Drone × LRTK for Wide-Area Surveying! The Latest Point Cloud Utilization Techniques for Land and House Surveyors

Introduction

In recent years, advances in drones (unmanned aerial vehicles) and high-precision GNSS positioning technologies have greatly evolved surveying methods. For professionals involved in surveying, including land and house surveyors, wide-area field surveys that leverage these latest technologies can now be conducted faster, more precisely, and with greater safety and efficiency than before. In particular, by combining point cloud data (a collection of numerous measured points) obtained from aerial photogrammetry with centimeter-level position correction technologies such as RTK and LRTK, it is possible to accurately capture the terrain and structures of vast areas in a short time.

This article explains the characteristics and advantages of acquiring point cloud data via drone aerial photography, an overview of GNSS RTK/LRTK technologies that realize high-precision positioning, and concrete use cases in the practical work of land and house surveyors. It also covers deliverables that can be produced from point cloud data and their practical value, the effects of introducing the latest technologies on work efficiency and safety improvement, and concludes by showing how simplified surveying using LRTK can help with wide-area surveys and improving point cloud accuracy. Please consider this a hint for understanding the latest surveying technologies and applying them to your daily work.

Acquisition of Point Cloud Data by Drone Aerial Photography and Its Characteristics

In photogrammetry using drones, terrain and buildings are photographed from the air as numerous images and those images are analyzed with dedicated software to generate high-density 3D point cloud data. Because data can be collected over an area from above, wide-area site surveys that would take much time on foot can be completed in a short time. For example, when surveying forests or large planned development sites, drone aerial photography can acquire a point cloud of the entire terrain, allowing heights and distances at arbitrary locations to be measured later on a desktop. This dramatically improves efficiency for large-scale field surveys that traditionally took days to weeks.

Point cloud data obtained from drone photogrammetry has the following characteristics and benefits:

• Rapid data acquisition: Because a drone can photograph a wide area at once from above, current-condition data for large properties can be acquired in a short time. Even dense forests, steep slopes, or disaster sites where people cannot safely enter can be surveyed remotely. Survey tasks that previously required several days can in some cases be completed in several hours to half a day, directly shortening overall project schedules.

• High-precision measurement: Drones are equipped with high-resolution cameras and positioning devices, and it is possible to determine 3D coordinates of points from acquired images with an accuracy of a few centimeters (a few in). Structure from Motion (SfM) analysis using numerous photos can produce detailed 3D models and precise orthophotos that faithfully reproduce the terrain. Because the data can achieve accuracy comparable to traditional ground surveying, it can be used as highly reliable survey deliverables.

• Improved cost efficiency: Because wide areas can be covered in a single flight, the need for personnel deployment and for installing many survey points (control points) can be greatly reduced. Especially on large sites, surveys can be completed by a small team in a short time, yielding significant cost savings including labor. For example, earthwork calculations and land surveys that previously took weeks by manual work can be shortened to a few days by combining drones and analysis software.

• Improved safety: With drone surveys, data can be collected non-contact from hazardous areas such as cliffs, valley bottoms, or around buildings at risk of collapse. Terrain and structure information for places that are “needed but cannot be approached” can be obtained without omission, dramatically improving onsite safety.

Drone-based point cloud surveying can be a major aid in the work of land and house surveyors. Note, however, that drone battery endurance is limited, so shooting extremely wide areas may require multiple flights or battery swaps. Also, airspace and time restrictions under aviation law and other regulations, and in some conditions pilot licenses, may be required. Even so, with appropriate planning and technology, drone point cloud surveying can complement or replace traditional methods as a powerful tool.

GNSS Positioning and High-Precision Position Correction with RTK and LRTK

To accurately tie point cloud data acquired by drones or on the ground to precise position coordinates, high-precision position information from GNSS positioning (Global Navigation Satellite Systems) is indispensable. GNSS includes satellite positioning systems from various countries such as the U.S. GPS, Russia’s GLONASS, and Japan’s quasi-zenith satellite system “Michibiki.” Standalone GNSS positioning typically incurs errors on the order of several meters (several ft) due to building reflections and atmospheric effects. This is why smartphone or car navigation GPS can be off by about 5-10 m (16.4-32.8 ft), but such accuracy is insufficient for determining land boundaries or precision surveying.

