RTK Surveying Evolving with Cloud Integration: A New Proposal — Smartphone-Only + Centimeter Accuracy (half-inch accuracy)

Table of Contents

• What is RTK surveying?

• Challenges of traditional RTK surveying

• Evolution of RTK surveying through cloud integration

• A new era of surveying completed on a smartphone

• Achieving centimeter accuracy (half-inch accuracy) with smartphones

• Possibilities for surveying expanded by cloud utilization

• A new simple surveying proposal using LRTK

• FAQ

In recent years, digital transformation (DX) that leverages digital technologies has been advancing rapidly in construction and surveying sites. Among these, RTK surveying using GPS and GNSS satellites has attracted attention as a method capable of positioning with unprecedented high accuracy. RTK stands for Real Time Kinematic, a technique known in Japanese as “dynamic interferometric positioning.” By performing real-time error correction, it can reduce positioning errors that are several meters (several ft) with standalone GPS down to several centimeters (several in), making it widely used in civil engineering and the construction industry.

Traditionally, RTK surveying required specialized GNSS surveying equipment and installation of base stations (reference stations), but recently it has been evolving into a more user-friendly form through cloud integration via the Internet and the use of smartphones. This article starts with the basics of RTK surveying, explains efficiency gains from linking with cloud services, and describes a new surveying style that can be completed with just a smartphone. Finally, as a new proposal that makes centimeter-level accuracy easy to achieve, we introduce a simple surveying method using LRTK. Based on the latest trends in high-precision positioning technology, let’s explore new surveying styles that overturn conventional wisdom.

What is RTK surveying?

RTK surveying is a technique that uses two GNSS receivers—a base station (reference station) and a rover—to perform high-precision positioning in real time. With a single receiver performing normal GNSS positioning (standalone positioning), positional errors of several meters (several ft) occur due to satellite signal errors. In RTK, however, the base station is placed at a known coordinate, and correction data obtained from it is sent to the rover to cancel out satellite positioning errors in real time.

With this mechanism, the rover’s receiver (on the point to be measured) applies the base station’s correction information to its own positioning data and can determine its position within an error range of several centimeters (several in). For example, in situations where normal GPS would produce an error of around 5 m (16.4 ft), RTK surveying can suppress the error to about 2–3 cm (0.8–1.2 in). The strict accuracy standards required in civil engineering work can be met on site immediately by using RTK.

Challenges of traditional RTK surveying

Although RTK surveying enables high-precision positioning, traditional operations had several challenges. First, specialized surveying equipment was required. Equipping a full set—RTK GNSS receivers, antennas, radios, controllers—required a significant investment, and the equipment was large and cumbersome to carry. Operating the equipment also required specialized knowledge and experience, and there were situations where it was difficult to achieve the required accuracy without skilled personnel.

Furthermore, it was common to set up a base station on site, which required preparing a known point or performing base station setup work for each site. When the base station and rover communicated directly by radio, the radio range was limited, and on large construction sites repeaters or moving the base station could be necessary. There was also the problem that the effectiveness of the correction diminished as the distance from the base station increased, reducing accuracy.

On the other hand, using a communication network with “network RTK” (Ntrip) can eliminate the need to prepare your own base station, but it requires an internet connection and subscription to a correction information service. In locations with unstable communication environments, there was a risk that correction data could not be received and positioning would be interrupted. In addition, the traditional workflow of bringing acquired survey data back to the office for analysis and drafting made it difficult to share results in real time, which was inefficient.

Evolution of RTK surveying through cloud integration

The use of the Internet and cloud services has significantly advanced RTK surveying operations. A representative example is cloud distribution using network RTK. By using services that distribute data from reference stations (continuous operating reference stations) maintained in various regions via the Internet, surveyors can access correction information on the cloud through smartphones or rover receivers and achieve centimeter-level positioning that is stable over wide areas. This is revolutionary in that it eliminates the need to set up your own base station and ensures accuracy anywhere on site.

Furthermore, cloud integration is changing how positioning data itself is handled. Previously, coordinate data and survey results obtained on site were brought back for analysis and drafting on a PC. Now, data can be automatically saved and shared on the cloud simultaneously with measurement, allowing real-time sharing with the office and other team members. For example, uploading point cloud data observed on site or photo-attached survey records to the cloud enables office personnel to immediately review the content and provide feedback. This can reduce rework and enable quicker decision-making.

Using survey platforms on the cloud, services have emerged that automatically perform the necessary calculations and drafting from data measured on site. Cloud functions that instantly compute distances, areas, and volumes and visualize results in a browser make it possible to obtain survey outcomes on site. By offloading analysis processes that previously required specialized software to the cloud, the on-site burden can be reduced and efficiency improved.

