Precision position guidance with GNSS terminals! Anyone can perform accurate layout marking

Layout marking, an indispensable task at construction and surveying sites, is a critical process that affects a project’s quality and progress. However, this positioning task has traditionally required skilled interpretation of drawings and a great deal of manpower and time, imposing a burden on sites. What is attracting attention now is precision position guidance using GNSS terminals. By combining satellite positioning technology with the latest digital technologies, an era is arriving in which anyone can easily perform accurate layout marking.

This article first organizes the traditional challenges of layout marking and explains the use of GNSS terminals as a solution. It then examines in detail the benefits that the latest technologies bring to the field, such as centimeter-level positioning with RTK, easy operability through smartphone integration, intuitive guidance with AR (augmented reality), and data sharing via the cloud. At the end of the article, we introduce a simple surveying tool called “LRTK” that embodies these technologies and propose a new layout-marking method that is easy for anyone to adopt.

Challenges of traditional layout marking

Layout marking is the process of accurately transferring positions and lines from drawings to the field in architectural and civil engineering work. Traditionally, this work has been carried out using ink lines (墨つぼ), chalk, tape measures, and surveying instruments such as laser layout devices and total stations. For example, to set out the positions of building walls or the axes of equipment, you measure dimensions based on reference axes or string lines and mark the floor or ground. Accurate positioning requires knowledge and experience in interpreting drawings, and even minor measurement mistakes can lead to later construction errors, so this process has required skilled craftsmanship.

Layout marking is required across all stages from foundation work to finishing and equipment installation, so its accuracy and efficiency are directly linked to the overall quality and schedule of the project.

However, traditional layout marking has several challenges. First is the burden of manpower and time. Surveying and layout marking are usually performed by teams of two or more, with one person operating the surveying equipment and another doing the marking. There is also the hassle of setting up and moving large, heavy equipment, and it is not uncommon for marking many points across a wide site to take a full day. Because layout marking is required at every stage, a tremendous amount of work time is spent across the whole project.

Second is dependence on skilled workers. Layout marking demands advanced drawing-reading ability and measurement skills, so sites tend to rely on specific veteran workers. If that person is absent, other work can halt while waiting for layout marking. In recent years, the aging of craftsmen and a shortage of younger workers have made securing personnel with skilled layout-marking ability a problem.

There are also issues of accuracy control and safety. Manual layout marking cannot avoid the risk of dimensional errors or positional shifts due to human error. Especially for setting out foundations or pile-driving, millimeter-level accuracy is required, but there are limits to what manual positioning can achieve. When marking in areas where heavy machinery is operating, attention must also be paid to worker safety.

As such, traditional layout marking has required great effort and skilled technique, creating problems on sites in terms of efficiency and personnel. In response, a new layout-marking method using GNSS terminals is attracting attention as a way to solve these problems.

Centimeter-level high accuracy with RTK positioning

A GNSS terminal is a device that receives signals from satellite positioning systems, including GPS, to determine its position. Smartphones also have GPS functionality, but standalone positioning typically yields accuracy on the order of meters, which is insufficient for construction site layout marking. By using RTK (real-time kinematic) positioning, however, errors can be reduced to within a few centimeters (a few in).

With RTK positioning, correction data is received from a reference station (base station) installed at the site or from reference information via the Internet, and applied in real time to the positioning results of the GNSS terminal, which acts as the rover. This mechanism cancels out slight shifts and error factors in satellite signals, enabling accuracy of about horizontal ±1–2 cm (±0.4–0.8 in) and vertical accuracy on the order of a few centimeters (a few in). Precision positioning that used to require expensive surveying equipment has become possible recently with small GNSS receivers and an Internet connection.

In Japan, infrastructure supporting RTK, such as the Geospatial Information Authority’s electronic reference point network and the quasi-zenith satellite system “Michibiki,” provides centimeter-level augmentation services (CLAS). This makes it possible, even at mountain sites or locations out of normal communication coverage, for compatible GNSS terminals to obtain high-precision correction information directly from satellites.

If RTK-compatible GNSS terminals are used for layout marking, coordinate values written in design drawings (for example, building grid intersection points) can be specified directly as targets at the site. Because the device continuously positions itself to centimeter accuracy and calculates the relative distance to the specified coordinates, it can guide directly to the designed positions. There is no longer a need to follow distances from reference lines with a tape measure or to repeatedly re-measure positions. Global coordinates obtained from GNSS satellites directly link site and drawing location information, preventing cumulative errors between points. Precision positioning via RTK underpins the digitization and high-accuracy realization of layout marking.

A surveying tool anyone can use through smartphone integration

Many GNSS terminals can be used in conjunction with smartphones or tablets. By installing a dedicated app on a smartphone and attaching a small GNSS receiver, an everyday device can instantly become a high-accuracy surveying instrument. In the past, dedicated survey controllers and complicated initial setups were required, but now you can start/stop positioning and save data by tapping buttons on the smartphone screen. Because it can be operated intuitively without special expertise, it can be said to be a surveying tool that anyone can use.

The advantages of smartphone integration go beyond operability. You can leverage the rich functions of smartphones to greatly improve convenience. For example, you can digitally record date/time, point names, and notes simultaneously with positioning, or take photos and associate them with location data in the app. The need to write in paper field books disappears, and all data is stored electronically on the smartphone. Measured coordinates can be automatically converted on the spot to plane rectangular coordinate systems or elevations (geoid heights), allowing immediate confirmation of practical values at the site. This allows field technicians themselves to casually perform small measurements and checks without waiting for the surveying staff, increasing the number of cases where decisions can be made on site.