The technology used to address this is the real-time correction technique called RTK (Real Time Kinematic). RTK uses two GNSS receivers, a base station and a rover: the base station, placed at a known coordinate, sends error information to the rover to correct its positioning, dramatically improving real-time positioning accuracy. Specifically, the base station’s calculated errors are shared via radio or the Internet, and the rover (drone or receiver) applies corrections to its measurements, reducing position error to a few centimeters (horizontal 2-3 cm (0.8-1.2 in), vertical a few centimeters (a few in)). RTK achieves centimeter-level accuracy by using the carrier phase of satellite signals—very short-wavelength signals—and resolving the integer number of carrier wave cycles.

Recently, environments have been established where users can receive RTK correction information without installing their own base stations, such as private correction data distribution services using the Geospatial Information Authority of Japan’s Continuously Operating Reference Stations (CORS) and Japan’s Michibiki centimeter-level augmentation service (CLAS). One example is the latest high-precision positioning solution called LRTK. LRTK combines a compact high-precision GNSS receiver with dedicated apps and services to make RTK positioning easily usable with just a smartphone. LRTK-compatible receivers are mounted on a smartphone and receive correction data via Bluetooth or the Internet to provide the smartphone with high-precision real-time position coordinates. In addition, they support CLAS signals transmitted from Japan’s quasi-zenith satellites, allowing direct satellite-based corrections in areas without mobile communication, thereby maintaining centimeter-level accuracy even in mountainous areas.

By using RTK and LRTK technologies, point cloud data obtained by drone and surveying data collected with a smartphone can be accurately tied to geodetic coordinates. In other words, detailed point clouds acquired over wide areas can be given high-precision positional reference so that survey results conform to mapping coordinate systems. For land and house surveyors, these position correction technologies are powerful tools that significantly enhance the reliability of boundary point measurements and drawing creation.

Practical Use Cases of Drone Point Clouds in Land and House Surveyors’ Work

Combining drone point cloud surveying with RTK/LRTK high-precision positioning yields substantial benefits across many tasks handled by land and house surveyors. Below are representative use cases.

Use in Current-Condition Surveys

In current-condition surveys conducted as a premise for development planning or land-use consideration, drone point clouds are highly effective. Because wide-area terrain and existing structure conditions can be accurately grasped, current-condition surveys that traditionally took more than a few days for plan and elevation measurements can be greatly streamlined. Current-condition drawings derived from the obtained 3D point cloud reflect terrain undulations, the placement of trees and structures in detail, enabling provision of more persuasive materials to planners and clients. Also, if point cloud data itself is archived, additional measurement items that emerge later can often be addressed via desktop work without re-surveying, reducing the need for return visits.

Assistance in Boundary Surveys and Boundary Determination

Drone utilization also plays a supportive role in confirming land boundary points and in boundary determination tasks. While legal procedures such as installing boundary markers and on-site inspections with neighboring landowners remain necessary, aerial images and point cloud data from drones allow a bird’s-eye view of terrain, structures, and vegetation near boundaries. This enables the creation of detailed orthophotos that clearly show the positional relationship between boundary lines and surrounding objects, helping stakeholders reach a common understanding of boundary positions. Overlaying surveyed boundary point coordinates on point cloud data lets you verify boundary-line straightness and relative elevation differences with neighboring land in three dimensions, improving the accuracy of boundary determination drawings. Areas around boundary stakes that are difficult to access can also be understood from the air, reducing the surveyor’s on-site verification burden.

Use in Pre-Design Materials for Land Development

Preparing detailed terrain data before designing residential land development or other development works is extremely important. If land and house surveyors provide high-resolution point clouds and orthophotos obtained by drone, designers and civil engineers can review a 3D model of the site from the office. For example, in development planning, contour maps and longitudinal profiles generated from point clouds help determine how much cut-and-fill is required. Undulations and drainage routes that were traditionally captured through survey maps and site inspection can be modeled without omission from point cloud data, increasing the accuracy of design-stage considerations. Sharing such detailed materials in advance helps prevent rework in design and optimize construction planning.

Deliverables That Can Be Generated from Point Cloud Data and Their Practical Value

Point cloud data obtained by drone aerial photography or mobile surveying is valuable not only as a set of 3D coordinates but also as a source for various processed and analyzed deliverables. Representative deliverables useful in the work of land and house surveyors and related fields include the following:

• Orthophotos: Composite images made from numerous drone photos geometrically corrected into a true top-down photographic map. Orthophotos correspond precisely to map coordinates for every point, allowing distance and area measurements. They are very useful for understanding site conditions and for explanatory materials when overlaid with boundary lines or survey plans.