A new era of surveying completed on a smartphone

Recent smartphones have seen dramatic improvements in processing power and sensor performance, and solutions that use smartphones in surveying have emerged. Smartphone-only surveying refers to a surveying style in which the entire workflow—from positioning to data recording to analysis—can be done using only a smartphone. Without carrying dedicated surveying equipment, by attaching a compact high-precision GNSS receiver to a smartphone and using a dedicated app, positioning with centimeter-level accuracy comparable to traditional equipment has become possible. By accessing correction information services via mobile networks or utilizing high-performance GNSS chips built into smartphones, a single mobile phone can serve the role of a surveying instrument.

The advantages of using a smartphone are not limited to portability. Intuitive touch-operated apps improve the operability of surveying and make it easier for beginners to handle. For instance, you can simply point the smartphone at the point to be measured and tap a button to record coordinates, or automatically tag photos taken on site with positioning information and save them. Tasks that used to be performed with separate devices—“measure,” “record,” and “verify”—now complete seamlessly on a single device, dramatically improving operational efficiency.

In addition, smartphone-specific functions can be applied to surveying. Using the camera or LiDAR scanner (on supported models) to capture the surroundings as point cloud data and adding position information in real time enables instant generation of detailed 3D models and terrain data of the site. With AR (augmented reality) display on the smartphone screen, you can overlay drawings or points to be measured on the real view for confirmation. This makes it possible to intuitively perform tasks such as stakeout positions and confirming locations of buried objects while looking at the screen. Knowing the positions of buried objects in advance also reduces the risk of accidentally damaging underground structures.

Achieving centimeter accuracy (half-inch accuracy) with smartphones

The key to smartphone-based surveying is how to ensure centimeter-level positioning accuracy. Fortunately, technologies for combining high-precision GNSS with smartphones have advanced. Some commercial smartphones can receive multiple GNSS frequency bands such as L1 and L5, enabling the more precise ranging needed for RTK positioning. However, standalone smartphones generally have limitations in antenna performance, so in practice it is effective to use a dedicated compact GNSS receiver (an external device) to achieve centimeter accuracy.

To achieve centimeter accuracy (half-inch accuracy), correction information in addition to GNSS measurement data is indispensable. If the GNSS receiver connected to the smartphone has Ntrip client functionality, it can obtain correction data from a regional reference station network via the mobile network. In Japan, you can also use the quasi-zenith satellite “Michibiki” centimeter-class positioning augmentation service (CLAS) to improve positioning accuracy even in locations without an Internet connection. In this way, the combination of smartphone + high-precision GNSS + correction information service makes it possible to achieve accuracy that previously could only be obtained with fixed surveying equipment using palm-sized devices.

Of course, to consistently obtain centimeter accuracy, an environment where satellite signals can be received well is necessary. In urban areas surrounded by high-rise buildings or regions with many trees, GNSS signals can be blocked or multipath (reflections) can cause errors, so observation positions and timing need to be adjusted in such cases. However, the latest smartphone surveying systems let you check satellite reception status and FIX solutions (and the difference from float solutions) on the screen, enabling quality control such as taking measurements at times when accuracy can be ensured. The fact that software supports accuracy management that professional surveyors used to perform empirically is also an advantage of smartphone surveying.

Possibilities for surveying expanded by cloud utilization

New surveying methods that combine smartphones and the cloud have made a variety of previously difficult tasks possible. For example, “3D surveying” that acquires terrain and structures as dense point cloud data can be achieved by scanning with a smartphone without expensive laser scanners or drones. Since image analysis and data integration are performed on the cloud to generate precise 3D models in a short time, these can be used for creating topographic maps and construction progress/quality control. Surveying and measurement work that used to be outsourced to specialized contractors can now be easily performed by on-site staff, leading to cost reduction and shorter lead times. The spread of these technologies makes it easier for small and medium-sized construction companies and surveying offices to adopt the latest high-precision surveying.

Also, centralizing data on the cloud makes secondary use and collaborative work with survey data smoother. It becomes easy to link with GIS or CAD software to reflect data in design and construction planning, or to accumulate past survey data to track changes over time. Multiple stakeholders sharing the same up-to-date data reduces rework and mistakes caused by mismatched understanding. If clients and designers can check 3D models on the cloud remotely and grasp site conditions in real time, decision-making speed will improve.

