In surveying fields, high-precision positioning technology known as "RTK surveying" has made remarkable advances in recent years. In the past, measuring positions with centimeter-level accuracy required expensive, large GNSS receivers, dedicated base stations, and skilled surveyors. But now, simply combining a smartphone with a palm-sized RTK-capable GNSS antenna can achieve equivalent accuracy. A smartphone can turn into a centimeter-class surveying instrument, and on site enable unprecedented measurement and construction management using AR (augmented reality), such as guiding the positions for staking out and layout, projecting 3D design models into real space, and displaying deviations as a color-coded heat map.

This article explains the overview and evolution of RTK surveying, the structure of smartphone RTK and the mechanisms that support centimeter-level accuracy, AR display functions achievable on smartphones, applications to point-cloud scanning and as-built management, cloud-based sharing linking field and office, and the time savings and labor reductions achieved by adoption. Finally, as an example of smartphone RTK surveying that anyone can start easily, we introduce the latest LRTK products.

Table of Contents

• Overview and evolution of RTK surveying

• Structure of smartphone RTK and the mechanism for centimeter-level accuracy

• AR display functions achievable on smartphones (staking out guidance, 3D model projection, as-built heat maps)

• Point-cloud scanning functions and applications to as-built management

• Connecting field and office via cloud sharing

• Effects of smartphone RTK adoption (time savings, labor reduction, etc.)

• Smartphone RTK anyone can start: the future opened by LRTK

• FAQ

Overview and evolution of RTK surveying

RTK (Real Time Kinematic) surveying is a surveying method that uses GNSS satellites to obtain high-precision position coordinates in real time. Regular GPS positioning typically produces errors on the order of several meters (several ft), but RTK exchanges observation data between a reference receiver and a mobile unit (rover) via radio or network and corrects satellite signal error factors in real time, achieving centimeter-level accuracy with horizontal positions of approximately 1-2 cm (0.4-0.8 in) and vertical positions within a few centimeters (a few inches). In the 1990s–2000s, RTK surveying was mainly performed by specialist surveyors using expensive dedicated equipment. However, improvements in satellite positioning accuracy (multi-GNSS and multi-frequency support), the development of electronic reference station networks and VRS network RTK, and services such as Japan’s Quasi-Zenith Satellite System Michibiki providing CLAS (centimeter-level augmentation service) have recently made it easier to perform RTK surveying over wide areas.

Alongside these technological advances, positioning devices have become smaller and less expensive. Previously, fixed base station antennas and large controllers were required, but today comparable positioning can be achieved simply by combining a smartphone or tablet with an ultra-compact RTK-GNSS receiver. For example, some smartphone RTK products (described below) have been verified to have errors on the order of a few millimeters compared with national control points (first-order benchmarks), and their prices are a fraction of those of conventional equipment. Thus, RTK surveying has evolved, and an era has arrived in which not only specialists but also construction managers and field technicians can use it routinely.

Structure of smartphone RTK and the mechanism for centimeter-level accuracy

A smartphone RTK system generally consists of a smartphone (e.g., iPhone or iPad), a small RTK-GNSS receiver that connects to it, and a dedicated app. By using a receiver with an antenna integrated into a smartphone-specific case that can be attached with one touch, the smartphone itself becomes the controller of a high-precision surveying instrument. This receiver supports not only GPS but also GLONASS, Galileo, Michibiki (QZSS), and obtains satellite signals on multi-frequencies such as L1/L5. The raw positioning data acquired are processed in real time by the smartphone app and combined with reference station data or satellite augmentation signals delivered over the network to calculate high-precision coordinates.

The key to achieving centimeter-level accuracy with smartphone RTK is carrier-phase ranging using satellite carrier phases and the use of error correction information. The smartphone receives data via a communications line from networks such as the Geospatial Information Authority of Japan’s electronic reference station network or private correction services, or directly receives Michibiki’s CLAS signals, correcting atmospheric errors and satellite orbit errors. This reduces errors that would be several meters under standalone positioning to a few centimeters. The smartphone also links with its internal IMU (gyros and accelerometers) and electronic compass to consider device attitude and motion during positioning, providing stable results.

With this structure, smartphone RTK receivers are extremely compact, weighing just a few hundred grams and featuring built-in batteries for excellent portability. When necessary, they can be mounted on a monopod or pole and pointed at the point to be measured; pressing a button on the smartphone screen completes the observation. Recorded position data include not only latitude, longitude, and height but also time and the number of satellites tracked. The app automatically performs transformations to Japan’s plane rectangular coordinate system and calculates geoid heights, allowing users to immediately view and use results in familiar coordinate systems on site. Running the same high-precision positioning engine as expensive dedicated equipment on a smartphone and offering it through an interface anyone can use is a major feature of smartphone RTK.

