying, covering key points for equipment selection, operational precautions, and initial implementation steps to help you get started smoothly.

• Device and service selection: First, check compatibility between the smartphone and the GNSS receiver you will use. For example, the LRTK series currently supports iPhone and works with an iOS app over 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 take advantage of 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 usage area and needs. If you may use it in mountainous areas outside of network coverage, a model that can receive the Michibiki CLAS signal provides reassurance. Conversely, if you will mainly operate in urban areas, a network RTK–only model may be sufficient. In addition, be sure to consider subscribing to correction information services (such as VRS). Since local government and private distribution services vary by region, select a plan appropriate for your company’s area of use.

• 運用環境と注意点: Before deployment, confirm that smartphone RTK will function adequately in your worksite environment. GNSS depends on a clear view of the sky, so if the location you wish to position has an extremely limited sky view (such as in urban canyons or inside forests), you may have difficulty achieving good accuracy. In such cases, consider choosing the time of day (aiming for when satellite geometry is favorable) or exploring countermeasures such as supplementing with a total station. Also, because smartphone RTK is electronic equipment, battery management is important. Fully charge both the smartphone and the GNSS device, and for long continuous surveys it is advisable to bring a mobile battery. Also be mindful of waterproofing for rainy weather (LRTK terminals are dustproof and waterproof, but put a cover on the smartphone, etc.) and precautions against overheating in the midsummer sun (for example, cool devices in the shade as needed).

• Practice and internal rollout before deployment: Before using it on a live site, first run a trial operation internally or in a safe area. Following the user manual, go through the app’s basic operations, the positioning workflow, and how to save and share data. Test outdoors with good GPS reception to check whether the expected accuracy is achieved and whether the data format is compatible with your company’s drawing/CAD software. Share usage procedures not only with site supervisors and surveyors but also with the workers who will actually use it, and provide a brief training for reassurance. Fortunately, smartphone RTK can be handled like an app, so there are almost no difficult operations, but understanding the positioning principles and precautions will help you respond calmly if problems occur.

• Initial rollout procedure: Once the decision to introduce it has been made, proceed with preparations as follows。 1. Equipment preparation: Purchase or rent the GNSS receiver unit and also obtain holders or poles that can be attached to a smartphone. It is a good idea to start by using 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. Then pair the receiver with the app via Bluetooth and confirm the connection. Also set up the account information for the correction service (VRS) you will use. 3. Outdoor operation check: Go outdoors to an open area, turn on the equipment, and confirm in the app that satellites are being tracked. Begin receiving correction data, and 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 (cm level accuracy (half-inch accuracy)) is achieved without problems, preparation is complete. 4. Field deployment: Finally, start smartphone RTK surveying at actual sites. At first, try it on lower-priority tasks (such as preliminary condition surveys), and gradually expand its application to main tasks such as stakeout and as-built management. Provide feedback on the effects and issues obtained at each site and accumulate know-how within the company.

If you follow the steps above, you should be able to start operating smartphone RTK without any particular difficulties. If you run into trouble, make use of the manufacturer's support and FAQ, and please prioritize safety as you establish the new technology at the job site.

Guide to Introducing LRTK for Simple Surveying

Have you deepened your understanding of the appeal and key implementation points of smartphone RTK surveying? Finally, for those who wish to begin high-precision simple surveying, we will provide guidance on adoption with LRTK in mind.

LRTK was developed with the concept of 'a pocket-sized surveying instrument anyone can use', and is a system that achieves both ease of use and high precision, overturning conventional expectations. Attach the dedicated unit to your smartphone and turn it on, and it will automatically acquire correction information and begin positioning with centimeter-level accuracy (cm level accuracy (half-inch accuracy)) in about 20–30 seconds. Then, simply follow the on-screen instructions and press a button, and accurate latitude, longitude, and elevation are recorded instantly. There is no need for the lengthy setup that used to require erecting a tripod, and its major appeal is that you can take measurements as soon as the idea strikes.

