Improving On-site Efficiency with GNSS Terminals: Time Savings from Centimeter-level Positioning

In construction and surveying sites, efficiency and productivity improvement are major challenges. In recent years, the promotion of smart construction (i-Construction) using ICT has begun to introduce digital technologies into on-site surveying work. At the same time, modern construction management increasingly demands accurate finishes according to drawings, requiring positioning accuracy of a few centimeters or less (a few in or less) in more situations. Conventional GPS (GNSS) positioning can produce errors of about 3-10 m (9.8-32.8 ft), making it inadequate for applications that require high precision. Among the emerging solutions, high-precision positioning at the centimeter level achieved by GNSS terminals (centimeter-level positioning (cm level accuracy (half-inch accuracy))) has attracted particular attention. This new technology, which achieves significant work time reduction and labor savings compared to traditional surveying methods, is explained here in terms of the effects it brings to on-site efficiency.

Traditional surveying work and time challenges

Traditional surveying required skilled techniques and multiple personnel. Optical surveying instruments such as total stations and levels were commonly used, and work was typically done in pairs. One person operated the instrument while the other stood at a remote point holding a prism or staff to define the target point. Survey instruments also needed to be carefully mounted on tripods and leveled and adjusted for height, which took time to set up and dismantle. When measuring a large site, the instrument had to be repositioned repeatedly to gradually expand the measurement area, and it was not uncommon for surveying a single site to take several days.

In addition, traditional workflows involved an analog step of recording data on paper field books on-site and organizing and drafting drawings back at the office. Even when electronic data could be extracted from instruments, coordinate system transformations and CAD input often had to be performed, making it difficult to share and utilize data in real time. Moreover, maintaining high precision required regular calibration and maintenance of instruments. When instruments were sent to the manufacturer for adjustment, they became unusable and there was a risk of work stopping during that time.

Thus, conventional surveying was time-consuming and labor-intensive, and because it relied on specialized technicians it was difficult to reduce personnel. It became necessary to review the traditional approach that consumed large amounts of manpower and time and shift to more efficient methods.

Emergence of GNSS terminals and centimeter-level positioning

As a trump card to solve these issues, GNSS surveying using satellite positioning systems has emerged. GNSS (Global Navigation Satellite System) is a general term for multiple satellite positioning constellations such as GPS (United States), Russia’s GLONASS, Europe’s Galileo, and Japan’s Quasi-Zenith Satellite System (QZSS “Michibiki”). GNSS receivers (antennas) receive radio signals from multiple satellites overhead and calculate their position as coordinates on Earth from the differences in signal arrival times.

The advantage of satellite positioning is that it can directly obtain “world coordinates” over a wide area without requiring line-of-sight on the ground. Unlike total stations, which measure relative distances from reference points, positioning can be performed instantly at remote points as long as communication with satellites is maintained. This makes it possible to handle situations that were previously time-consuming—such as surveying in poor-visibility terrain, remote locations, or wide-area layout—more efficiently.

However, to use GNSS effectively for surveying, a major improvement in positioning accuracy was essential. Standalone positioning typically has errors of about 5-10 m (16.4-32.8 ft), which is far from the accuracy needed for surveying. That led to the development of a high-precision positioning technique known as RTK (Real Time Kinematic). RTK performs simultaneous GNSS observations at a base station with a known position and at a rover, and the base station transmits error information to the rover in real time, allowing correction of errors and achieving centimeter-level high-precision positioning. It is, so to speak, a method of “measuring with two units simultaneously to cancel errors,” neutralizing the error factors inherent in GPS.

In Japan, since the 2000s, the practical use of RTK positioning has expanded alongside the establishment of the Geospatial Information Authority’s continuous GNSS observation network (electronic reference points). Recently, network RTK—where correction information can be received nationwide via the Internet—and QZSS “Michibiki”’s centimeter-level augmentation service (CLAS) have appeared, enabling high-precision positioning without preparing one’s own base station. As a result, GNSS-based surveying is becoming common in civil and land surveying and is attracting attention as a labor-saving technology that enables surveying to be completed by a single person. High-precision GNSS receivers are beginning to penetrate the field as a new choice of surveying equipment alongside total stations, and they are poised to significantly change surveying styles.

