Introduction to Smartphone Surveying: How RTK Works and Starting High-Precision Positioning with LRTK

In recent years, smartphone surveying (surveying methods utilizing smartphones) has been attracting attention. Traditionally, surveying required specialized surveying equipment and multiple people, but nowadays combining smartphones with GNSS (Global Navigation Satellite System) technology makes it easy to obtain high-precision location information. In particular, leveraging RTK (Real-Time Kinematic), a high-precision GNSS positioning technology, on smartphones enables position measurements with errors of just a few centimeters—an accuracy previously unthinkable. This article explains the basics of GNSS and RTK, the differences from conventional surveying, and the benefits of using RTK in smartphone surveying. It also introduces how to get started with smartphone surveying using LRTK, a cutting-edge high-precision positioning solution, and provides concrete use cases. By reading to the end, you will gain clear knowledge and steps to begin simple high-precision surveying with a smartphone.

Basics of GNSS and RTK

GNSS is a general term for global navigation satellite systems that use artificial satellites and includes multiple satellite positioning constellations such as GPS (United States), GLONASS (Russia), Galileo (Europe), and Michibiki (Japan’s quasi-zenith satellite). A GNSS receiver receives radio signals transmitted from multiple satellites and calculates its current position (latitude, longitude, altitude) from the distance information. However, ordinary GNSS positioning can have errors on the order of several meters due to atmospheric effects, satellite clock errors, and so on. The GPS in smartphones is a type of GNSS, but it typically has position errors of about 5–10 m, which is insufficient for accurate surveying.

RTK (Real-Time Kinematic) positioning is the technology that corrects these errors and achieves centimeter-level accuracy. In RTK, both a base station (reference point) installed at a known accurate position and a rover (mobile receiver) that moves while being positioned simultaneously receive GNSS satellite signals. The base station compares its known accurate position with the satellite measurement information to calculate the error amount, and it transmits that correction data to the rover in real time. By using the received correction information, the rover can improve positioning results that would otherwise be off by several meters to an accuracy of a few centimeters. RTK uses the carrier phase of the satellite signal, which has a very short wavelength, enabling millimeter-order ranging accuracy and thus dramatically improving final position accuracy. Such real-time high-precision positioning is being used in a wide range of fields, including civil engineering surveying, agriculture, and autonomous driving.

Differences from Conventional Surveying

There are several major differences between traditional surveying methods and GNSS surveying using smartphones (smartphone surveying). In traditional surveying, optical instruments such as total stations and levels were used, and surveyors aimed at targets to measure distances and angles. This required a two-person team with a surveying instrument and a prism holder, and line-of-sight between survey points had to be maintained, resulting in considerable time and effort. Even when using high-precision GNSS surveying equipment, cases existed where a stationary base station and a rover were set up and post-processing was required.

The main differences are summarized below.

• Number of people required: Traditionally, work was typically done by two or more people, but smartphone surveying can be completed by one person.

• Line-of-sight requirement: Total stations require direct line-of-sight between the instrument and the prism, but GNSS surveying can position through obstacles as long as the sky above is open.

• Work efficiency: Traditional methods required time for instrument setup and point-by-point readings and recording, whereas RTK-based smartphone surveying allows you to move to the point you want to measure and immediately obtain high-precision coordinates.

• Positioning coordinates: Traditionally, relative positions from control points were measured and later converted to a reference system, but GNSS provides absolute coordinates such as those in a global geodetic system from the start.

• Equipment and cost: High-performance optical instruments and dedicated GNSS terminals were expensive and heavy, but smartphone surveying uses a handheld smartphone and a compact GNSS receiver, making it low-cost and lightweight.

In this way, RTK-enabled smartphone surveying reduces labor and improves efficiency compared to conventional methods, significantly lowering the barrier to fieldwork. In particular, the ability to obtain positioning results in real time is a major advantage because data can be checked and additional measurements can be made on site.

Benefits of Using RTK in Smartphone Surveying

Combining a smartphone with RTK technology—“smartphone surveying”—offers various benefits not found in traditional methods. Here are some of the main advantages.

• Improved efficiency and reduced labor: Because surveying can be done easily by one person, personnel allocation can be optimized. For example, on a large site, a person can walk around with a smartphone and take position measurements without the need for multiple people to perform heavy work.

