RTK-GNSS Comparison: Cloud Sharing Changes the Construction Site! The As-Built Management Revolution Brought by LRTK

Table of contents

• What is RTK-GNSS surveying? Comparison with traditional methods

• How cloud sharing transforms the field: Utilizing real-time surveying data

• As-built management revolution: Dramatic efficiency gains brought by LRTK

• Comparison points between conventional RTK surveying and LRTK

• Summary: The evolution of RTK-GNSS and the new era opened by LRTK

• FAQ

What is **RTK-GNSS surveying**? Comparison with traditional methods

On construction sites there is growing interest in RTK-GNSS surveying, which can measure positions with millimeter-level accuracy (mm; in). RTK (Real Time Kinematic) is a technology that corrects GNSS satellite positioning errors in real time to enable centimeter-level high-precision positioning (cm; in). Standalone GPS positioning has errors on the order of several meters (m; ft), but with the RTK method those errors can be reduced to just a few centimeters (cm; in). This improvement in accuracy has made it possible to use GPS for tasks that were previously difficult, such as as-built (post-construction shape) verification and precise layout/positioning work.

In RTK, two GNSS receivers are typically used: a reference station (base station) installed at a known coordinate, and a mobile station (rover) that determines position while moving. The reference station continuously sends the error information it measures to the mobile station, which applies corrections to its position measurements to improve accuracy. The key point is obtaining the "FIX solution" that resolves the integer ambiguity in the phase differences of the satellite signals. Once this FIX solution is resolved, RTK can achieve true centimeter-level accuracy (half-inch accuracy). However, with conventional RTK surveying, installing the reference station and performing the initial setup took time and effort, and it was common to require two or more people.

Comparison with conventional surveying methods: Until relatively recently, optical surveying instruments such as total stations and levels—which used to be mainstream—required multiple workers and considerable time to achieve precise measurements. Conventional GNSS surveying also lacked sufficient real-time accuracy, requiring post-processing at the office after measurements. In contrast, RTK-GNSS surveying is revolutionary in that it can obtain high-precision positions on the spot without prior establishment of control points or complex calculations. In particular, recent advances in satellite positioning technology and communications infrastructure have made it possible to receive RTK correction information without field-deployed base stations. For example, in Japan there are services that distribute correction data from the Geospatial Information Authority of Japan’s electronic reference point network, and systems are being put in place to receive centimeter-level augmentation signals (half-inch accuracy) from quasi-zenith satellites. By leveraging these, RTK positioning becomes possible without preparing additional base stations, lowering the barrier for small sites and for cases introducing RTK for the first time. These technological advances, together with the government’s *i-Construction* push, mean that field surveying is entering a turning point toward digitalization.

How Cloud Sharing Is Changing the Site: Leveraging Real-Time Survey Data

Along with advances in RTK-GNSS technology, cloud-connected data sharing is transforming on-site work efficiency. Traditionally, survey results were first compiled onto paper drawings or notes and then taken back to the office for data processing and reporting. Photo records likewise required combining digital camera images with handwritten notes and later marking the photo locations on drawings. Now, by using smartphone apps and the cloud, it is possible to record and share data on the spot as measurements are taken.

For example, with the latest smartphone-compatible RTK surveying devices, because they can take photos and input notes simultaneously with positioning, you can instantly record on-site a set of information consisting of location coordinates + photos + notes. Because each survey point can automatically package "what was measured where", there is no need to later match photos with measurement values. Furthermore, with a single tap to upload data to the cloud, information collected on-site can be instantly shared over the Internet. Office staff and clients can also view the latest measurement results and site photos in real time, dramatically speeding up reporting and communication.

Using a dedicated cloud-based viewer, you can visualize uploaded positioning points and trajectories on a map and review captured photos and acquired 3D point cloud data together with project stakeholders. There is no longer any need to carry paper drawings or photo albums, and it becomes easy to grasp site conditions remotely. By sharing surveying data in the cloud, the time lag of "measure on site → organize in the office" becomes zero, enabling on-the-spot confirmation of as-built conditions and construction decisions. Indeed, the surveying workflow is being renewed by digitization, and one could say that on-site DX (digital transformation) is progressing.

Revolution in As-Built Management: Dramatic Efficiency Gains Brought by LRTK

In public works and the civil and construction sectors, as-built management, the process of verifying that completed structures conform to design drawings, is a critical process. Traditionally, this as-built verification has been carried out through manual measurements using tape measures and leveling staffs, along with photographic documentation. Personnel measure thickness, height, width, and so on point by point at various locations on the structure, and compare the values against the specification values on the drawings. The measurement results are compiled into an "as-built management table" and submitted together with construction photographs. However, the traditional manual methods centered on handwork have many issues, and the main problems are as follows.