• DSM/DTM (Digital Surface Model / Digital Terrain Model): Elevation data created by extracting ground and object heights from point clouds. A DSM (Digital Surface Model) represents the surface including buildings and trees, while a DTM (Digital Terrain Model) removes those to represent the bare-earth terrain. These models allow understanding of elevation differences, slopes, and drainage conditions, and are useful for earthwork calculations, development planning, and flood simulations.

• Cross-sections and longitudinal profiles: By drawing arbitrary lines over point cloud data, you can generate cross-sectional shapes along those lines. Creating cross-sections for roads, rivers, or planned development sites aids in evaluating cut-and-fill, designing retaining walls, and confirming elevation relationships with surrounding land. If multiple time-series point clouds are available, pre- and post-construction terrain changes can be compared in section to inspect as-built conditions.

• 3D models: Point clouds can be converted into polygon meshes with textures (photos) applied to produce realistic 3D models. Modeling buildings and structures supports drawing creation for registration filings, cultural heritage recording, and landscape simulations. With the recent rise of BIM/CIM, there is growing demand for using 3D data in design and construction processes.

These deliverables provide visual clarity and detailed information that traditional 2D plans could not deliver. In the work of land and house surveyors, for example, presenting an orthophoto during boundary explanations or using contour and section drawings from point clouds as attachments to development permit applications are increasingly common ways that point-cloud-derived deliverables add value.

Efficiency Improvements and Safety Enhancements from the Latest Technologies

The combination of drone × point cloud utilization and RTK/LRTK high-precision positioning brings significant benefits in both efficiency and safety enhancement to the practical work of land and house surveyors.

On the efficiency side, shortening fieldwork time and shifting tasks to office-based work are major advantages. Because wide-area surveys can be completed in a short time, the surveyor’s travel and time spent placing control points are reduced. By analyzing point clouds in software, required measurement items (distance, area, elevation differences, etc.) can be freely calculated later, eliminating the need to linger on-site for fear of “forgetting” measurements. Since everything is recorded as digital data, additional requests or design changes can often be handled by reprocessing the data without returning to the site. Point clouds and orthophotos are also easy to share and review online with stakeholders, improving meeting efficiency and enabling business continuity via remote work.

Regarding safety improvements, as mentioned earlier, reducing entry into hazardous areas is the most significant point. High places, soft ground, and disaster-affected sites—locations that pose a risk to people—can be safely surveyed from a distance by combining drones and high-precision positioning. Reducing worker burden and lowering the risk of accidents or injuries is a major advantage for corporate safety management. Moreover, automation and digitization of data measurement reduce human error and standardize quality. For example, when multiple people measure the same point and obtain slightly different results, measurements on point cloud data yield identical results regardless of who performs them. This increases reproducibility and reliability of survey results and makes quality assurance at inspection and delivery easier.

Conclusion: A New Era of Wide-Area Point Cloud Surveying Opened by LRTK

Wide-area point cloud surveying using drones and position correction technologies enabled by high-precision GNSS are bringing new possibilities to the work of land and house surveyors. Among these, the emergence of LRTK, which realizes centimeter-precision positioning with a smartphone and compact device, is a revolutionary solution that combines “ease of use” and “improved accuracy.” By adopting LRTK, RTK-level surveying that previously required expensive dedicated equipment and skilled operators can be introduced more accessibly, greatly contributing to precision control in wide-area drone surveys and simplifying cadastral surveys.

For example, georeferencing point clouds obtained by drone can be achieved with high accuracy by using several known points measured with LRTK as references. Also, even on vast sites, LRTK enables positioning while receiving satellite augmentation signals in areas without mobile coverage, allowing stable centimeter-level surveying anywhere. As a result, tasks such as boundary surveys in mountainous areas and infrastructure inspections—where positioning environments were previously limiting—can now be conducted efficiently with high-precision data collection.

Going forward, ICT surveying technologies including Drone × LRTK will continue to evolve and support the role of land and house surveyors. Actively incorporating the latest point cloud utilization techniques will not only improve operational efficiency and service quality but also enhance the ability to handle new projects and differentiate your services. By combining traditional surveying techniques with the latest technologies, let us create further value in future surveying work.