Efficiency benefits of introducing GNSS terminals

Introducing high-precision GNSS terminals on-site brings a variety of efficiency benefits not available with traditional methods. The main points are summarized below.

• Easy operation through smartphone integration: Modern GNSS terminals can be used in conjunction with smartphones or tablets, eliminating the need for dedicated controllers. They can be operated intuitively on familiar smartphone screens, making them easier to handle even for people without specialized surveying skills. Positioning and data saving can be started with one touch from an app, and a variety of functions—such as automatic coordinate system conversion and distance/area calculations between measured points—are integrated. Being able to survey with a smartphone-like interface without worrying about complex equipment operation leads to significant time savings.

• Centimeter-level positioning with RTK: RTK technology can reduce positioning errors to within a few centimeters. Where ordinary GPS might be off by several meters, RTK-enabled GNSS terminals can determine positions with horizontal accuracy of several centimeters and vertical accuracy of several centimeters (several in). With this high precision guaranteed, reliably trustworthy positioning results can be obtained immediately in situations that previously required repeated careful re-measurements. Because confirmations of as-built conditions and stakeout positions can be determined accurately in a single attempt, rework is reduced and the overall speed of operations increases. RTK positioning can obtain a high-precision fixed solution (Fix) in just several tens of seconds, so workers are not left waiting long periods for each point measurement.

• Intuitive stakeout with AR guidance: Combining GNSS terminals and smartphones enables visual guidance using AR (augmented reality) technology. The smartphone camera view can overlay target points or lines from design drawings onto the site footage, showing workers the direction to move and installation positions with arrows or markers. This eliminates the traditional labor of measuring with a tape while looking at drawings, and even less-experienced technicians can be intuitively guided to accurate points. AR-based stakeout also helps prevent work errors and makes coordination between surveying and construction smoother.

• Immediate data sharing via cloud synchronization: Positioning data recorded with a GNSS terminal can be uploaded to the cloud from a smartphone on-site. Data can be shared within the company immediately after measurement, allowing instant verification and utilization on office PCs. Remote personnel can check measurement data instantly, reducing information transmission loss between the site and office. There is no need to record data in paper field notebooks and bring them back, eliminating time lags caused by delayed data transfer. For example, reflecting measurements in drawings or starting quantity calculations can begin the same day surveying is completed, enabling subsequent design and construction processes to start earlier. Real-time sharing speeds up decision-making, directly improving overall project efficiency.

• 3D records using point clouds: The fusion of high-precision GNSS and digital technologies has made it easy to record sites in 3D. By integrating smartphone camera imaging or LiDAR scanners, high-precision 3D point cloud data can be acquired simply by photographing the site. Because GNSS position information is attached to the acquired point cloud, a high-dimensional, dimensionally accurate 3D model of the current state can be preserved similar to photogrammetry or laser scanner outputs. Space data acquisition, which previously required specialized equipment, can now be completed with just a GNSS terminal and a smartphone, further advancing and simplifying site record-keeping and as-built management. In addition, advanced data utilization—such as automatic earthwork volume calculation from acquired 3D data or verifying as-built against design models—is now possible.

• Labor reduction (one-person surveying): By introducing GNSS terminals, surveying work can be completed by a single person. As noted earlier, total stations typically required two people, but with GNSS surveying a single worker can walk to desired points holding the antenna and sequentially acquire coordinates (dramatically increasing the number of points that can be observed in a day). Work previously outsourced to external surveyors can be handled in-house if the company equips its staff with GNSS gear, reducing outsourcing costs and scheduling hassles. There is no need to wait for a surveyor to arrive if personnel are unavailable, enabling immediate measurements when needed. The reduction in personnel and work time directly leads to cost savings, offering significant managerial benefits. In an industry chronically short of labor, the productivity improvements from labor reduction are especially significant.