AR display functions achievable on smartphones (staking out guidance, 3D model projection, as-built heat maps)

Smartphone RTK apps include AR functions that support staking out and layout guidance (coordinate navigation). If point data or coordinate values from construction drawings are preloaded into the app, simply pointing the smartphone on site will show the direction and distance to the target position. Arrows or virtual stake markers indicating where to install elements are overlaid on the camera view, so even inexperienced workers are intuitively guided to accurate positions. Staking work that formerly required skilled personnel using total stations can now be handled by one person with just a smartphone.

AR projection of 3D models is another function unique to smartphone RTK. If preconstruction design models (BIM/CIM data, etc.) or completed 3D models are loaded into the smartphone, they can be overlaid on the real scene. Because high-precision position coordinates are obtained, no additional model-to-reality alignment (offset correction) is required, and the 3D model is displayed in the correct position and orientation as if it exists on site. For example, a bridge completion model can be overlaid on terrain point-cloud data, or underground utility models can be shown in AR to visualize excavation hazards. Sharing completion images on site that were hard to understand from drawings or screens greatly aids consensus building and construction planning.

AR display of as-built heat maps is also an innovative feature. Measured as-built 3D data after construction can be compared with the design model and visualized as a color-coded heat map showing differences. Because smartphone RTK ensures that obtained point-cloud data and as-built coordinates are all in global coordinates, a heat map showing design-versus-as-built differences can be automatically generated on the cloud with a few clicks. Loading that heat map into the smartphone makes AR overlay on the real scene possible. For example, color-coding embankment or concrete placement shows high and low areas at a glance, allowing immediate identification of defective construction spots. Previously, detecting problem areas required checking as-built data, extracting locations on drawings, and marking them on site; with AR heat maps, positions are intuitively understood on the spot and corrective work can begin immediately. Mesh size and tolerance ranges (color-coding criteria) for heat maps are user-configurable, enabling flexible inspection and management according to required accuracy. Incorporating AR into daily as-built management dramatically improves the efficiency and reliability of quality control.

Point-cloud scanning functions and applications to as-built management

Leveraging the LiDAR sensors built into iPhones and iPads, smartphone RTK enables easy point-cloud scanning of surrounding structures and terrain. Standalone smartphone scans lacked a positioning reference in the point cloud and often produced distortions such as ground tilting when walking long distances, but smartphone RTK constantly knows its own position with high accuracy and can therefore perform scans with absolute coordinates applied to the point cloud. This eliminates the need to align point clouds with each other or with other survey data and enables stable point-cloud measurements that do not distort even when walking long distances.

On site, a pocket-sized smartphone RTK terminal alone can easily create point clouds of the surrounding terrain and structures, and measure distances between any two points, areas, and volumes on the spot. This can be used routinely for quantity checks of earthwork embankment and excavation, recording the shapes of existing structures, and grasping as-built conditions, without carrying heavy laser scanners or PCs. For example, in bridge inspections you can scan the bridge’s shape as a point cloud and photograph concerning cracks; the photos are then saved on the acquired point cloud with position information. Because anyone can intuitively perform 3D scanning and surveying, field workers themselves can quickly create digital records of current conditions as needed. Acquired point-cloud data can be overlaid with design 3D models in the cloud or used for heat-map analysis, directly supporting as-built and construction management.

Connecting field and office via cloud sharing

Survey data obtained with smartphone RTK can be shared to the cloud from the field instantly. By pressing “sync” or “upload” in the field app, measured points, point clouds, photos, and more are saved to a cloud service via the Internet. Office staff can access the cloud web page in a browser to check coordinates and point-cloud data acquired on site in near real time. They can immediately check the positions and heights of surveyed points in-house or measure distances of surveyed points from the office and provide instructions. Even for large sites, data collected by each person are aggregated on a single map, allowing an overview of current conditions from the office.

Sharing data via the cloud also eliminates the need to hand off USB sticks or manually convert files. Cloud data can be downloaded in CSV or SIMA formats with one click and imported into in-house CAD software as needed. When sharing data with clients or subcontractors, issuing a share link on the cloud allows recipients to view results in a 3D viewer without logging in. Development is also progressing on functions to automatically generate reports on the cloud, making information linkage between field and office even more seamless in the future.

Effects of smartphone RTK adoption (time savings, labor reduction, etc.)

• Reduced working time: Introducing smartphone RTK dramatically shortens the time required for surveying and as-built checks. For example, checking earthwork quantities that formerly required calling a surveying team and doing laser-scanner measurement → data processing → quantity calculations taking more than half a day can be completed in tens of minutes with a smartphone. Staking-out work no longer requires setting up a total station and shuttling back and forth, enabling one person to complete tasks quickly. Cloud sharing also reduces waiting time for information transfer between field and office to nearly zero.