• High manpower and time burden: Conducting on-site measurements requires deploying many personnel and spending long hours, and administrative work to compile the results into drawings and tables also arises, creating a significant burden. It is also necessary to arrange skilled surveying technicians, and under labor shortages it can be difficult to proceed efficiently within the project schedule.

• Risk of overlooking due to limited measurement points: Manual measurement has a physical limit to the number of points that can be measured, making it difficult to cover the entire as-built condition. With limited measurement points, small discrepancies with the design drawings can be missed, and there was a risk of being told at inspection that it was "different from the drawings" and scrambling to correct it.

• Human error such as missing records: On busy sites, mistakes like forgetting to take photos or recording measurement values incorrectly tend to occur. For example, if photos are not taken before backfilling buried items, there will be no evidence after completion, which in the worst case can lead to rework or disputes.

Because of the issues described above, conventional as-built management methods had limitations in both efficiency and accuracy. Against this backdrop, a new technology, LRTK, which combines RTK-GNSS and smartphones, has emerged and is revolutionizing as-built management on construction sites.

LRTK is a system that mounts a pocket-sized GNSS receiver to a smartphone or tablet, designed so that anyone can easily carry out centimeter-level surveying (cm level accuracy, half-inch accuracy). By attaching a device weighing approximately a little over 100 g and simply launching the dedicated app, high-precision positioning can begin, with no complicated initial setup required. RTK surveying, which traditionally required time for tripod installation and adjustments between devices, can with LRTK achieve positioning almost immediately after powering on, allowing work to start on site without waiting. The RTK-specific FIX solution can also be obtained rapidly using a proprietary algorithm, making measurements at each survey point smooth.

Another attractive feature is their ease of adoption. LRTK terminals are priced lower than conventional surveying instruments, making it realistic for sites to provide "one device per person". In fact, on advanced construction sites, not only surveying specialists but each worker carries an LRTK, establishing a system that enables immediate precision surveying when needed. Their ease of use and usefulness are highly valued on site.

Furthermore, LRTK is characterized by its all-in-one versatility in a single unit. Not only does it measure position coordinates, it can also utilize a smartphone’s camera and sensors to scan wide areas and acquire high-density 3D point cloud data. The acquired point clouds and photo data are automatically saved to the cloud on site, allowing them to be shared with the office the moment measurements are finished. For example, in road construction, using LRTK enables rapid completion of as-built measurements of the roadbed and pavement, so all stakeholders can review the results within the same day. Surveying and recording work that previously took half a day has been greatly streamlined, leading to prevention of measurement omissions and rapid corrective action. Also, by using the LRTK app’s AR feature to overlay reference lines and target elevations from the design drawings onto live site footage, tasks that traditionally required two people—such as batter-board setup (establishing reference points) and height checks—can be performed accurately by one person.

LRTK also contributes to safety. In situations such as steep slope work, where surveyors traditionally had to enter slopes despite the danger, LRTK can complete the task simply by scanning point clouds from a distance. Because it can record the terrain’s 3D shape in detail without contact, it can ensure worker safety while also achieving precise capture of the finished shape. Even on expansive development sites, because it can automatically measure many points while walking to create a ground surface model, it can capture the finished surface and even the volumes of fill and cut (work quantities). As a result, the ability to complete wide-area finished-shape management and quantity verification with the minimum necessary personnel can be considered revolutionary.

Data obtained with LRTK can be used in a form that also complies with the Ministry of Land, Infrastructure, Transport and Tourism's construction quality management guidelines. For example, if absolute coordinates are assigned to LRTK point cloud data using known control points, the measurement results can be submitted as official construction quality inspection materials. Even today, as electronic delivery and the use of three-dimensional data advance, with LRTK you can use data acquired in the field directly to create official documents and CAD drawings. In other words, LRTK has not only made on-site surveying work accessible to anyone, but also provides results at a level that can be used for inspection and delivery as before. It is regarded as a solution that strongly promotes the DX (digitalization) of construction quality management, in that it enables quality control work to be carried out efficiently and reliably without relying on expensive specialized equipment or large numbers of skilled workers.

Comparison points between conventional RTK surveying and LRTK

Conventional RTK-GNSS surveying (conventional method) and LRTK, a new smartphone surveying system, differ in many ways. Below are the main comparison points.

• Required equipment: In the conventional method, multiple devices such as a GNSS receiver for the base station, a GNSS receiver for the rover, a communication modem, and a dedicated controller were required. With LRTK, surveying can be completed with a smartphone and a palm-sized GNSS receiver.

• Initial setup: With the conventional method, it took time to establish reference points on site and configure the equipment. LRTK does not require a base station; attach the unit to your smartphone and turn it on to start positioning immediately.

• Number of personnel: The conventional method typically required two or more people (to operate the surveying instrument and assist). With LRTK, one person can handle positioning and recording.

