High-Precision, Simple Surveying Achieved by RTK-Enabled UAV Photogrammetric Point Cloud Generation

Table of Contents

• Spread of drone surveying and utilization of point cloud data

• RTK-GNSS positioning is the key to higher accuracy

• Increased efficiency in point cloud processing through cloud utilization

• What is LRTK? A new surveying method realized with smartphones and the cloud

• Possibilities expanded by simple surveying with LRTK

• FAQ

Spread of drone surveying and utilization of point cloud data

In recent years, aerial photogrammetry using drones (unmanned aerial vehicles: UAVs) has rapidly spread across construction and civil engineering sites. Drone surveying, which captures the site from above to photograph terrain and structures, offers significant advantages over traditional ground surveying: it can cover wide areas in a short time and greatly improves safety and efficiency. There are reports of vast sites that once required people walking for measurements being completed in just tens of minutes to half a day with drone aerial photography. Drones are also attracting attention because they can safely capture current conditions from above in areas people cannot access, such as steep slopes or disaster sites.

Aerial photographs captured by drones can be converted into deliverables such as point clouds and orthophotos using specialized software or cloud services. An orthophoto is a distortion-free photographic map taken from directly above and can be used for overall project overviews and progress management. Point cloud data, on the other hand, are three-dimensional data that reproduce the surfaces of terrain and structures as countless points. By analyzing these point clouds, you can grasp elevation differences of the ground, precisely calculate earthwork volumes, or easily create cross-sections at arbitrary locations. Drones are thus a powerful tool for digitally transforming the entire site, and initiatives like the Ministry of Land, Infrastructure, Transport and Tourism’s "i-Construction" are further encouraging increased use of three-dimensional data in the construction industry.

However, to use digital 3D data as accurate surveying results, ensuring positional accuracy is indispensable. The next section explains the technology that dramatically improves the accuracy of drone surveying.

RTK-GNSS positioning is the key to higher accuracy

As drones have made it easy to acquire wide-area data, ensuring the accuracy of that data has become a major challenge. Even if photos can be easily taken and turned into 3D models, large errors in position or dimensions prevent use as official survey results. Recently, attention has been focused on RTK-GNSS (real-time kinematic GNSS) high-precision positioning technology. RTK refers to a method in which a base station (a GNSS receiver installed at a known coordinate) and a rover (a GNSS receiver mounted on a drone) simultaneously perform satellite positioning and the difference between them is corrected in real time, dramatically improving positioning accuracy. Ordinary GPS positioning can have errors on the order of several meters, but using RTK can reduce errors to within a few centimeters. If a drone is equipped with an RTK-GNSS receiver that supports high precision, it can record its accurate position while receiving correction information during flight. As a result, the positional accuracy of the captured image data improves markedly, and the point clouds and orthophotos generated in post-processing align precisely with map coordinate systems.

There are many benefits to high-precision drone surveying using RTK. First, improving photogrammetric accuracy can drastically reduce the number of ground control points (GCPs) placed on the ground. Traditionally, creating precise 3D models from drone photos required surveying multiple reference points in advance and including them in photos to use for georeferencing. However, with an RTK-enabled drone, the positional information recorded in each photo is initially accurate to within a few centimeters, so in some cases the required accuracy can be met with zero GCPs. In practice, some report that after introducing RTK drones, the work of installing GCPs became almost unnecessary and the time required for survey preparation was greatly reduced. Even so, the resultant point clouds and photos are extremely accurate, making as-built checks, earthwork calculations, and progress management much more efficient.

Second, overall surveying efficiency and cost reduction. RTK drones not only reduce time-consuming preparation, but because flights can be automated and executed accurately, the risk of reflight or retakes is reduced. If the weather is favorable, the planned area can be captured in a short time in a single flight, allowing survey personnel to move on to the next task immediately after data acquisition. There are cases where site surveys that used to take half a day are completed in about an hour, producing significant savings in labor and equipment costs. Because high-precision positions are obtained in real time from the drone-mounted GPS, if you decide “I want to measure this additional point,” you can immediately fly the drone and collect the data—enabling flexible operations. Upgrading to faster and more precise surveying will dramatically improve on-site productivity.

Increased efficiency in point cloud processing through cloud utilization

Recently, cloud processing services for photos acquired by drones have emerged, advancing the efficiency of point cloud generation and data sharing. Traditionally, processing a large number of images into point clouds required a high-performance workstation and specialized software. By using cloud photogrammetry services, however, you can upload images from the field via the Internet and automatically generate point clouds and orthophotos. Heavy processing is handled in the cloud, so a weak local PC is not a problem. Even without purchasing dedicated viewer software, the generated products can be reviewed in a web browser, making it easy for anyone to handle 3D data.