Furthermore, integrating the smartphone with the GNSS terminal achieves portability not found in traditional large surveying equipment. Carrying a compact device that fits in a pocket and can be taken out and used when needed lightens field work. The ability to perform “opportunistic surveying” makes it possible to handle small layout and measurement tasks on the spot that were previously postponed, improving on-site productivity.

Intuitive position guidance using AR technology

Combining GNSS terminals with smartphone apps enables position guidance using AR (augmented reality) technology. AR overlays digital information onto camera images from a smartphone or tablet; familiar examples include games like Pokémon GO and AR navigation features in map apps. On construction sites, AR can be used to visually indicate instructions such as “mark here.” If target points and reference line data from design drawings are loaded into the app, the points and lines can be overlaid on the real scene on the smartphone screen. Workers can understand at a glance where to mark simply by looking at the screen. Because there is no need to mentally match drawings and the actual site, even less experienced workers can accurately identify positions without hesitation.

AR guidance can be described as a car navigation system for construction sites. Workers can walk around the site with a smartphone, and arrows or guide displays on the screen lead them to the target position. As they approach the target, the remaining distance is displayed as “X cm to go,” and when the target point is reached, a marker on the screen aligns perfectly. In some cases, planned wall lines or equipment piping routes are projected onto the ground in AR, enabling marking along virtual lines. These visual feedbacks allow accurate layout marking to be performed by anyone without relying on veterans’ intuition or experience.

Dramatic labor reduction and operational efficiency gains

Layout marking with GNSS terminals greatly contributes to labor reduction on site. Tasks that used to require teams of two can be completed by one person, substantially reducing personnel. In the construction industry, which is facing serious labor shortages, the ability for a limited number of workers to accomplish more tasks is highly valuable. In fact, even at sites without a resident surveying specialist, if field technicians themselves can perform positioning with a GNSS terminal, the waste of work delays caused by “waiting for surveying” can be eliminated. As a result, work schedules run more smoothly, shortening overall construction periods and reducing labor costs.

At the same time, introducing the latest technologies dramatically improves on-site operational efficiency. Immediate positioning with RTK-GNSS and AR guidance shorten layout-marking time itself, and fewer measurement mistakes mean fewer rework cycles. Automatic recording and sharing of data reduce the need to manually plot measured values on drawings or compile reports. Because site-collected information is shared with the office via the cloud immediately, downstream decision-making becomes quicker. These effects raise overall on-site productivity and quality, enabling high performance even with fewer personnel. Such labor reduction and digital efficiency gains align with the Ministry of Land, Infrastructure, Transport and Tourism’s push for i-Construction and construction DX, and will become increasingly important.

Real-time data sharing with cloud utilization

GNSS terminals and smartphone apps also integrate with cloud services, making data sharing between the field and the office markedly easier. Positioning data, photos, and notes collected at the site can be uploaded to the cloud with a single tap from the app. Measured points and their information are instantly plotted on cloud maps, allowing office staff to grasp the latest situation in real time. This eliminates the previous hassle of taking measured values back to the office to update drawings and share them by email. Because information is synchronized with remote stakeholders at all times, communication loss is reduced and decision-making speeds up.

It is also easy to share data with external stakeholders via the cloud. Certain survey data can be published as web-accessible shared links, facilitating smooth information transfer to clients and subcontractors.

Accumulating data in the cloud enables unified information management. For example, coordinate lists and drawing data created at the design stage can be imported into GNSS terminals via the cloud for field work, or coordinates of marked positions measured in the field can be saved to the cloud as construction records. All surveying and layout-marking data remain digitally, making it easy to verify measured values later or review construction outcomes. Cloud utilization connects the field and the office and ties past and present data, further improving the accuracy and efficiency of construction management.

Easy simple surveying with LRTK

As a concrete example of solutions that leverage RTK positioning, smartphones, AR, and the cloud, a GNSS terminal called “LRTK” has attracted attention in recent years. LRTK is a system composed of an ultra-compact RTK-GNSS receiver and a smartphone app. By attaching this receiver to a smartphone, a palm-sized device instantly becomes a versatile surveying instrument with centimeter-level accuracy (a few in). The unit weighs only a few hundred grams and is lightweight and compact for easy carrying on site. Nevertheless, it achieves surveying-grade high accuracy with RTK precision positioning, and acquired data is automatically synced to the cloud. It also features coordinate navigation functions for layout marking and AR guidance, allowing even beginners to reach target points without hesitation.

LRTK’s uses extend beyond coordinate measurement and layout marking to include surrounding 3D point cloud measurement using the smartphone camera or LiDAR, and on-site composite display of design models using AR. Capable of calculating distances, areas, and volumes with a single device, it is truly an all-purpose surveying tool that covers most on-site digital measurement needs.

The key feature of LRTK is that it is an easy-to-use simple surveying tool for anyone. It is relatively inexpensive as a dedicated device and easy to introduce; with just a smartphone, one device per person can be brought to the site and used. Because it can be operated intuitively without advanced training, site staff can perform measurements and layout marking when needed without relying on a surveying department. As a result, the labor reduction and efficiency benefits described above can be enjoyed immediately. LRTK is a device that accelerates on-site DX and transforms layout marking into a task anyone can perform. When incorporating high-accuracy simple surveying into your site in the future, please consider introducing such cutting-edge tools. You will likely experience a speedy and accurate work process that overturns conventional wisdom.

The labor savings and quality improvements achieved through precision position guidance can be seen as a productivity revolution for sites. Smart layout marking using GNSS terminals is sure to become the new norm at future construction sites. Why not update your layout-marking practices with new technologies and give GNSS terminals a try on your site? Experience the effects firsthand. With precision position guidance, open up the future of your site.