Table of Contents

• Background: Why earthwork volume calculations and point cloud data utilization are gaining attention

• The importance of positioning technology that determines point cloud accuracy

• What is RTK? Basic knowledge and types of receivers

• Why RTK receivers are effective for earthwork volume calculations and as-built management

• Characteristics of RTK receivers that are easy to introduce (compactness, smartphone integration, all-in-one, etc.)

• Case studies of on-site implementation (labor reduction, same-day deliverables, accuracy improvements, etc.)

• Implementation steps and selection points (price information excluded)

• Practical workflow for obtaining point cloud control points via smartphone surveying using LRTK

• On-site use cases (stake setting, photogrammetry, AR navigation, volume calculation)

• Conclusion: Outlook for efficiency and high-precision management using RTK receivers

• FAQ: Frequently asked questions about RTK receivers, positioning accuracy, and point cloud data integration

Background: Why earthwork volume calculations and point cloud data utilization are gaining attention

In recent years, on construction and surveying sites, earthwork volume calculations and the use of 3D point cloud data have been attracting significant attention. This trend is driven by the spread of ICT technologies promoted by initiatives such as the Ministry of Land, Infrastructure, Transport and Tourism’s "i-Construction" and the need to improve productivity in response to a shortage of experienced workers. Traditionally, progress management and earthwork volume calculations required cross-section surveys on site and manual calculations, consuming a great deal of time and effort. However, with the advent of drone photogrammetry and 3D laser scanners, terrain can now be recorded in detail as point cloud data, and volumes can be calculated digitally. In addition, using LiDAR scanners built into smartphones and tablets makes it easy for anyone to perform 3D scans on site. As a result, precisely capturing terrain changes before and after construction and using them for earthwork volume calculations and as-built (final shape) verification is becoming the new norm.

Point cloud utilization is especially a game changer for earthwork volume calculations. Previously, the common method was to measure heights at fixed intervals to create cross-sections and calculate volumes using the average cross-section method. This approach required a lot of work and carried the risk of overlooking some local terrain changes. By contrast, using point clouds derived from drone photos or laser scanners allows the ground surface to be recorded thoroughly and the volume to be accurately calculated from those differences. Once point cloud data has been obtained, recalculations for other areas are easy without additional surveying. In practice, a major construction company reported that earthwork measurement and calculation work that had taken four people seven days was reduced to two people one day by switching to drone imaging and point cloud processing. The accuracy of volume calculations from point clouds has also been confirmed on site to be comparable to traditional methods (about 1% error). Thus, introducing point cloud data greatly reduces work time and manpower while enabling sufficient accuracy to grasp as-built quantities, which is why its importance continues to rise.

The importance of positioning technology that determines point cloud accuracy

For accurate use of point cloud data, positioning technology during surveying is extremely important. No matter how dense a point cloud is, if it is not placed in the correct coordinate system for the site, comparisons with design drawings or volume calculations will produce errors. For example, drone photogrammetry can generate high-precision point clouds from captured images, but if the location information (geotags) attached to each point is inaccurate, the precision required for as-built management cannot be guaranteed. For this reason, it has traditionally been necessary to perform "georeferencing" (coordinate alignment) by establishing control points via GNSS surveying and aligning point cloud data to those references.

Positioning information provided by standard smartphones or GPS devices is generally accurate only to several meters, making them unsuitable for precise civil engineering surveying. On the other hand, among satellite positioning technologies, the RTK method (Real-Time Kinematic) can obtain position coordinates with errors in the order of a few centimeters. In other words, by assigning position information to point clouds via RTK positioning, the entire point cloud dataset can be placed into a high-precision coordinate system. This enables advanced digital construction management such as accurately detecting discrepancies between design 3D data and point clouds for as-built management, or strictly comparing multiple survey datasets over time to monitor increases and decreases in earthwork volumes. Combining point cloud data with high-precision positioning technologies like RTK is indispensable to fully exploit point cloud accuracy, and its importance has been increasingly recognized in recent years.