There are further advantages to using the cloud. Uploaded data is stored online, enabling simultaneous sharing among internal team members. For example, when images captured by a drone at the site are sent to the cloud, office staff can immediately view the point clouds and begin necessary analyses—achieving real-time collaboration. Data are organized and accumulated by date and project, making it easy to review progress later or reference past survey results. Large point cloud datasets that might exceed the capacity of local PCs or servers can be stored and managed in the cloud without worrying about storage space. Additionally, because you do not need to purchase and maintain expensive hardware or software in-house, there are cost advantages. By utilizing cloud services in this way, an environment is being established where 3D data obtained from drone surveying can be used more easily and effectively.

What is LRTK? A new surveying method realized with smartphones and the cloud

As described above, combining drones × RTK × cloud processing can efficiently produce high-precision three-dimensional survey data. However, when trying to apply this at actual sites, you might hesitate, wondering “Do we need to prepare expensive RTK-equipped drones and dedicated software?” To lower such hurdles and enable anyone to easily perform high-precision surveying, LRTK was developed. LRTK is an integrated solution developed by a startup originating from the Tokyo Institute of Technology, consisting of a compact RTK-GNSS receiver, a smartphone app, and cloud services that work together. In simple terms, “a smartphone instantly becomes a high-precision surveying instrument, and the acquired data is managed and analyzed in the cloud,” realizing a new style of surveying.

The compact receiver device at the heart of LRTK fits in a pocket yet is equipped with a high-performance multi-band GNSS module. It can be attached to a smartphone in one touch using a dedicated case-style attachment, with no wiring required. The LRTK device weighs about 150 g (5.3 oz) and is approximately 13 mm (0.51 in) thick, making it very thin and lightweight and unobtrusive when attached to a smartphone. Once this device is attached to a smartphone, the smartphone’s GPS—ordinarily accurate only to within several meters—suddenly upgrades to centimeter-level accuracy (half-inch accuracy). Because it is powered by an internal battery, no cumbersome external power supply is needed. In other words, the moment you attach LRTK to your smartphone, the phone that used to be only for viewing map apps transforms into a “versatile surveying instrument,” ready to be taken to the field for high-precision surveying.

So what specific measurements become possible with LRTK? First is high-precision position measurement. By simply tapping a button on the smartphone screen at the point you want to measure, you can instantly record the latitude, longitude, and elevation of that location. With RTK corrections, errors are kept to within a few centimeters, allowing anyone to obtain accuracy equivalent to traditional benchmark surveying that previously required specialized equipment and skilled operators. The app can also automatically average positioning data, and by remaining stationary and observing for several tens of seconds, it is possible to acquire coordinate values stable to the millimeter order. This potential enables use in advanced surveying tasks such as setting construction reference points or measuring structural displacements.

Next, noteworthy is digital measurement functionality such as point cloud surveying using a smartphone. LRTK works with the smartphone camera and various sensors to record site conditions as 3D data. For example, if you walk around a finished terrain or structure while taking photos with a smartphone in hand, a high-precision 3D point cloud model can be generated from that trajectory and the photos. Point cloud surveying that once required expensive laser scanners can now be easily realized with just LRTK and a smartphone. From the acquired point clouds, distance, area, and volume can be measured, and overlaying CAD design data to check as-built conditions can be smoothly performed in the cloud.

LRTK also supports “LRTK drone” style use, where drone-captured photos are uploaded to the cloud and converted into point clouds. Even if you only have a commercial drone that does not support RTK, you can perform GNSS observations at known ground points with an LRTK device on site, and later correct the geotags of drone photos to generate high-precision point clouds. The ability to obtain high-precision surveying results with an affordable drone by combining it with LRTK—rather than requiring an expensive dedicated RTK drone—is a major attraction.

Furthermore, LRTK integrates with cloud services. Coordinate and point cloud data acquired in the field can be uploaded to the dedicated LRTK cloud from the smartphone with a single tap, and information can be shared with internal team members the moment it is uploaded. Because office PCs can immediately confirm and begin analyzing data, real-time collaboration between field and office eliminates unnecessary waiting time. Data accumulated in the cloud is organized by date and site, allowing it to be referenced as valuable surveying history in the future. In this way, LRTK—combining a small device + smartphone + cloud—opens up the world of high-precision surveying, which used to be handled only by specialists, to general technicians. Its presence can truly be said to be changing the conventional wisdom of surveying on site.

