Table of Contents

• Existing Condition Survey

• As-built Measurement

• Setting Out (Layout Marking)

• Pile Driving Guidance

• Boundary Survey

• Volume Calculation

• Photo Documentation (Construction Photos)

• Simple Surveying with LRTK

• FAQ

Introduction

Surveying and various measurement tasks at construction sites require significant time and manpower. From existing condition surveys to as-built inspections, setting out and guiding pile driving, and even confirming property boundaries, calculating earthwork volumes, and taking construction record photos, this series of indispensable processes has traditionally involved a lot of labor. In recent years, however, the construction industry has accelerated DX (digital transformation), and with initiatives such as i-Construction, ICT technologies have begun to be applied to on-site surveying and construction processes. Among these, RTK (Real-Time Kinematic) positioning is attracting attention as a technology that dramatically improves surveying efficiency (shortening work time and reducing labor) and surveying accuracy.

RTK is a high-precision satellite positioning technique that uses a base station and a rover to correct GNSS satellite signal errors in real time, enabling immediate acquisition of position coordinates with errors on the order of a few centimeters. Traditional surveying using total stations or levels required line-of-sight between survey points and multiple people to perform the tasks, but RTK positioning uses absolute coordinates from satellites so a single person can perform layout and measurements. Also, the setup of control points can be simplified by using network RTK, greatly reducing preparation time.

So, how much can work time actually be reduced by introducing RTK? One demonstration reported that ICT construction (including RTK surveying and drone use) reduced the average duration for road construction initial surveys from 17.7 days to 2.7 days, about a 70% reduction. If surveying processes are made that efficient, it directly shortens overall schedules and reduces labor costs.

This article estimates the efficiency gains RTK brings to various surveying and construction processes. For key tasks—existing condition surveys, as-built measurements, setting out (layout marking), pile driving guidance, boundary surveying, earthwork (volume) calculation, and photo documentation—we consider how much work time can be reduced by utilizing RTK and explore possibilities for business improvement. At the end, we also introduce a simple surveying solution using smartphones called LRTK.

Existing Condition Survey: Efficiency Gains from RTK

First, let's look at efficiency gains in existing condition surveys (topographic surveys) before construction begins. Traditionally, a two-person team with a total station tripod and another person holding the prism measured points one by one. On sites of several hectares, the number of survey points is large, and repositioning equipment and ensuring line-of-sight take time, often occupying a full day.

With RTK positioning, this changes dramatically. After setting up a base station (or using network RTK), a worker can walk around with a rover receiver and rapidly observe terrain points one after another. For example, for a topographic survey of around 50 points, tasks that traditionally took two people about half a day have been reported to be completed by one person in just a few hours with RTK. Of course, results vary depending on the site's GNSS reception environment and satellite availability, but under favorable conditions, the time required for an existing condition survey can be shortened to a fraction of the original time. This not only greatly reduces the required surveying time but also means tasks that previously required multiple personnel can be handled by one person, reducing labor costs and scheduling burdens.

Also, because RTK positioning acquires coordinates in real time, data can be shared to the cloud on site and decisions to take additional measurements can be made immediately if points are missing. This prevents “re-deployment due to forgotten measurements,” further improving overall operational efficiency.

As-built Measurement: Speeding Up As-built Control

Next, the effect of RTK on as-built measurement (as-built surveying) after construction. As-built control—verifying that finished works such as road subgrade elevations and installed structural elements match design dimensions—is essential for quality assurance. Traditionally, survey teams entered the site at stage breaks, measured heights and positions using batter boards and levels, and recorded results, making inspections time-consuming. For example, to check embankment heights, survey staff picked up points at set intervals and later produced drawings and difference calculations in the office.

With RTK, as-built inspections are also greatly streamlined. Construction staff themselves can use RTK receivers mounted to smartphones to measure key elevations and coordinates immediately after work and check differences from design values on the spot, so inspections that used to take half a day can be completed in a very short time and remedial decisions made immediately. Point recording is automated, reducing forgotten measurements and recording errors and eliminating rework. Furthermore, RTK's centimeter-level positioning (half-inch accuracy) reduces human error, minimizing measurement variability due to operator skill. Since consistent accuracy is obtained regardless of who measures, site supervisors and foremen can check as-built conditions on their own, allowing progression to the next stage without waiting for specialist surveyors. RTK positioning that balances quality control and efficiency thus offers large time savings and reduces rework in as-built management.

Setting Out (Layout Marking): Reducing Labor in Layout Work

RTK is also powerful for setting out (layout marking), the work of establishing the positions of structures. Traditionally, dimensions were derived from drawings, reference lines and elevation benchmarks were established on site, and multiple workers drove wooden stakes and strung lines to indicate the building outline. On cramped sites or roadworks, this staking is labor-intensive and often requires repeated measurements to ensure accuracy.