What is RTK? Basic knowledge and types of receivers

RTK (Real-Time Kinematic) is a positioning technology that uses signals from GNSS satellites, including GPS, to correct positioning errors in real time and achieve centimeter-level accuracy. The basic mechanism involves a reference station (base station) placed at a known position and a mobile station (rover) receiving satellite signals simultaneously; the error information calculated at the reference station is sent to the rover, enabling high-precision relative positioning. Standalone GPS positioning can suffer meter-level offsets due to atmospheric effects and satellite orbit errors, but RTK corrects these to reduce errors to within a few centimeters.

There are several types of RTK receivers. Traditionally, systems combining a stationary high-performance antenna and a dedicated controller, used in base station/rover sets, were mainstream. Recently, however, network RTK services that use correction information over the Internet from networks such as the Geospatial Information Authority of Japan’s reference station network and private correction services have become widespread, allowing positioning with just a single rover receiver in many cases. Technological advances have also led to miniaturization and cost reductions of receivers, and portable or smartphone-integrated RTK receivers have emerged. Where large stationary antennas and UHF radios were once required, there are now products that perform RTK positioning simply by attaching a palm-sized antenna to a smartphone. Receiver types range from high-precision dual-frequency models to cost-saving L1 single-frequency units; selecting the right one depends on on-site usability and the required accuracy.

In Japan, a method to obtain correction signals is also provided by the nation’s quasi-zenith satellite system "Michibiki" through the Centimeter-Level Augmentation Service (CLAS). An RTK receiver that supports CLAS can perform RTK positioning via signals from the Michibiki satellites even in mountainous areas where Internet connectivity is difficult. As such, environments where positioning is possible without setting up your own base station are becoming more common, significantly lowering the barrier to RTK adoption compared to the past.

Why RTK receivers are effective for earthwork volume calculations and as-built management

Introducing RTK receivers dramatically improves the efficiency and accuracy of earthwork volume calculations and as-built management in civil engineering. There are several reasons for this.

First, improved measurement accuracy. RTK enables centimeter-level positioning that was impossible with conventional handheld GPS, allowing point cloud and survey point data to be recorded with high reliability. For example, if ground levels before and after excavation or embankment are measured with RTK, the volume derived from those differences becomes highly accurate. Volumes that were previously approximated with cross-sections can be directly calculated from high-density point clouds obtained via RTK, yielding results with minimal discrepancies during on-site verification.

Next, improved work efficiency. With an RTK receiver, a single worker can survey many points in a short time. Traditionally, as-built management often required two or more people using a level or total station. RTK-GNSS enables single-person operation over wide areas without allocating assistants or note-takers. Because positioning results are available in real time, ground elevation and structure positions can be checked on the spot and discrepancies with the design immediately identified. This allows checks such as whether all embankments have reached design elevation or whether the roadbed as-built shape is within tolerance to be done the same day, and if necessary, immediate instructions for additional fills or trimming can be issued.

Furthermore, digital data integration is a major strength. Point data obtained with an RTK receiver are recorded in a unified coordinate system including plane coordinates and elevations, so they can be directly imported into CAD drawings or CIM models. Multiple days’ survey data can be compared against the same reference, enabling quantity-based progress management or creation of as-built heat maps for quality assessment. Recent combinations of RTK positioning with tablets allow point cloud data captured on site to be shared with the office via the cloud instantly, so all stakeholders can make decisions based on the same up-to-date data. The introduction of RTK receivers thus speeds up the entire process from surveying to analysis and sharing, not only ensuring measurement quality but also serving as a key driver for on-site digital transformation (DX).

Characteristics of RTK receivers that are easy to introduce (compactness, smartphone integration, all-in-one, etc.)

Modern RTK receivers incorporate many features designed to make on-site adoption easier. Below are the particularly noteworthy characteristics.

• Compact and lightweight design: Recent RTK receivers are very compact; some fit in a pocket. With body weights around 100 g and models offering dust and water resistance, they are easy to carry and robust enough for field use. There is no longer a need to carry large fixed antennas or heavy batteries, significantly reducing the physical burden on workers.