• High mobility to rapidly cover wide areas: GNSS receivers have become very compact in recent years, dramatically improving portability. Pocket-sized GNSS terminals have appeared, eliminating the need to carry heavy tripods or large equipment. Because line-of-sight conditions are not required for positioning, simply walking with the antenna across a large site allows efficient acquisition of measurement points to every corner. Without time lost to repositioning equipment, the daily coverage area expands greatly. Built-in batteries enable long-hour operation, reducing the risk of interrupting daytime work due to battery depletion and allowing nimble surveying. Robust designs with dust and water resistance allow equipment to be carried in rainy or dusty conditions without worry.

• Improved safety: Increased work efficiency also improves safety. Shorter work times and less time spent on site reduce risks such as heatstroke in hot, humid environments and accidents in high places or on roads. Surveying around heavy machinery or in high-traffic areas can be completed more quickly. Because equipment can be operated solo and is lightweight, the physical burden of carrying heavy gear is lessened, helping prevent falls and drops. Simplifying complex procedures reduces human error, which in turn helps prevent accidents and rework. The combination of efficiency gains and improved safety is a major advantage of introducing the latest GNSS terminals.

Promoting smart surveying solutions with LRTK

Finally, as a concrete example of high-precision GNSS terminals, we introduce the LRTK series. The LRTK series is a compact, lightweight GNSS positioning terminal that integrates antenna, receiver, power, and communication modules in one, featuring an all-in-one design that pairs with smartphones via Bluetooth. It has dust- and water-resistant performance for reliable use in harsh outdoor civil engineering and construction environments. Among them, the LRTK Phone is a groundbreaking RTK receiver that fits in the palm of the hand (weight approximately 160 g; thickness about 1 cm (0.4 in)) and can be attached to commercial smartphones such as the iPhone via a dedicated case. With this single device, centimeter-level positioning can be achieved anytime, anywhere without preparing a large base station or controller. In addition to corrections via RTK networks, it supports CLAS augmentation signals provided by Japan’s QZSS “Michibiki,” so high-precision positioning is not interrupted even in mountainous areas outside cellular coverage. It also supports multi-GNSS reception of multiple constellations such as GPS, GLONASS, and Galileo, and multiple frequencies such as L1/L2, enabling stable high-precision positioning even in environments with many obstructions or unfavorable satellite geometry. In real measurements it secures accuracy of about ±2 cm (±0.8 in) horizontally and ±4 cm (±1.6 in) vertically, providing precision comparable to conventional large surveying equipment in an easy-to-use form.

LRTK works with a smartphone app to perform everything from starting positioning to recording points and even stakeout navigation via intuitive on-screen operations. When mounted on a dedicated pole, automatic height correction is performed, allowing a single staff member to complete full-scale surveying. In addition to high-precision coordinate measurement with a complete LRTK system, it enables 3D scanning using a smartphone’s LiDAR or camera, on-site projection of design models with AR, and automatic recording of position and orientation on photos. Tasks that previously required separate equipment and processes can now be handled by a single device, dramatically simplifying the workflow from data acquisition to utilization.

With the advent of LRTK, the notion that “surveying is a special task for experts only” is being overturned. Site personnel can now perform measurements themselves as needed, eliminating time lost waiting for surveyors or outsourcing. Some advanced construction firms and municipalities have already introduced LRTK on their sites and begun using high-precision positioning in daily operations. For example, at one construction site, a construction manager was able to perform as-built verification with LRTK without waiting for a surveyor, significantly reducing idle time. The LRTK series is a smart surveying tool that achieves both work time reduction and productivity improvement in construction, civil engineering, and surveying. It is also a cutting-edge solution compatible with the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction initiative (site ICT), strongly supporting the next generation of on-site operations. Consider adopting the high-precision GNSS terminal LRTK as a simple surveying solution to further accelerate on-site efficiency and DX (digital transformation). In an industry where labor shortages are becoming more serious, the use of such high-precision technologies can be said to hold the key to the future of site management.