With RTK, layout marking can be greatly reduced in labor. By loading design data into a dedicated app on a smartphone fitted with an RTK receiver, construction management personnel can walk the site alone and mark positions corresponding to design coordinates. It is also conceivable for heavy equipment operators to confirm pile centers themselves using high-precision GNSS, and cases where layout work that used to take 2–3 people half a day or more can be completed by one person in a short time are entirely possible. With fewer people on site, coordination with operating heavy machinery becomes easier, and hazardous tasks at openings or heights can be reduced. Setting out using RTK not only shortens work time but also contributes to improved safety as an efficiency measure.

Pile Driving Guidance: Improving Heavy Equipment Positioning Efficiency

RTK has a significant effect on guiding pile driving for foundations of bridges and buildings. Traditionally, surveyors visited the site, marked the intersection positions from drawings on the ground, and instructed heavy equipment operators. To prevent pile misplacement, heavy equipment was often stopped and positions checked repeatedly, making guidance for a single pile time-consuming.

After RTK introduction, these pile center-setting procedures are greatly simplified. Using a smartphone or tablet with a GNSS receiver, design pile center coordinates can be confirmed on site immediately, enabling workers to mark correct locations and guide the pile driver themselves. Combined with AR (augmented reality), design positions can be overlaid on the smartphone screen for guidance. This greatly reduces the time required to check and correct pile positions and decreases waiting time for heavy equipment. Accurately placing piles from the first attempt reduces the risk of schedule delays due to rework. RTK-based pile driving guidance improves both construction accuracy and operational speed.

Boundary Survey: Shortening Time for On-site Meetings

RTK is also effective for boundary surveys conducted for public projects, land acquisition, and determining boundaries with neighboring landowners. For boundary confirmation involving meetings with adjacent landowners and government offices, it is desirable to complete on-site surveying as smoothly as possible. Traditionally, temporary benchmarks were established on site based on coordinates of known points, then total stations were used to measure angles and distances to determine boundary stake positions. Multiple re-measurements and calculations were required to finally set boundary points, so stakeholders often had to be present for extended periods.

With RTK surveying, once reference coordinates are established, simply holding a receiver over each boundary point and pressing a button records coordinates, allowing multiple boundary points to be measured in a short time. For layout tasks, entering the pre-calculated boundary point coordinates into the device and using a navigation function to guide to the point enables one person to accurately restore boundary markers. Even in forests or hilly terrain where line-of-sight cannot be ensured, as long as satellite signals are receivable each point can be measured individually, eliminating the need to clear sightlines as in traditional methods. RTK boundary surveys therefore shorten the time required for meetings and reduce burdens on both officials and attendees.

Moreover, because survey point data are electronically recorded and saved to the cloud on site, tasks like coordinate calculations and drawing preparation are automated. As a result, the efficiency of the entire boundary determination workflow, up to producing documents for government submission, improves dramatically.

Volume Calculation: Accelerating Earthwork Computation with Point Cloud Measurement

Calculating volumes of embankment and excavation is also greatly streamlined by RTK. In earthworks, periodic measurement of remaining spoil or backfill volumes is necessary for progress management and planning haulage. Traditionally, survey teams measured cross sections at set intervals on site and performed volume calculations back in the office. Creating cross-sectional drawings and performing numerical computations took time, creating a lag before results were available and delaying progress understanding.

With RTK, combined with drone photogrammetry or 3D scanning, high-density point cloud data can be obtained quickly and volumes can be calculated immediately. For example, by integrating a smartphone-mounted LiDAR (laser scanner) with RTK positioning, walking while scanning the surroundings can generate a 3D model of the current conditions. The obtained point cloud data is automatically analyzed in the cloud, and embankment and excavation volumes are immediately available. Volume calculations that used to take half a day or more can now be completed the same day, allowing measurement frequency to be increased and enabling daily visibility of construction progress.

Using drones equipped with RTK-GNSS also enables aerial survey with minimal ground control points (GCPs) even over wide areas, making earthwork management for large-scale reclamation sites more efficient. RTK accelerates volume calculation and greatly shortens the PDCA cycle of earthwork management.

Photo Documentation (Construction Photos): Streamlining Data Management

RTK-driven digitization also benefits the task of taking and managing construction record photos. Photographs taken before and after construction and photos documenting key stages need to be taken in large numbers and organized in ledgers for each process, and this organization consumes unexpected amounts of time. Traditionally, after taking photos with a camera, locations and orientations were noted manually, photos were pasted into ledgers in the office, and captions were added.

Current solutions using RTK automatically add location (geotag) and orientation information to photos and allow management by mapping photos to maps or drawings. For example, photos taken with a smartphone or 360° camera are instantly plotted on a cloud map, eliminating the need to later search for “which point a photo corresponds to.” If integrated with photo ledger creation software, positioning data automatically records shooting angles and locations and organizes them, reducing the need for site supervisors to work late into the night organizing photos. By letting on-site staff focus on photographing and leaving data organization to digital systems, the time spent on photo documentation can be drastically reduced. Additionally, the high-precision location information provided by RTK reduces discrepancies when matching photos with future drawings or point clouds, improving the reliability of construction records.

