In the field of surveying, the high-precision positioning technology known as RTK surveying has made remarkable advances in recent years. In the past, achieving centimeter-level positional accuracy required expensive, large GNSS receivers, dedicated base stations, and skilled surveyors to operate them. But now, simply combining a smartphone with a palm-sized RTK-capable GNSS antenna can achieve equivalent accuracy. A smartphone can be turned into a centimeter-class surveying instrument, enabling unprecedented measurement and construction management using AR (augmented reality), such as position guidance for staking out and layout marking, projection of 3D design models onto the real world, and color-coded heatmap displays showing as-built differences.

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 with a smartphone, applications to point cloud scanning and as-built management, cloud sharing to link the field and office, and the effects of adoption such as time savings and labor reduction. Finally, as an example of smartphone RTK surveying that anyone can easily start with, we introduce the latest LRTK product.

Table of contents

• Overview and evolution of RTK surveying

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

• AR display functions achievable with a smartphone (staking-out guidance, 3D model projection, as-built heatmap)

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

• Connecting the field and office via cloud sharing

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

• Smartphone RTK anyone can start with: 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. Ordinary GPS positioning can have errors on the order of meters, but RTK exchanges observation data between a reference receiver and a mobile unit (rover) via radio or network and corrects satellite signal error sources in real time, achieving centimeter-level accuracy — roughly 1–2 cm horizontally and a few centimeters vertically. From the 1990s through the 2000s, RTK surveying was mainly performed by specialists using expensive dedicated equipment. However, improvements in satellite positioning accuracy (multi-GNSS and multi-frequency support), the development of network RTK such as electronic reference point networks and VRS, and services like CLAS (centimeter-class augmentation service) provided by Japan’s QZSS "Michibiki" have made it easier to perform RTK surveying over wide areas in recent years.

Along with these technological advances, GNSS equipment has become smaller and less expensive. Whereas fixed base station antennas and large controllers were once required, it is now possible to achieve equivalent positioning by combining a smartphone or tablet with an ultra-compact RTK-GNSS receiver. For example, smartphone RTK products described later have demonstrated errors on the order of a few millimeters compared to national geodetic control points (first-order), while costing a fraction of traditional equipment. In this way, 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 typically consists of a smartphone (e.g., an iPhone or iPad), a small RTK-GNSS receiver that connects to it, and a dedicated app. By using a receiver integrated with an antenna that can be attached to a dedicated smartphone case with one touch, the smartphone itself becomes the controller of a high-precision surveying instrument. This receiver supports multiple satellite constellations — not only GPS but also GLONASS, Galileo, and QZSS (Michibiki) — and acquires satellite signals on multi-frequencies such as L1/L5. The raw positioning data obtained are processed in real time by the app on the smartphone, which combines them with reference station data or satellite augmentation signals delivered over the network to compute high-precision coordinates.

The key to achieving centimeter-level accuracy with smartphone RTK is carrier-phase based ranging and the use of error correction information. The smartphone receives data via communication lines from the Geospatial Information Authority of Japan’s electronic reference point network or from commercial correction services, or directly receives QZSS Michibiki’s CLAS signals, to correct atmospheric and satellite orbit errors. This reduces standalone positioning errors of several meters down to a few centimeters. In addition, integration with the smartphone’s built-in IMU (gyros and accelerometers) and electronic compass accounts for device attitude and movement during positioning to provide stable results.

With this structure, smartphone RTK receivers are extremely compact — weighing only a few hundred grams — and include internal batteries for excellent portability. If necessary, they can be mounted on a monopod or pole and simply pointed at the point to be measured, with observations completed by tapping a button on the smartphone screen. Recorded position data include not only latitude, longitude, and height but also time and the number of satellites tracked. The app automatically converts coordinates into Japan’s plane rectangular coordinate system and computes geoid height, so results can be checked and used on-site in familiar coordinate systems. Running a positioning engine equivalent to that of expensive dedicated equipment on a smartphone and providing it through an interface anyone can use is a major characteristic of smartphone RTK.