Moreover, the LRTK is compact and lightweight, easy to carry, and also features waterproofing, dustproofing, and shock resistance, so it can be used with confidence even in harsh field environments. The measured data are saved to 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). Its price 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 handling surveying equipment for the first time should be able to master LRTK effortlessly if they are familiar with using a smartphone. The era when on-site surveying can be "quickly done on a smartphone" is just around the corner. Please take this opportunity to consider smartphone surveying with LRTK. The formerly cumbersome surveying tasks will become surprisingly accessible, allowing you to boost on-site productivity while improving quality.

FAQ

Q1. Can't the smartphone's built-in GPS achieve RTK-level high precision? A1. Unfortunately, at present it is not possible to obtain centimeter-level accuracy (half-inch accuracy) with only a smartphone's built-in GPS. A smartphone's standard GPS has an error on the order of several meters (several ft) and cannot access the raw carrier-phase data required for RTK. Therefore, to perform high-precision positioning at the level of a few centimeters (a few in), it is necessary to use an RTK-compatible external GNSS receiver (for example an LRTK terminal). The external device performs the high-precision positioning calculations applying correction information and then passes the results to the smartphone, enabling RTK positioning on the smartphone.

Q2. Is the accuracy of smartphone RTK really reliable? Is it comparable to a total station? A2. Yes — when operated properly, smartphone RTK can provide accuracy that is sufficient for practical use. For example, experiments with LRTK devices have shown that, compared with high-performance GNSS receivers equivalent to the Geospatial Information Authority of Japan's Class 1 standard, positioning errors at the same point differ by only a few millimeters (about 0.04–0.12 in). Compared with the typical accuracy of total-station surveying (several mm–1 cm (several 0.04–0.39 in)) and the accuracy of conventional RTK-GNSS (several cm (several 0.4 in)), smartphone RTK's errors within a few centimeters (within a few 0.4 in) are comparable. It can fully meet the accuracy required at construction sites and in surveying work, so you can use it with confidence without worrying that its small size means inferior accuracy.

Q3. Can smartphone RTK be used in remote mountain areas without cellular signal or during disasters? A3. Even in environments where communications infrastructure is unavailable, smartphone RTK can be operated if conditions are right. The key is the CLAS signal from Michibiki (QZSS). If you have a CLAS-compatible receiver prepared in advance (e.g., the LRTK Pro series), you can receive correction data directly from the quasi-zenith satellites even outside the communication coverage area and continue centimeter-level positioning. In fact, there have been cases in which damage at disaster sites where the mobile network was down was surveyed using CLAS-compatible compact GNSS receivers. However, in environments with absolutely no surrounding line of sight (deep forests or inside tunnels), satellite signals themselves are difficult to receive, so in such cases you will need to re-measure later or supplement with other methods.

Q4. Can accurate positioning be achieved in urban areas with tall buildings or inside forests? A4. In areas lined with high-rise buildings or where trees grow thickly, 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, it is difficult to maintain centimeter-level accuracy. For this reason, in urban areas you should measure at intersections with open sky or where gaps between buildings are wide, and in forests you should measure where trees are sparse or at times when the satellite geometry overhead is favorable. If it remains difficult, consider temporarily measuring that point with a total station or otherwise choosing the appropriate method for the situation. Conversely, in locations with good visibility smartphone RTK is very effective, so we recommend flexibly using it according to the site environment.

Q5. Do I 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 typically subscribe to a commercial VRS distribution service or an RTK service provided by a mobile carrier, and configure the account information in the app to use it (in some regions free correction services operated by local governments are available). On the other hand, if you use 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 UHF radios at the base station was necessary, but correction delivered via networks or satellites does not use additional radio equipment (smartphone communications and satellite reception are permitted for general use). As for surveying qualifications, no qualification is required to operate the equipment itself (however, to use results officially as public survey data they must be conducted under the supervision of a licensed surveyor).

In summary, as long as you have the equipment and a communications environment, anyone can start using smartphone RTK without special licenses.

Q6. Can it be used 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, in the case of LRTK, the unit is attached to an iPhone and used with an app. Support for Android devices must be checked separately, although support may expand in the future. On the other hand, for iPhone, models that support the latest OS are generally usable. However, some features (such as point cloud scanning and camera-based subject positioning) require Pro models equipped with a LiDAR scanner. If possible, using a high-performance model such as the latest iPhone 15 Pro will improve positioning accuracy and the stability of AR displays. Please choose compatible receivers and apps according to the smartphone you own.