Possibilities expanded by simple surveying with LRTK

Finally, let us touch on the new possibility of “simple surveying” brought by LRTK. Simple surveying with LRTK is the concept of enabling anyone to perform centimeter-level accuracy (half-inch accuracy) measurements routinely, without complicated equipment operation or specialized knowledge. By combining a small RTK-GNSS terminal with a smartphone app, LRTK eliminates the need to carry heavy tripods or perform complex setup. For example, a young engineer who normally specializes in construction management can take an LRTK-equipped smartphone from their pocket and be ready to survey in minutes. They can then measure and record coordinates for required points on the spot one after another. There are surprising reports that terrain surveys that once took an entire day with several people are completed in minutes with an LRTK smartphone scan, earning praise from the field.

If simple surveying becomes a reality, small measurement tasks that were previously outsourced to surveying specialists can be handled by in-house staff, and frequent, high-precision checks of progress and as-built conditions can be carried out. For example, if someone on site needs to know the approximate distance from here to there right away, LRTK makes it possible to measure and share results immediately. In disaster response, LRTK can be powerful for quickly measuring affected areas and providing 3D data to stakeholders for rapid recovery planning. In urban areas where drones cannot be flown, an alternative approach—walking while acquiring point clouds with LRTK—can be considered, further expanding use cases. The traditional assumptions that “surveying should be left to specialists” or “our site can’t handle advanced 3D data” are being greatly overturned by the new simple surveying enabled by LRTK.

The combination of high-precision drone photogrammetric point cloud generation and LRTK will strongly support on-site DX (digital transformation). Lowering the barrier to surveying makes it easier to digitize site conditions more frequently and feed that data back into construction and quality management. That, in turn, directly leads to overall productivity improvement and quality assurance on site. If your workplace hesitates—thinking “we leave surveying to the specialist department…” or “it’s difficult to fly drones here”—consider trying LRTK’s new simple surveying. You will likely experience a transformation of conventional surveying practices.

FAQ

Q1. Do I need specialized knowledge to generate point clouds from UAV photos? A1. If you understand the basic procedures, you can generate point clouds without advanced specialized knowledge. In recent years, cloud photogrammetry services and tools like LRTK have become well developed, allowing you to upload captured photo data and automatically generate point clouds with the push of a button. There are tips for shooting—such as photographing the entire site without omission and ensuring sufficient overlap between images—but AI-assisted apps that help plan shooting are now available, making it easier for beginners to get started.

Q2. Can high-precision surveying be done with drones that do not support RTK? A2. Yes. Even for non-RTK drones, accuracy can be improved using post-processing methods known as PPK (post-process kinematic). For example, you can operate a ground GNSS receiver (such as an LRTK device) during a drone flight to record observation data and later correct the geotags of drone photos. Alternatively, placing several known reference points on the ground and aligning the model to those points after point cloud generation can improve accuracy. Using LRTK makes it easy to acquire reference point data, which helps verify and correct the accuracy of point clouds obtained with non-RTK drones.

Q3. Do I need a high-performance PC or special equipment to process point cloud data? A3. You do not necessarily need to prepare a high-performance PC yourself. As mentioned earlier, cloud services allow vast image datasets to be processed entirely online. Therefore, a high-performance PC is not required. Uploading large amounts of data may take time, but improvements in network environments and cloud-side optimization have made handling such data smoother than before. Regarding security, many services implement measures such as encrypted communication, access control settings, and secure data center management, providing a level of security comparable to managing data on your own servers. If you have concerns, check the service provider’s security policy and track record.

Q4. In what kinds of sites can LRTK be used? A4. LRTK is being used broadly in construction and civil engineering for construction management and as-built surveying, as well as for infrastructure maintenance inspections, disaster scene documentation, and agricultural field management. For instance, at a large dam construction site, weekly LRTK and drone 3D terrain models were created to manage excavation volumes and visualize progress. Local governments have reported cases where staff used LRTK to create 3D records of disaster-affected areas, aiding rapid recovery planning. LRTK is also expected to be utilized in urban planning, environmental surveys, and other fields as an “easy-to-use high-precision surveying tool.” Because it enables simple acquisition of precise 3D data, LRTK is likely to change how surveying is conducted at many more sites in the future.