AR display functions achievable with a smartphone (staking-out guidance, 3D model projection, as-built heatmap)

Smartphone RTK apps include AR functions that support staking-out and position 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 place elements are overlaid on the camera view, so even inexperienced workers are intuitively guided to the correct location. Tasks that once required skilled operators with total stations for staking out can now be performed by one person with just a smartphone.

3D model AR projection is another unique function of smartphone RTK. If design models (BIM/CIM data, etc.) or 3D models of the finished state are loaded into the smartphone, they can be displayed over the real scene on-site. Because high-precision position coordinates are available, model-to-reality alignment (offset correction) is unnecessary, and 3D models appear in the correct position and orientation as if they exist there physically. For example, one can overlay a bridge’s completion model on terrain point cloud data or display underground utility models in AR to visualize excavation hazards. Sharing the completed image on-site with stakeholders — which is often hard to grasp from drawings or screens — is extremely effective for consensus building and construction planning.

The as-built heatmap AR display is also an innovative feature. By comparing measured 3D as-built data with the design model and color-coding the differences as a heatmap, disparities can be visualized. Because smartphone RTK collects point clouds and as-built coordinates all in global coordinates, a cloud-based workflow can automatically generate a heatmap of design vs. as-built differences with just a few clicks. Loading the generated heatmap into the smartphone enables AR overlay on the actual site view. For example, color-coding embankment or concrete placement as-built data instantly highlights high and low areas so construction defects can be identified immediately. Traditionally, one would check as-built data, mark problem locations on drawings, and then mark them on-site — AR heatmaps allow intuitive on-site recognition of positions so remedial work can begin right away. Mesh size and tolerance ranges (color-coding criteria) of heatmaps can be set arbitrarily, 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 function and applications to as-built management

By leveraging the LiDAR sensor built into iPhone or iPad, smartphone RTK enables easy point cloud scanning of surrounding structures and terrain. Standalone smartphone scans lack a positioning reference in the point cloud and can suffer distortions such as ground tilt after walking long distances, but smartphone RTK constantly determines absolute position with high accuracy, allowing scans to be performed while assigning absolute coordinates 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 over long distances.

In the field, a pocket-sized smartphone RTK device can quickly convert surrounding terrain and structures into point clouds, allowing on-the-spot measurement of distances between arbitrary points, areas, and volumes. It can be used routinely for earthwork volume checks, recording shapes of existing structures, and as-built verification without carrying heavy laser scanners or PCs. For instance, during bridge inspections one can scan the bridge geometry while photographing suspicious cracks; the photos are saved with position information on the acquired point cloud. Because anyone can intuitively perform 3D scanning and surveying, field workers themselves can rapidly create digital records of current conditions as needed. The acquired point cloud data can then be overlaid with design 3D models in the cloud or used for heatmap analysis, directly supporting as-built management and construction control.

Connecting the field and office via cloud sharing

Surveying data collected with smartphone RTK can be shared to the cloud from the field instantly. By tapping “sync” or “upload” in the field app, measured points, point clouds, photos, and other data are saved to a cloud service via the internet. Office staff can access the cloud web page in a browser to view coordinates and point cloud data acquired on-site in near real time. It is possible to immediately check the positions and heights of measured points within the office or measure distances on points taken in the field and provide instructions — even when the site is large, data collected by each person aggregates on a single map so the office can remotely get an overview of current conditions.

Sharing data via the cloud also eliminates the need to hand over USB drives or perform manual file conversions. As needed, cloud data can be downloaded in CSV or SIMA formats with one click and imported into in-house CAD software. When sharing data with clients or subcontractors, issuing a share link on the cloud lets recipients view results in a 3D viewer without logging in. Development is also underway for features that automatically generate reports in the cloud, further streamlining information flow between the field and office.

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

• Reduced work time: Introducing smartphone RTK greatly shortens the time required for surveying and as-built checks. For earthwork volume checks, tasks that used to require calling a survey team for laser scanner measurement → data processing → quantity calculation and take more than half a day can be completed in minutes with a smartphone. Staking out also becomes faster because setting up and transporting total stations is unnecessary, and one person can complete tasks in a short time. Cloud sharing likewise reduces wait times for information transfer between field and office to near zero.

