Cloud-Connected × Centimeter-Level Accuracy! Transforming Construction Sites with Smartphone-Only RTK Surveying

Table of Contents

• What is RTK surveying?

• Why centimeter-level accuracy is required on construction sites

• Challenges of traditional surveying methods

• The emergence of smartphone-only RTK surveying

• Further efficiency through cloud integration

• How RTK surveying transforms construction sites

• What is simplified surveying with LRTK?

• FAQ

In recent years, a new surveying method that combines smartphones with high-precision positioning technology has been attracting attention in the construction industry. Conventional GPS typically produces errors on the order of several meters (several ft), but by using a method called RTK surveying, it has become possible to measure positions with centimeter-level accuracy. Moreover, because positioning data can now be shared and managed in the cloud, on-site operational efficiency is improving dramatically.

Pocket-sized RTK-GNSS receivers that attach to smartphones have also appeared, ushering in an era when anyone can easily perform precise surveying. In construction sites facing labor shortages and a decline in experienced surveyors, the combination of cloud integration and centimeter-level accuracy could be the key to a productivity revolution. This article explains the basics of RTK surveying, how it differs from traditional methods, the benefits of smartphone-only surveying and cloud usage, and concludes with an introduction to simplified surveying solutions using LRTK.

What is RTK surveying?

First, let’s briefly look at how RTK surveying (real-time kinematic surveying) works. Standard GPS found in smartphones and car navigation systems typically has position errors on the order of several meters (several ft). These errors accumulate due to various factors such as signal delay while passing through the atmosphere, satellite clock errors, and multipath reflections from buildings. With RTK positioning, these errors are canceled out by simultaneously observing satellite signals at two points: a base station (a receiver installed at a known location) and a rover (the receiver at the point to be measured). By comparing the data received by both receivers in real time and removing common error factors, highly accurate positions can be calculated.

In RTK, correction data is sequentially sent from the base station to the rover, and the rover applies real-time corrections to its position. Network-based RTK using wireless or internet communication (such as Ntrip or VRS) is also common, and correction information can be received from fixed base-station networks (such as the Geospatial Information Authority of Japan’s continuously operating reference stations). With this mechanism, RTK surveying can achieve centimeter-level accuracy that standalone positioning cannot. In good conditions, horizontal errors are typically around 2–3 cm (0.8–1.2 in) and vertical errors around 3–4 cm (1.2–1.6 in), providing an order-of-magnitude improvement over conventional GPS positioning (errors of several meters (several ft)).

Why centimeter-level accuracy is required on construction sites

On construction and civil engineering sites, positional shifts of several meters (several ft) are unacceptable. High accuracy is always required for surveying to construct structures at the correct location and elevation. Centimeter-level positioning can have major impacts on the following on-site tasks:

• Establishing reference points and layout marking: When setting out reference points and marking pile-driving locations for buildings and structures, even slight deviations are unacceptable. RTK surveying can instantly determine coordinates on-site that match the drawings, allowing accurate layout marking.

• As-built management and quality inspection: High-precision positioning is essential to verify that constructed elements conform to design drawings. Measurements that traditionally required levels or total stations and considerable time can be done quickly at many points with RTK-GNSS, detecting deviations down to a few centimeters.

• Earthwork volume calculations and excavation depth management: High-precision surveying helps calculate the volume of cut and fill and confirm whether excavation has reached the required depth. Reduced errors enable more accurate material estimates and less waste in construction planning.

• Infrastructure inspection and displacement measurement: For maintenance of roads and bridges, it is necessary to periodically measure surface subsidence and structural displacement to track changes over time. While leveling surveys were traditionally required to detect centimeter-level changes, RTK makes it possible to remotely capture equivalent accuracy in a short time.

Challenges of traditional surveying methods

High-precision surveying has historically depended on specialized surveyors. Total station surveying requires skill for setting up and operating the equipment and typically works in teams of two. With an aging workforce and fewer young technicians, such person-dependent methods are reaching their limits in on-site responsiveness. Project schedules can be affected by surveyor availability, and there can be long delays from request to deliverables, highlighting efficiency issues under labor shortages.

Traditional high-precision GNSS surveying systems (RTK systems) also involved many portable items—full base-station setups, rovers, radios, large batteries—making equipment transport to sites a challenge. Initial costs tended to be high, creating a barrier for small contractors. Survey records were often handwritten or manually entered, requiring later digitization and introducing risk of errors.