• Real-time positioning: RTK provides high-precision coordinates on-site instantly, allowing work to proceed while checking measurement results in real time. Additional measurements or retries can be decided on the spot, reducing backtracking.

• High accuracy: Smartphone surveying achieves centimeter-level accuracy that ordinary smartphone GPS cannot reach. It can provide reliable results for tasks requiring precision, such as topographic surveying and structure installation.

• Cost reduction: Instead of purchasing expensive surveying equipment or hiring specialist contractors, you can use your smartphone and relatively inexpensive GNSS receiver devices, reducing initial investment and maintenance costs.

• Easy data utilization: Obtaining data with a smartphone makes it easy to upload directly to the cloud or import into drawings and GIS software, enabling digital use of the data. Recording in paper field books and manual transcription are no longer necessary, reducing human errors.

• Multifunctional applications: By combining a smartphone’s camera and sensors, you can create photo-tagged survey point records, overlay designs on the site using AR (augmented reality), or acquire 3D point clouds via LiDAR scanning, allowing versatile applications beyond simple point surveys.

Thus, smartphone surveying is not only high-precision and low-cost but also highly compatible with digital technologies, making it a key technology to support DX (digital transformation) in future construction and surveying sites.

Features and Accuracy of LRTK

LRTK is a state-of-the-art high-precision positioning system developed to make RTK positioning easy to perform with a smartphone. It consists of a compact GNSS receiver that fits in your pocket (LRTK device), a smartphone app, and cloud services, and this combination completes RTK high-precision positioning. The LRTK device weighs about 165 g and, despite being smartphone-sized with a thickness of about 1 cm (0.4 in), receives signals from multiple satellite positioning systems (GPS, Michibiki, etc.) and performs RTK computations to achieve positioning accuracy of about horizontal ±1–2 cm (±0.4–0.8 in) and vertical ±3 cm (±1.2 in). That level of accuracy is comparable to first-class surveying GNSS equipment, and experiments have confirmed that when measuring the same point as a professional receiver, differences are only on the order of a few millimeters.

LRTK pursues ease of use as well as high accuracy. Reference point data for base stations are automatically acquired via the internet, so users do not need to set up their own base station. By turning on the LRTK device outdoors and connecting it to a smartphone, you can obtain an RTK “Fix” solution (a solution with an error of a few centimeters) in about 20 seconds and start surveying immediately. The measured latitude, longitude, and height data can be converted and recorded into any coordinate system, such as the plane rectangular coordinate system, and the app automatically handles coordinate transformations that previously required manual processing. Acquired data can also be synchronized to the cloud in real time, making it easy to immediately check and share field measurement results from the office. Compact, high-performing, and optimized for fieldwork, LRTK is a strong option for those who want to start high-precision smartphone surveying.

How to Implement LRTK and Required Equipment

This section explains the equipment needed to implement LRTK and start smartphone surveying, and the initial setup flow.

Required equipment: Basically, you only need the LRTK device, a high-precision GNSS receiver, and a compatible smartphone (currently supported on iPhone) to perform positioning. Install the LRTK app on your smartphone, connect the smartphone and the LRTK device via Bluetooth or similar, and if you have an internet-connected environment, no additional base station equipment is required. To more accurately pinpoint survey points, it is recommended to mount the LRTK device and smartphone on a commercially available monopod (pole) or a dedicated stand. The LRTK starter kit includes a pole (monopod) and a pointed tip for stable measurement, allowing you to firmly place the device on ground markers for measurements.

Implementation and setup steps:

• Prepare the LRTK device: Turn on the power of the LRTK device and confirm that the battery level is sufficient (charge if necessary).

• Install the app: Download and install the dedicated LRTK app on your smartphone. On first launch, register as a user (create an LRTK Cloud account) and log in to the app.

• Connect the device and smartphone: Use the “device connection” function in the app to pair the smartphone and the LRTK device. Select your device from the list of nearby LRTK devices; when connected successfully, the device will notify you with a sound or LED.

• Operation check: In an outdoor area with a clear view of the sky, verify that the app shows satellite reception (number of satellites and current positioning mode). In the initial state, RTK corrections are not applied, so accuracy will be on the order of ± a few meters, but high-precision positioning is achieved in the next step.