• Countermeasure for labor shortages: In the construction industry where staffing shortages are severe, smartphone RTK helps run sites with fewer people. Field supervisors and workers can perform surveying and as-built checks themselves without relying on specialist surveyors, reducing the need to arrange outsourcing or temporary personnel. Even new or inexperienced staff can obtain results by following smartphone screen instructions, helping to standardize tasks that were previously person-dependent and raising the overall level of surveying skills across the organization.

• Labor-saving and workforce reduction: The ability for one person to perform surveying means fewer workers need to be allocated. Tasks that formerly required two people working as a pair for observations or layout marking can be completed with a single smartphone, directly reducing labor costs and improving efficiency. Equipment’s small, lightweight nature also reduces the burden of physically demanding surveying work in hot weather or mountainous areas. Reduced equipment transport and long commutes also help decrease worker fatigue and improve safety.

• Data utilization and automation: Data acquired with smartphone RTK are immediately digitized and stored in the cloud, enabling automation of subsequent post-processing and report generation. Processes such as computing volumes from point clouds or automatically outputting as-built comparison results can be executed with a single button, eliminating manual calculations or redrafting of drawings. Being able to share high-accuracy data in real time accelerates the PDCA cycle in construction management. As a tool for on-site DX (digital transformation), smartphone RTK contributes both to labor saving and quality improvement in daily operations.

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

The smartphone RTK technologies and benefits introduced so far are already available in commercial products. For example, the LRTK mentioned in this article is a smartphone RTK solution consisting of an ultra-compact RTK-GNSS antenna that attaches to an iPhone and a dedicated app. A single pocket-sized device delivers centimeter-level positioning, point cloud scanning, AR staking-out navigation and as-built heatmap display, and cloud sharing.

Thanks to easy-to-use products like LRTK, “one device per person” high-precision surveying is no longer a dream. If everyone on site can quickly perform surveying with a smartphone whenever needed, the way construction is managed will change dramatically. Even amid a shortage of skilled surveyors, surveying tools anyone can easily use will support sites and enable both productivity improvements and quality assurance. Smartphone RTK is already being used, for example, by municipalities for rapid 3D recording of disaster sites, 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 is sure to become a powerful helper on your site.

FAQ

Q: What is RTK surveying? A: It is a technique that corrects GNSS satellite positioning errors to perform centimeter-accurate positioning in real time. Carrier-phase observations are made at a reference station and a rover, and differential correction is communicated to achieve high accuracy. It is widely used in civil engineering surveying for tasks requiring high precision, such as control point surveys 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 also important to have an environment where GNSS correction information can be received via the internet or, within Japan, where Michibiki’s CLAS signals can be received. Supported devices depend on the product, but many solutions are available for iOS devices such as iPhone and iPad.

Q: Is the accuracy really reliable? Can I perform surveying alone with a smartphone? A: Yes — when used properly, smartphone RTK can achieve high accuracy. In open-sky conditions you can expect horizontal errors under 2 cm and vertical accuracy on the order of a few centimeters. Comparative tests with dedicated high-precision GNSS equipment have shown nearly indistinguishable results. One-person staking-out guided by the smartphone’s AR display is also feasible and effective, making smartphone RTK a major advantage for sites with labor shortages.

Q: What if satellites cannot be received? A: In environments where GNSS signals are hard to receive, such as urban canyons between buildings or dense forests, smartphone RTK will also struggle. In such cases, ground-based surveying instruments like total stations or a hybrid approach combining simple GNSS positioning may still be necessary. However, multi-GNSS support and Michibiki utilization have improved satellite reception compared to older devices, so positioning is often possible in areas with even modest sky view. There are cases where smartphone RTK successfully handled situations in mountainous areas that previously produced meter-level errors.

Q: In what situations can it be used? A: It is applicable across many civil and architectural construction scenarios. Examples include as-built surveys and earthwork volume management at development sites, staking-out and batter board placement in roadworks, as-built verification in bridge and tunnel construction, and recording disaster site damage — essentially any scene that requires high-precision location information. By enabling field personnel to conduct surveying that was previously outsourced, smartphone RTK contributes to shorter construction schedules and improved quality. Its use is expected to become increasingly widespread across diverse sites.