• Smartphone integration: More RTK receivers connect to smartphones or tablets via Bluetooth or cables and are operated through dedicated apps. This eliminates the need for expensive dedicated controllers; the familiar smartphone screen can complete positioning tasks. With a simple tap of a "Start Positioning" button, coordinates are captured and plotted on a map within the app, providing an intuitive UI that is easy for beginners. Using the smartphone’s communication capabilities to connect to correction services over the Internet (e.g., Ntrip) also allows users to start RTK positioning without complex setup.

• All-in-one functionality: All-in-one refers to systems that handle everything from positioning to data management. Modern RTK receivers and compatible apps can automatically convert captured coordinate data into designated coordinate systems (e.g., a specific plane rectangular coordinate zone) and elevation systems (such as geoid height) and record them. They also let you assign names and notes to each survey point or attach photos for unified on-site information management. Integration with cloud services allows field data to be uploaded to servers immediately for internal sharing. Such all-in-one workflows remove post-survey data organization and transcription errors, shortening the time from surveying to reporting.

• Easy setup: To lower the adoption barrier, RTK receivers have become simpler to set up on site. Examples include models with built-in batteries that run for long periods without power cables, quick-release mounts that attach to smartphones with one touch, and attachments that substitute a monopod for a bubble level or height-measuring staff. These features shorten the time from arrival on site to the start of positioning and enable anyone to begin surveying quickly.

Latest RTK receivers with these features (for example, smartphone-integrated "LRTK" series) are attracting attention from field practitioners as “easy-to-adopt, easy-to-use RTK.” Because no special skills are required, high-precision positioning can now be used in everyday tasks by personnel other than surveying specialists.

Case studies of on-site implementation (labor reduction, same-day deliverables, accuracy improvements, etc.)

Sites that have introduced RTK receivers report a variety of benefits. Here are representative cases and effects.

• Labor reduction and improved safety: At a municipal disaster recovery site, a smartphone-connected RTK receiver was used to survey a collapsed slope. A single worker was able to measure the unstable, hard-to-access slope from a safe distance and acquire the needed point cloud data. Work that previously required a multi-person survey team was completed by one person, and reducing entry into hazardous areas improved safety. At another site, reducing manpower for control point surveying allowed concurrent work on other tasks, shortening the overall construction schedule.

• Same-day deliverables: In a case combining drone photogrammetry and RTK receivers, aerial images shot in the morning were processed into point clouds and volumes by the afternoon, allowing same-day reporting to the site manager. Because RTK provided accurate coordinates, there was no need for additional position adjustments on the generated point cloud model, enabling quick volume computations. Having deliverables the same day made timely on-site decisions possible; for example, if excavation was found to be short by a certain number of cubic meters, orders to increase work the next day could be issued promptly, facilitating schedule adjustments.

• Improved accuracy and quality assurance: In road construction as-built management using RTK, verification accuracy for paving thickness and roadbed elevations improved. By comparing point cloud data with design 3D models and producing a color-coded heat map of elevation differences across the finished surface, localized areas of insufficient thickness that had been overlooked were identified. This capability is possible only with the high-precision alignment that RTK provides, allowing immediate on-site remediation to meet quality standards. Thus, RTK receiver use has been valued not only for shortening survey time but also for raising construction quality through more reliable measurement data.

• Data sharing and remote supervision: A construction company used RTK receivers and the cloud to implement real-time sharing of survey data. When field staff uploaded as-built point clouds captured with a tablet and RTK receiver to the cloud, managers and clients at the office could view the data almost immediately. This enabled partial implementation of remote construction supervision, where as-built conditions could be checked and instructions given without a site visit. For managers overseeing multiple remote sites, the ability to reduce travel time while accurately monitoring each site is a significant advantage, and broader adoption is expected.

Implementation steps and selection points (price information excluded)

When introducing RTK receivers on site, be sure to follow these steps for smooth utilization and keep the following points in mind when selecting devices or services.

• Clarify the introduction purpose: First, organize what you want to improve with RTK receivers. Is it efficiency in earthwork volume calculations, improved accuracy in as-built measurements, or use for machine guidance or stake setting? Required functions and accuracy differ by purpose. Once the purpose is clear, required positioning accuracy (e.g., planar position ±2 cm, elevation ±5 cm) and equipment configuration (single rover or base station + rover) for the survey area become apparent.