• Start RTK corrections: Start receiving correction information from a base station within the app. LRTK will automatically begin obtaining correction data over the internet, and in about 20–30 seconds the positioning mode will switch to “Fix.” Once in Fix, centimeter-level RTK positioning is available.

That completes the initial setup. Once setup is finished, you can simply turn on the device and connect the app on site to use high-precision positioning.

LRTK Operation Procedures

Here are basic operation procedures for conducting surveys on site with LRTK. The LRTK system can be operated intuitively via a smartphone app and provides functions to meet various surveying needs.

• Point surveying (measuring points): Place the LRTK device at the point you want to measure and press the positioning/record button in the smartphone app to record high-precision coordinates for that point. If necessary, you can average measurements over several seconds before recording to further improve the accuracy per point. You can assign names and notes to survey points and attach photos, making later management easy to understand.

• Stakeout and layout: If the coordinates of control points or planned installation points are known in advance, input those coordinates into the app for guidance. The smartphone screen displays the direction and distance to the target point in real time, so move the device on site while watching the display and find the point where the distance becomes zero. The app can provide guidance with sound or AR displays as needed, enabling even a single person to accurately locate stakeout positions.

• Continuous surveying and area measurement: By continuously recording points while walking, you can perform longitudinal and cross-sectional surveys of terrain or survey site boundaries. From trajectory data automatically recorded at fixed intervals, you can later create plan views or calculate area and distance. Distances and areas that were traditionally measured by tape or calculated manually can be automatically computed on site with smartphone surveying, improving efficiency.

• Data storage and sharing: After measurements are complete, synchronize the saved data in the app to the cloud. From an office PC, access the cloud over the internet to immediately review field survey data (coordinate lists, photos, notes, trajectories, etc.). You can download data in CSV or DXF formats as needed and easily import them into your CAD drawings or GIS. There is no need to bring back paper documents, shortening data organization time.

The intuitive ability to perform these operations with a single smartphone is a major attraction of smartphone surveying with LRTK. Because surveying on site and data sharing are seamlessly completed, the previously cumbersome tasks are greatly simplified.

Application Examples of Smartphone RTK

Finally, here are some application examples of how high-precision positioning using smartphones and RTK is useful in the field.

• Rapid surveying at disaster sites: Smartphone RTK is useful for quickly surveying damage after earthquakes or heavy rain. Even in disaster areas where heavy machinery cannot enter, a person carrying a smartphone and an LRTK device can measure collapsed terrain in a short time. In one local government case, LRTK was used to rapidly capture terrain data at a landslide site and aided in planning recovery measures.

• As-built management on construction sites: On roads and land development construction sites, verifying that construction matches design plans is essential. Using smartphone RTK, construction personnel can measure the heights of embankments and cut slopes and the positions of structures themselves and immediately check deviations from design values on site. Because inspections that traditionally required surveyors can be done in real time, this helps prevent rework and shortens construction schedules.

• Recording locations of infrastructure facilities: Accurately recording locations of infrastructure such as water pipes, utility poles, and gas valves is important for maintenance and inspection. With smartphone RTK, you can instantly measure and database the latitude, longitude, and height of each facility. Photos and notes can be attached on site, allowing detailed information to be shared without revisiting the site.

• Design and construction support with 3D scanning and AR: Combining smartphone cameras or LiDAR with RTK positioning makes 3D site scanning and AR visualization easy. For example, you can scan building interiors with a smartphone to obtain high-precision point cloud data or overlay a planned structure model onto live site imagery via AR to share with construction stakeholders. High-precision position information allows these advanced technologies to be used without error, promoting DX at worksites.

Conclusion: Start High-Precision Simple Surveying with LRTK

The advent of smartphone surveying is set to dramatically change the world of surveying. By understanding GNSS and RTK and leveraging easy-to-use, high-precision tools like LRTK, tasks that once required specialists can now be performed by your own team. The ability to obtain centimeter-level position information instantly on a smartphone will dramatically improve the efficiency and quality of construction and surveying work. Expensive equipment and extensive preparations are no longer required. Take this opportunity to introduce LRTK and experience the benefits of high-precision positioning started with a smartphone. Smartphone surveying is worth learning not only for young personnel familiar with smartphone operation but also for mid-career technicians experienced in traditional methods as a valuable new skill. Let’s pioneer an era where surveying can be completed with a single smartphone, together with LRTK.