• Measurement range: The conventional method measured points one by one, making it laborious to cover large areas. LRTK can record the site in planar and three-dimensional detail using point-cloud scanning, reducing oversights.

• Data recording: The conventional method required taking photos with a separate camera and keeping notes. LRTK can capture photos and notes simultaneously with positioning, and photos are automatically linked to coordinates.

• Data sharing: With the conventional method, data were organized and shared after returning to the office. LRTK can share results immediately from the field via the cloud, allowing real-time progress monitoring.

• Safety: The conventional method carried risks when surveying hazardous areas such as steep slopes. LRTK enables non-contact measurements from a safe distance, allowing the as-built condition of dangerous areas to be verified safely.

• Implementation cost: The conventional method required an expensive set of surveying equipment. LRTK uses low-cost units and existing smartphones, reducing initial investment and making it easy to deploy multiple devices for use across an entire site.

Summary: The evolution of RTK-GNSS and the new era opened by LRTK

RTK-GNSS surveying technology has advanced dramatically in recent years, and integration with the cloud and mobile devices has transformed field operations. Positioning and as-built measurements that were traditionally left entirely to specialized surveying teams can now be performed with smart tools that anyone on site can use. At the forefront of this is LRTK, an all-in-one platform that integrates high-precision positioning, data recording, and cloud sharing, and is being adopted at many construction sites.

Moreover, even in the construction industry—where chronic labor shortages and calls for work-style reform are growing louder—the importance of introducing labor-saving and advanced tools like LRTK to job sites will only increase. By leveraging LRTK, surveying tasks that were traditionally complex can be handled simply as simplified surveying, and results can be shared immediately. The ability to easily implement high-precision as-built management makes it possible to achieve both quality assurance and productivity improvement. With LRTK leading a new era of RTK-GNSS, the way sites operate will become even smarter going forward. Please consider adopting the latest technology at your site and experience its benefits for yourself.

FAQ

Q: What is RTK-GNSS? How does it differ from conventional GPS? A: RTK-GNSS is a positioning technology that achieves centimeter-level high accuracy by correcting satellite positioning errors in real time. Ordinary GPS (standalone positioning) has errors of several meters, but RTK can reduce those errors to a few centimeters by using correction information from a reference station. For that reason, it is used in applications that require high accuracy, such as land surveying and as-built management.

Q: Is a base station always required to perform RTK surveying? A: Traditionally, it was common to install a base station (a GNSS receiver that serves as the reference point) on site. However, in recent years, by using network RTK services provided by national or private entities and augmentation signals from satellites, RTK positioning has become possible without a dedicated base station. For example, LRTK can utilize these correction information, allowing you to begin centimeter-level positioning without deploying additional equipment.

Q: Can LRTK be operated without surveying expertise? A: Yes. LRTK is designed with an intuitive smartphone app and a simple equipment configuration, making it easy to use even without professional surveying skills. The app presents clear guides and menus, allowing one-touch execution from starting positioning to saving and sharing data. Unlike traditional surveying instruments, users do not need to perform complex settings or calculations.

Q: Can data obtained with LRTK be used for official as-built management? A: Of course. Point cloud data and coordinate information measured with LRTK can be utilized in accordance with existing as-built management procedures. For example, if measurement data are corrected to an accurate coordinate system using reference points, they can be used as-is to produce deliverables submitted for as-built inspections of public works. They also support electronic delivery data and are recognized as surveying and measurement methods that meet the i-Construction standards promoted by the Ministry of Land, Infrastructure, Transport and Tourism.

Q: Compared to conventional total-station surveying, what advantages does LRTK offer? A: Total stations require line of sight to a prism and may need to be re‑set up at each location or operated by two people. In contrast, LRTK uses satellite positioning, so it is easier to obtain positions even in areas with poor visibility, and basically a single person can measure each point in the field by operating a handheld smartphone. There is also a difference in the amount of data that can be acquired at once. LRTK with smartphone measurements can capture many points and photos in a short time and immediately record them digitally. On the other hand, total stations excel at precise point‑by‑point measurements, so using each method where appropriate can further improve the efficiency and accuracy of field surveying. Note that in tunnels or indoors where GNSS signals do not reach, total stations remain necessary, so it is important to use them in combination according to site conditions.

Q: Can LRTK be used at sites without radio or communications coverage? A: Yes. LRTK supports not only network-based corrections but also satellite augmentation signals that can be used even outside communication coverage. Even in mountainous areas without cellular service, if you receive correction information from quasi-zenith satellites overhead, high-accuracy positioning is possible. In other words, even where there is no internet connection, RTK surveying with LRTK can continue as long as there is a clear view of the sky. The flexibility to choose the optimal correction method according to site conditions is also a strength of LRTK.