• Check the operating environment: Next, confirm the environment of the site. If a mobile data signal is available, using a network RTK (Ntrip service) is convenient. In areas with poor communications, such as mountain regions or underground sites, you will need to set up your own base station or choose a receiver that supports Michibiki’s CLAS signals. Also consider the work area size and presence of obstacles. GNSS signal reception can be unstable in high-rise urban areas or forests, so using other surveying equipment in combination may be necessary.

• Select equipment: Compare RTK receivers suitable for your purpose and environment. Key points are positioning accuracy and reliability (multi-GNSS support, dual-frequency support, tilt/attitude correction availability, etc.), usability (smartphone compatibility, Japanese-language support, intuitive UI), durability (IP ratings, shock resistance), and battery life (can it last a full day). In actual field use, water resistance for light rain, heat-resistant designs for prolonged use in sun, and verified operation in cold climates are important criteria. While price ranges vary, choose a model that fits your operations rather than simply going by budget.

• Training and trials: After purchasing (or renting) the equipment, conduct internal training and trials before full deployment. Use manufacturer or dealer training sessions and online manuals to learn basic procedures such as starting/stopping positioning, saving data, and setting coordinate systems. Initially perform experiments in your company premises or other safe locations and verify errors against known control points to understand device performance. Trial operation on a small site to identify data flows and points to note is recommended.

• Integrate into workflows: Incorporate RTK survey data into actual work processes. For earthwork volume calculations, determine how to import data into point cloud processing or volume calculation software. For as-built management, align RTK output with existing record formats (for example, prepare spreadsheets that automatically calculate height differences when coordinate data are pasted). Ensure data backup and establish a system for sharing via cloud storage or internal servers.

• Start operation and follow-up: Once you start using RTK receivers on site, conduct regular follow-ups. For a while, compare positioning results with those from traditional methods to confirm acceptable accuracy. Continuously solicit feedback from field staff to identify further efficiency gains and refine procedures. If you later obtain internal success stories (e.g., percent reduction in schedule, labor cost savings), these can support wider rollout and additional adoption.

These are the basic implementation steps. If unsure during selection, arrange a hands-on demo or gather other companies’ case studies. Opportunities to try operating RTK equipment at construction DX exhibitions and seminars are increasingly available and are useful to take advantage of.

Practical workflow for obtaining point cloud control points via smartphone surveying using LRTK

Here, we introduce a concrete workflow for obtaining point cloud control points (control points) for drone photogrammetry and similar tasks using the smartphone RTK receiver "LRTK." LRTK is a smartphone-integrated RTK system; by attaching a dedicated receiver to a smartphone device, anyone can easily achieve centimeter-level positioning. Using LRTK, control point surveying for drone point clouds can be performed with a smartphone in hand, enabling rapid acquisition of high-precision point cloud data.

STEP 1: Preparation for the site Prepare the LRTK receiver unit and a smartphone (or tablet) with the LRTK-compatible app installed. Upon arrival, dock the smartphone and receiver and power them on. Because LRTK is powered by an internal battery, complicated wiring is unnecessary.

STEP 2: Connect to correction information Set up RTK positioning in the smartphone app. If the communication environment is good, enter Ntrip (network reference station service) account information in the app to receive correction data. If the site is in a mountainous area or otherwise has poor communications, switch the LRTK to the Michibiki CLAS mode that LRTK supports to receive augmentation signals from satellites. Once settings are complete, the app displays the current positioning mode (float solution or fixed solution); when it shows "Fix" within a few tens of seconds, centimeter-level positioning has started.

STEP 3: Measure control points Measure control points that will serve as references for the point cloud data. Place identifiable targets (artificial markers) on the ground beforehand, then position the LRTK receiver over them to take measurements. Tap "Start Positioning" in the smartphone app to record the latitude, longitude, and height at that moment. To improve accuracy, use the app’s averaging function to average data for about 5–10 seconds to determine a stable coordinate value. Save point names and notes for each control point to facilitate later data processing.