Against this backdrop, the construction industry is accelerating its DX (digital transformation) initiatives. Under the *i-Construction* movement promoted by the Ministry of Land, Infrastructure, Transport and Tourism, efficiency using ICT and 3D data is being advanced. Adoption of new technologies such as drone photogrammetry, 3D laser scanning, and machine guidance is progressing, and there is high expectation for compact surveying devices that “anyone can use.” Technological advances have made high-precision positioning more affordable and accessible than before, and on-site surveying practices are entering a transition period.

The emergence of smartphone-only RTK surveying

Smartphone-only RTK surveying devices that overturn conventional wisdom have been developed. For example, a pocket-sized RTK-GNSS receiver that attaches to an iPhone or iPad can achieve centimeter-level positioning with just that one device. The main unit weighs only about a hundred-odd grams, with a thickness of around 1 cm (0.4 in), making it extremely compact and lightweight; the antenna, GNSS receiver, battery, and communication module are integrated. There is no longer a need to connect devices with cables as before; wireless pairing with the smartphone greatly improves on-site handling.

On the smartphone side, measurements are performed using a dedicated app. Current positioning accuracy and coordinates are displayed in real time on the screen, and tapping a button records coordinates for any chosen point. Time and satellite tracking status are automatically recorded with the measurement, and point names or notes can be entered on-site. Because acquired coordinates are converted on the spot to Japan Geodetic System plane coordinates and elevations, cumbersome calculations and handwritten field books are unnecessary. It truly feels like your smartphone becomes both the surveying instrument and the field book, allowing on-site staff without specialized knowledge to operate it intuitively. A single person can carry the equipment and complete surveying, reducing personnel coordination burdens.

Moreover, the latest compact RTK receivers have made significant technical advances. They use GNSS chips supporting multiple frequencies, making them less susceptible to building reflections and ionospheric errors that plagued earlier systems, and making it easier to obtain a robust fixed solution. Some models support the centimeter-level augmentation service (CLAS) provided by Japan’s quasi-zenith satellite system “Michibiki,” enabling high-precision positioning in mountainous or remote island sites using augmentation signals from satellites alone. Such improvements are making it increasingly realistic for RTK surveying to be used “anytime, anywhere, by anyone.” Device prices have also fallen considerably compared to the past, and in the future it may become normal for each on-site staff member to have one surveying device.

Further efficiency through cloud integration

Smartphone-only surveying is also groundbreaking because acquired data can be saved and shared directly to the cloud. If coordinates and point-cloud data measured on-site are uploaded to the cloud with a single tap from the smartphone, office staff can instantly review the results. For example, in as-built inspections, measurement data can be shared immediately via the cloud so inspectors located remotely can grasp the situation in real time. There is no longer the hassle of sending data by USB or email after surveying; information coordination between field and office becomes seamless.

The cloud also offers functions to make surveying data more useful. Uploaded survey points are plotted on maps, and distances, areas, and volumes between any two points can be measured from a web browser. Without installing dedicated software, all stakeholders can access, analyze, and review the latest survey results, speeding up report creation and consensus building. Sharing a generated view-only URL lets clients and subcontractors check data without logging in, smoothing external information sharing.

Cloud integration dramatically improves management of surveying results. Paper records and manual entry errors decline, and centralized data management improves reliability. Real-time communication between site and office reduces rework and accelerates decision-making. The system in which survey data is put to use on the cloud the moment it is collected on-site is precisely what will drive DX in the construction industry.

How RTK surveying transforms construction sites

As introduced above, the fusion of centimeter-accuracy RTK surveying with smartphones and the cloud brings major transformations to construction sites. Let’s summarize the main benefits again.

• Labor savings (addressing labor shortages): With just a smartphone and a small survey device, a single person can perform surveying, reducing the number of team members previously required. Even without experienced surveyors on site, construction managers can perform surveying themselves, making it easier to sustain operations amid personnel shortages.

• Efficiency (speed-up): Real-time data sharing and analysis during surveying dramatically increase overall work speed. Processes that previously waited for survey results to be incorporated into drawings can now synchronize site and office information in real time, reducing rework and shortening project durations.

• Improved safety: There are fewer occasions to carry heavy tripods and instruments into hazardous zones, reducing worker burden and improving safety. Quick point measurements shorten time spent working on roads. AR features allow pile-driving positions to be viewed and guided from a distance, minimizing work in dangerous locations such as heights or road shoulders.