Moreover, in the context of the Ministry of Land, Infrastructure, Transport and Tourism’s “i-Construction” initiative and the trend of construction DX, cloud integration and smartphone surveying are important pieces. ICT-based construction requires managing everything digitally, from pre-construction site understanding to construction-stage quality control and post-completion records. In such cases, the combination of smartphone surveying, which can acquire high-precision data easily on site, and cloud services that can instantly share and analyze data is highly effective. In an industry facing labor shortages, these technologies—enabling efficient surveying by one person—are expected to greatly contribute to productivity improvement and labor savings on site.

A new simple surveying proposal using LRTK

As discussed above, RTK surveying has evolved dramatically through cloud integration and smartphone use. The solution that allows this new surveying style to be easily practiced on site is LRTK. LRTK is a system composed of a smartphone-integrated high-precision GNSS receiver and cloud services, designed so that even without specialized equipment a single person can perform centimeter-accuracy (half-inch accuracy) surveying.

Specifically, a small GNSS unit (with built-in battery and antenna) that can be attached to a smartphone is used for positioning, and a dedicated app automatically uploads the position information and acquired photos and point cloud data to the LRTK cloud. For example, simply walking while pointing the camera can scan wide areas of terrain and create high-precision 3D point cloud models with coordinates. Not only are coordinates of measured points recorded, but distance, area, and volume calculations can be performed on the cloud immediately, enabling you to obtain necessary measurement results on site. Acquired data is shared in real time, greatly reducing the time spent returning to the office for data verification and drafting. Since outputs can be produced in a form that complies with the Ministry of Land, Infrastructure, Transport and Tourism’s guidelines for construction result management, the results can be used with confidence as official survey outputs.

Furthermore, using AR functions you can visualize positions from design drawings on site, or guide staking and reference points with on-screen guides. With LRTK, staking tasks that previously required multiple people can be performed efficiently by one person. The UI is designed to be intuitive so that even those without specialized surveying skills can operate it, making site introduction easy without high training costs. LRTK, which embodies “smartphone-only + centimeter accuracy (half-inch accuracy),” can be said to be a new proposal that will serve as a trump card for promoting DX at future surveying sites. By utilizing such solutions, surveying operations will become more familiar and efficient. As a step to further advance on-site DX, consider introducing LRTK.

FAQ

Q: What is RTK surveying? A: RTK surveying is a surveying method that uses two receivers—a base station (a receiver placed at a known point) and a rover (a receiver at the measurement location)—to obtain high-precision positions in real time by correcting positioning errors. By applying differential corrections to GPS errors, coordinates can be obtained with centimeter-level accuracy.

Q: What is GNSS? A: GNSS stands for Global Navigation Satellite System, a collective term for satellite positioning systems operated by various countries, such as GPS (U.S.), GLONASS (Russia), Galileo (EU), and BeiDou (China). Combining signals from multiple GNSS satellites improves positioning accuracy and stability. In RTK surveying, using signals from the whole GNSS rather than GPS alone allows acquisition of more satellite data and contributes to higher accuracy.

Q: What level of accuracy can RTK surveying achieve? A: When operated properly, RTK surveying can generally achieve horizontal accuracy of about 2–3 cm (0.8–1.2 in) and vertical accuracy on the order of several centimeters (several in). However, accuracy varies with satellite reception conditions and distance from the base station. Better conditions yield more stable centimeter-level accuracy.

Q: Can RTK surveying be done with only a smartphone? A: Yes. With compatible high-precision GNSS receivers and correction information services, RTK surveying can be performed with a smartphone. Recent smartphones have high-performance GNSS capabilities, and combining them with external GNSS units can achieve positioning comparable to traditional surveying instruments. By using a dedicated app to receive correction information (such as network reference station data), centimeter accuracy surveying is possible on a smartphone even without dedicated equipment.

Q: What are the benefits of using the cloud? A: The biggest benefit of using the cloud is the ability to immediately share and store data obtained on site. Uploading survey results to the cloud on the spot and sharing them with office staff enables rapid instructions for re-measurement and data verification. Also, by obtaining correction information via the cloud as with network RTK, you can eliminate the need to set up a base station each time. Centralized online data management and analysis improve the overall efficiency and accuracy of surveying.

Q: What is LRTK? A: LRTK is a solution for performing centimeter-accuracy surveying and 3D scanning using a smartphone. It consists of a compact high-precision GNSS receiver (the LRTK device) that attaches to a smartphone, a dedicated app, and cloud services. By combining these components, even a single person can easily perform high-precision surveying. Its hallmark is that surveying can be completed centered on the smartphone without the need for bulky traditional equipment.