STEP 4: Save and share data Measured control point data are saved on the smartphone and can be uploaded to the cloud with one button. By using the LRTK cloud service, coordinates measured on site can be checked immediately from an office PC. After measuring all control points, review the data in the app and, if necessary, recheck positions on the map—for example, verify that no wrong points were measured and that the number of recorded points matches the number of targets.

STEP 5: Use in point cloud processing Import the obtained control point coordinates into drone photogrammetry processing software. Specifically, designate these control points as GCPs (Ground Control Points) during aerial image processing to align the model’s coordinates. Coordinates obtained with LRTK are already converted to high-precision global geodetic or plane rectangular coordinates, so they match in the software without offset. This ensures that the generated point cloud is tied to an accurate coordinate system such as the Geospatial Information Authority of Japan’s standard, producing a high-quality 3D model ready for as-built management and quantity calculations.

This is the workflow for control point surveying using LRTK. Tasks that previously required a GNSS receiver plus controller can now be completed with just a smartphone, eliminating transcription errors and extra steps. Even technicians with limited surveying experience can operate intuitively, greatly reducing on-site burden and speeding up work.

On-site use cases (stake setting, photogrammetry, AR navigation, volume calculation)

Introducing RTK receivers has led to new use cases on site across various scenarios. Below are major use cases and how they contribute to efficiency and sophistication.

• Stake setting and layout marking: Stake setting and layout marking require accurate coordinates on construction sites. Using an RTK receiver, coordinates from design drawings can be reproduced directly on site. Specifically, workers move while viewing the difference between their current position and the target coordinate on the smartphone screen, and when the positions match, they drive a stake or apply marking paint. Traditionally, a surveyor with a total station and an assistant holding a prism were required, but RTK enables one person to set multiple points in a short time. RTK is especially effective in open development sites or long road alignments, reducing staking errors and rework.

• Photogrammetry (drone and ground imaging): High-precision, geotagged images are important in drone photogrammetry and ground-based imaging. RTK can be used in two ways: RTK-equipped drones or cameras record corrected coordinates at the time of capture, or multiple control points measured with RTK within the imaging area are used to correct the photogrammetric model during processing. Either approach significantly improves the accuracy of the resulting point cloud model. As a result, trustworthy 3D models for volume calculation and as-built verification can be produced quickly. Increasingly, site supervisors themselves use tablets and RTK to perform simple photogrammetry, making frequent acquisition and use of 3D point clouds part of routine operations.

• AR navigation and visualization: Centimeter-level RTK accuracy combined with AR (augmented reality) opens new possibilities. For example, if design position data exist for buried pipes or cables, those positions can be overlaid on the smartphone or tablet camera view to visualize otherwise invisible infrastructure on site. Because RTK specifies the device’s real-world position and orientation with high precision, misalignment between digital data and reality is minimized, bringing AR guidance to practical levels. Virtual flags can be placed at stake locations and displayed in AR for workers to follow intuitively. In as-built management, heat maps of deviations from design can be overlaid on actual structures in AR to identify defects on the spot. RTK receivers provide the positional accuracy that underpins these AR-based on-site management applications.

• Volume calculation and as-built quantity management: In earthworks and land development, managing fill and excavation volumes is central to schedule and cost control. RTK receivers greatly streamline volume measurement and calculation that previously took days. For example, one can walk around a spoil heap with an RTK-equipped smartphone to scan a point cloud and immediately compute its volume. The resulting figures can be checked on site, answering questions like “how many truckloads remain” or “how many cubic meters short are we compared to plan.” This enables agile revision of hauling plans and quantitative daily tracking of progress to share with clients. Accumulated measurement data can also serve as 3D evidence for final as-built quantities. High-precision volume calculations using RTK receivers directly improve and speed up site construction management.

Conclusion: Outlook for efficiency and high-precision management using RTK receivers

Introducing RTK receivers is a trump card for dramatically improving productivity and measurement accuracy on construction and surveying sites. High-precision measurement that once depended on specialized departments or outsourcing is increasingly being performed daily by field staff themselves. As a result, workflows that instantly digitize all as-built data and reflect it in on-site decision-making are becoming reality. RTK receivers—particularly the new generation that integrates with smartphones—are technologies that could see "one-per-person" adoption, and in the future each worker may carry their own surveying tool to precisely understand every corner of a site.