• Improved accuracy and quality: Consistently acquiring high-precision survey data raises the level of construction quality control. Installation positions and elevations of critical structures can be accurately verified, aiding early error detection and reducing rework. Continual data acquisition for as-built checks advances both quality assurance and process visualization.

• Digital information sharing: Because on-site survey information is immediately stored as digital data, omissions and transcription errors are prevented. With the same data shared and viewable on the cloud by the entire team, communication among site, design, and clients becomes smoother. Accumulated data can be used for project reviews and feedback for future projects.

What is simplified surveying with LRTK?

Finally, as a concrete solution that embodies the technologies discussed so far, we introduce LRTK. LRTK (LRTK) is a compact RTK-GNSS system that achieves centimeter-level positioning using a smartphone. Among them, the “LRTK Phone” is an all-in-one surveying device integrated with a smartphone; the receiver body is lightweight at approximately 125 g and small enough to fit in a pocket. Simply attach the receiver—whose antenna and power supply are built in—to an iPhone/iPad with a dedicated case, and you can conduct high-precision surveying anytime, anywhere.

LRTK, working in concert with a smartphone app, enables intuitive simplified surveying that anyone can operate. From the app, you can check positioning status and record/manage points with a single button, and it includes features such as automatic coordinate conversion, automatic point naming, and attaching photos and notes. Acquired data can be uploaded directly to the LRTK cloud, where stakeholders can share and analyze it through a browser-based 3D viewer. Integration with the smartphone camera and AR functions allows advanced construction support such as projecting drawing positions onto the real scene for pile-driving. LRTK combines accuracy and functions comparable to traditional large surveying equipment with markedly greater ease of use.

Thus, LRTK embodies the “democratization of surveying,” enabling high-precision on-site measurements even by non-experts. It contributes to significant reductions in work time and productivity improvements and aligns with the *i-Construction* initiatives promoted by the Ministry of Land, Infrastructure, Transport and Tourism. By leveraging LRTK’s smartphone-only, cloud-connected RTK surveying, new on-site operations that overturn conventional practices can be realized. If you are considering labor-saving and advanced surveying for construction site operations, why not try simplified surveying with LRTK?

FAQ

Q: What is RTK surveying? A: RTK surveying is a method that uses two GNSS receivers—the base station and the rover—and compares their observation data in real time to correct errors, enabling centimeter-level high-precision position measurements. While conventional GPS positioning has errors of several meters (several ft), RTK surveying substantially cancels those errors using correction information from the base station, allowing current position determination within a few centimeters.

Q: What is required to perform RTK surveying? A: RTK surveying requires an RTK-capable high-precision GNSS receiver (rover) and a base station that provides correction data. The base station can be set up by the user, but it is common today to receive correction information (such as Ntrip) over the internet from national or commercial continuously operating reference station networks. A controller to process and record data received by the rover (a dedicated terminal, tablet, smartphone, etc.) is also needed. Recently, the combination of smartphones and small receivers has made it easy to perform the entire RTK surveying workflow.

Q: Can you really survey with just a smartphone? A: Standalone smartphone GPS has errors of several meters (several ft) and is therefore difficult to use directly for precision surveying. However, if you use an external RTK-GNSS receiver that attaches to the smartphone together with a dedicated app, the smartphone can be used as a high-precision surveying device. The small receiver acquires high-precision satellite positioning data, while the smartphone handles correction calculations and data management, enabling surveying accuracy and functionality comparable to conventional dedicated equipment.

Q: What are the benefits of cloud integration? A: By linking surveying data to the cloud, information sharing between site and office becomes much smoother. If coordinates and point clouds obtained on-site are uploaded instantly, remote team members can check results in real time. Data stored centrally in the cloud eliminates USB handovers and manual entry, reducing the risk of errors. Cloud tools also allow distance, area, and volume calculations and comparison with drawings, making data usable without special software.

Q: What kind of product is LRTK? A: LRTK is the name of a high-precision GNSS surveying system designed to be used with a smartphone. It consists of a small RTK-GNSS receiver that can be attached to a smartphone (such as LRTK Phone), a dedicated app, and cloud services, aiming to make centimeter-level surveying easily accessible to anyone. It brings the accuracy and functions of traditional surveying equipment into a compact device and dramatically improves on-site surveying efficiency.