• Addressing labor shortages: In the construction industry, which faces severe technician shortages, smartphone RTK helps operate sites with limited personnel. Field supervisors and workers can perform surveying and as-built checks themselves without relying on specialist surveyors, reducing the frequency of outsourcing or requesting support personnel. Even new or inexperienced staff can obtain results just by following smartphone screen instructions, standardizing previously person-dependent tasks and raising the baseline surveying skills across the organization.

• Labor-saving and reduced workforce: The fact that one person can perform surveying means fewer personnel need to be assigned. Observations and layout tasks that previously required two people can be completed with one smartphone, directly reducing labor costs and improving efficiency. The small, lightweight equipment also reduces the burden of physically demanding surveying work in hot weather or mountainous areas. Reduced equipment transport and long commutes contribute to lower worker fatigue and improved safety.

• Data utilization and automation: Data acquired with smartphone RTK are immediately digitized and accumulated in the cloud, enabling subsequent post-processing and report generation to be automated. Processes such as calculating volumes from point clouds or automatically outputting as-built comparison results can be executed with one button, eliminating manual calculations or drafting. Being able to share accurate data in real time speeds up the construction management PDCA cycle. As a tool for field DX (digital transformation), smartphone RTK contributes to both labor savings and quality improvement in daily operations.

Smartphone RTK anyone can start: the future opened by LRTK

The smartphone RTK technologies and benefits introduced above are already available in market products. For example, the LRTK mentioned in this article is a smartphone RTK solution consisting of an ultra-compact RTK-GNSS antenna attachable to an iPhone and a dedicated app. A single pocket-sized device realizes centimeter-level positioning, point-cloud scanning, AR staking guidance and as-built heat-map display, and cloud sharing.

Thanks to easy-to-use products like LRTK, “one-person, one-device” high-precision surveying is no longer a dream. If anyone on site can quickly perform surveying with a smartphone when needed, the way construction is managed will change significantly. Even amid shortages of experienced surveyors, easy-to-use surveying tools will support sites and enable both productivity gains and quality assurance. Smartphone RTK is already being used for rapid 3D recording of disaster sites by local governments, and its usefulness is attracting wide attention. Smartphone RTK technology will continue to evolve and become commonplace at more sites. If you haven’t adopted it yet, why not start smartphone RTK surveying now? Cutting-edge technology will surely become a powerful helper on your sites.

FAQ

Q: What is RTK surveying? A: It is a technology that corrects GNSS satellite positioning errors and performs centimeter-precision positioning in real time. By making phase observations of GNSS at a reference station and a rover and communicating the difference, high accuracy is achieved. In civil engineering surveying, it is widely used where high precision is required, such as control surveying and as-built management.

Q: What do I need to start smartphone RTK? A: Basically, you need an RTK-capable GNSS receiver and a smartphone (or tablet) that can connect to it. Install the compatible app on the smartphone and attach the receiver to be ready. It is important to have an environment where GNSS correction information can be received via the Internet, or in Japan, an environment where Michibiki CLAS signals can be received. Supported devices vary by product, but generally many are available for iOS devices such as iPhone and iPad.

Q: Is the accuracy really reliable? Can one person survey with a smartphone? A: Yes, with proper use smartphone RTK can achieve high accuracy. In open-sky locations, horizontal errors of 2 cm or less (0.8 in or less) and vertical accuracy on the order of a few centimeters (a few inches) can be expected. Comparative tests with dedicated high-precision GNSS equipment have shown almost no difference. One-person staking guidance is also feasible because the smartphone’s AR display navigates the user. In sites with labor shortages, the ability to perform tasks solo is a major advantage.

Q: What about places where satellites cannot be received? A: In environments where GNSS signals are hard to reach, such as urban canyons between buildings or dense forests, smartphone RTK positioning is unfortunately difficult. In such cases, traditional terrestrial surveying instruments like total stations or combinations of basic GNSS positioning with other methods may still be necessary. However, multi-GNSS support and Michibiki utilization have improved satellite tracking performance compared to older equipment, so positioning is possible in many locations with somewhat open skies. There are cases in mountainous areas where conventional methods produced meter-level errors but smartphone RTK has performed adequately.

Q: In what situations can it be used? A: It is used in many aspects of civil engineering and construction. Examples include as-built surveying and earthwork quantity management at development sites, staking and batter board setup in road works, as-built checks in bridge and tunnel works, and recording damage at disaster sites—any scenario requiring high-precision location information. Shifting surveying tasks formerly handled by specialists to field staff enables faster on-site work and contributes to schedule reduction and quality assurance. Smartphone RTK will increasingly become a standard tool across diverse field situations.