This trend will transform the construction PDCA cycle. For example, checking the previous day’s as-built point clouds each morning and revising construction plans accordingly allows for reduced rework and material waste. Increased survey frequency and coverage also enable early detection and immediate correction of construction errors and defects, preventing quality issues from propagating. From a safety perspective, remote measurement of hazardous areas and guidance for heavy equipment operations can reduce accident risk.

As 3D data utilization expands further, site visualization and DX (digital transformation) are expected to accelerate. The fusion of high-precision GNSS technology and digital tools will update construction management with unprecedented efficiency and accuracy. Consider the benefits of introducing RTK receivers: the prospect of both streamlined field operations and high-precision management is within reach.

FAQ: Frequently asked questions about RTK receivers, positioning accuracy, and point cloud data integration

Q1: What is the difference between an RTK receiver and ordinary GPS? A1: Ordinary GPS typically has errors on the order of meters, whereas RTK receivers use correction information from a reference station to achieve centimeter-level positioning. Because RTK cancels errors in real time, it provides accurate coordinates on the spot. For example, a regular GPS may give different positions when measuring the same point repeatedly, but RTK yields nearly identical values, ensuring the accuracy needed for as-built management and comparison with design drawings.

Q2: Is a base station always required for RTK positioning? A2: It is not always necessary to set up your own physical base station. Using network RTK services (VRS or Ntrip streams from reference stations, etc.) allows a single rover receiver to perform positioning. In Japan, using Michibiki’s CLAS is another option; compatible receivers can obtain correction information without an Internet connection. However, deploying your own base station can provide accuracy optimized for your construction area, so base station + rover setups are sometimes used on large sites.

Q3: How reliable is RTK positioning accuracy on construction sites? A3: Properly operated RTK typically achieves planar errors of around 2–3 cm and elevation within about 5 cm. In open environments with minimal obstructions, higher accuracy is possible; static measurements averaged over time can reach sub-centimeter accuracy in some cases. However, accuracy degrades under structures such as overpasses or under trees where GNSS signals are disturbed, so complementary use of total stations or other instruments may be necessary. In general, RTK receiver accuracy is sufficient for as-built management and earthwork volume calculations, but for structural measurements requiring millimeter precision, combining with laser scanners may be appropriate depending on the case.

Q4: How do you align point cloud data obtained with an RTK receiver to design data? A4: By using an RTK receiver, point cloud data are assigned accurate coordinates, so they can typically be overlaid directly onto the design coordinate system. For example, if design data are in a public coordinate system (plane rectangular coordinates), RTK-acquired point clouds in the same system can be compared without special transformation. If survey coordinate systems differ, georeferencing using known control points to translate and rotate the point cloud can resolve differences. Compared to pre-RTK workflows, aligning point clouds to design data has become considerably easier.

Q5: Are special qualifications or licenses required to introduce RTK receivers? A5: Operating an RTK receiver itself does not require special licenses; anyone can use it. However, if you operate your own base station and use radio equipment, a radio station license may be required depending on the wireless device used (many commercial RTK systems use license-exempt low-power radios or Bluetooth, so no license is needed). Also, using network RTK services requires a contract with the service provider. Manufacturers and dealers often provide training, so it is advisable to take such courses when introducing equipment for the first time.

Q6: Can a smartphone’s GNSS achieve RTK-like high-precision positioning? A6: Recent smartphones include high-performance GNSS chips, and some can obtain raw observation data for RTK processing. However, the small internal antennas in smartphones limit reception sensitivity, so obtaining stable centimeter-level accuracy solely with the phone is still difficult. Connecting a dedicated RTK receiver (antenna) to the smartphone allows robust satellite signal reception and high-precision positioning. Therefore, the smartphone + external RTK receiver combination is the best choice for balancing convenience and accuracy. Smartphone-integrated devices like LRTK maintain smartphone usability while delivering survey-grade accuracy, which is why they are increasingly used on sites.