Simple Surveying with LRTK: High-Precision Positioning with a Smartphone

Finally, we introduce LRTK, a solution attracting attention for easily applying these RTK technologies on site. LRTK (Light RTK) is a surveying system consisting of an ultra-compact RTK-GNSS receiver that can be attached to a smartphone and a dedicated app, turning a handheld smartphone into a high-precision surveying device. A major feature is that without preparing dedicated heavy equipment, a smartphone alone can handle control point surveying, as-built checks, and layout marking. For example, by attaching an LRTK device to a smartphone and receiving network RTK correction information, you can start centimeter-level surveying (half-inch accuracy) as soon as you arrive on site. Complex equipment operation and cable connections are unnecessary, and the intuitive usability allows anyone to operate it. Furthermore, models that support QZSS (Michibiki) CLAS augmentation signals can maintain high-precision positioning even in areas without mobile communications, enabling stable high-precision surveying in mountainous areas where surveying was previously difficult.

The benefits of LRTK go beyond mere miniaturization. By combining smartphone cameras and AR (augmented reality) functions, surveying and construction management become more intuitive. Using RTK-derived self-positioning as a reference, design lines and structural models on drawings can be overlaid on the real world, so you can see at a glance “what is to be placed here” through the screen. Even without complex drawing interpretation or traditional setting out, simply pointing the smartphone allows accurate position confirmation, enabling less experienced workers to locate positions without error. Smartphone RTK solutions like LRTK open high-precision positioning to more on-site staff and realize “simple surveying” that can be performed by fewer people.

To fully realize the time-saving effects described above, tools must be easy for anyone to use. In this respect, the LRTK series is a state-of-the-art solution compatible with i-Construction promoted by the Ministry of Land, Infrastructure, Transport and Tourism and could become a trump card for on-site DX from surveying to construction management. If you are considering RTK for labor-saving and efficiency improvements, consider adopting LRTK for smart surveying.

FAQ

Q: How accurate is RTK positioning? Is it comparable to a total station? A: Generally, RTK-GNSS can achieve approximately 1–3 cm (0.4–1.2 in) horizontal accuracy and about 3 cm (1.2 in) vertical accuracy in open environments. It does not reach the millimeter-level strictness of optical total stations in all cases, but for many civil engineering surveys and construction management tasks it provides sufficient accuracy. Considering benefits such as measuring wide areas at once and the fact that global positioning does not accumulate errors between control points, RTK is practically comparable. However, accuracy can degrade due to multipath (signal reflection) or blockage when tall buildings or trees surround the site, so it is advisable to choose locations with good sky visibility when performing RTK surveys.

Q: Do you need special skills or qualifications to use RTK surveying? Can one person handle it? A: RTK surveying itself does not require special national qualifications. With a basic understanding of device operation and positioning principles, it can be used even by non-surveyors. Unlike traditional total station work, there is no need for an assistant to hold a prism, and in principle one-person operation is possible. Positioning apps on site provide guidance, so advanced skills such as instrument leveling or angle reading are not required. However, judging the accuracy of obtained coordinates and reflecting survey results in drawings requires some knowledge of surveying standards and coordinate systems. Also, for official survey deliverables, it is still advisable to perform work under the supervision of a licensed surveyor.

Q: Can RTK surveying be done at sites without network connectivity, such as mountainous areas? A: Yes. Network RTK correction information is typically delivered via mobile networks, but in areas without mobile coverage there is an option to use the QZSS (Michibiki) “CLAS” augmentation signals. CLAS-compatible RTK receivers can receive correction information from satellites and maintain centimeter-level positioning (half-inch accuracy) even in mobile network dead zones. However, in dense forests where sky visibility itself is poor, satellite signals may not be received and RTK solutions may fail to obtain a fixed solution. In such cases, measures such as temporarily surveying from an open location and transferring relative positions, or combining with traditional methods, may be necessary.

Q: Introducing RTK seems costly—does it offer good cost-effectiveness? A: Introducing RTK requires initial investments in receivers and possibly correction service subscriptions, but the efficiency gains often make it cost-effective. For example, if a survey that previously required two people a full day can be completed by one person in a few hours, labor cost savings can be substantial. Recently, low-cost smartphone-compatible RTK receivers and monthly subscription correction services have become available, so high-precision positioning is attainable without the hundreds-of-thousands-of-dollars investments of the past. Considering productivity improvements and labor savings on site, RTK typically provides very high cost-effectiveness.

Q: If we have RTK, can we stop using total stations and levels altogether? A: RTK streamlines many surveying tasks, but traditional instruments still have roles in certain situations. For example, in tunnels or building interiors where satellite signals cannot reach, total stations and levels remain indispensable. Also, for short-distance leveling requiring millimeter precision or equipment alignment measurements, optical instruments can be more reliable. Therefore, rather than replacing all traditional instruments with RTK, it is recommended to use RTK for outdoor wide-area surveys and complement it with optical instruments for fine, detailed measurements. Using both appropriately will balance productivity and accuracy across surveying tasks.