Drone Surveying vs. Conventional Surveying
Drone surveying is a method in which an unmanned aerial vehicle (UAV) equipped with cameras or other sensors flies overhead to capture terrain data. Compared with traditional ground-based total-station (TS) surveying, its major advantages are the ability to gather wide-area data in a short time and to do so with higher safety and efficiency.For instance, there are cases where an area that would take several days to cover with TS surveying—crews walking the site while carrying prisms—can be mapped by drone in only about half a day. A study by Japan’s Ministry of Land, Infrastructure, Transport and Tourism reports that a 0.31 km² survey requiring 45 days with TS methods was completed in just 1.5 days using UAV laser scanning. In other words, drones can capture all necessary data while drastically cutting survey time and manpower.

Moreover, drone surveying allows high-resolution aerial images to be post-processed into 3-D models automatically, streamlining the office work that follows field operations.

This removes the need for technicians to draft drawings manually from individual point data, as is often required with TS surveys. Drones can also fly safely over rugged or disaster-stricken areas where ground crews cannot enter, making data capture possible even in otherwise inaccessible locations.

For these reasons—and buoyed by initiatives such as the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction program—the use of 3-D data gained through drone surveying is drawing growing attention in the construction industry. So, what specific deliverables can you obtain from a drone survey? The three main types are as follows.

• Orthophoto (Orthoimage):
  A seamless, top-down image created by stitching together aerial photographs and correcting them geometrically through orthorectification. Because the distortions present in conventional aerial photos are removed, distances and areas can be measured accurately. Orthophotos are often used as bird’s-eye overviews of entire construction sites for progress tracking and as-built verification.

• Point-Cloud Data:
  A 3-D dataset that represents the surface of the target area as a dense collection of individual points. It is generated either by photogrammetric analysis of drone imagery (SfM) or by laser scanning, reproducing terrain and structures at high point density. Point clouds make it easy to analyze surface-elevation distributions, compute earthwork volumes, and create cross-sections.

• 3-D Mapping / Models:
  Three-dimensional models produced from the captured point clouds or imagery. These may include digital surface or terrain models (DSM/DTM) that replicate landforms, as well as fully rendered models of structures. Such models enable comparison with design data, simulation studies, and on-site visualization through augmented reality.

​

Technology and Advantages of RTK-Enabled Drones
A technology gaining attention for boosting the accuracy of drone surveying is RTK GNSS positioning. RTK—short for Real Time Kinematic—is a real-time, high-precision positioning method that uses GNSS (Global Navigation Satellite Systems). With conventional stand-alone positioning, which relies only on satellite signals such as GPS, positional errors of several metres can occur.

For civil-engineering surveys, that level of accuracy is inadequate. RTK solves the problem by having both a reference station— a GNSS receiver placed at a precisely known location— and a rover receiver on the drone observe the same satellite signals simultaneously. The rover’s position is then corrected in real time using the reference station’s data, reducing errors dramatically. Whereas stand-alone GNSS can be off by several metres, RTK typically brings that down to just a few centimetres. This higher precision greatly enhances both autonomous flight and the reliability of survey results.

An RTK-equipped drone carries a high-precision GNSS receiver and logs its position while receiving correction data during flight. The corrections can be delivered wirelessly from a dedicated on-site reference station, or obtained via network-based RTK services—such as VRS systems provided by NTT, the Geospatial Information Authority of Japan, and others.

In the latter case, you can obtain correction data via the Internet without having to set up a reference station on site, making the workflow simpler. Either way, employing RTK dramatically increases the positional accuracy of the drone-mounted GPS, which in turn directly boosts overall survey precision.

​

So, what concrete benefits do RTK-equipped drones deliver?

1. Higher photogrammetric accuracy and fewer ground control points (GCPs)
In conventional drone photogrammetry, multiple GCPs (ground targets) must be set up and surveyed so they appear in the photos and can be used to correct the model during post-processing. Because an RTK drone records the position of every image with centimetre-level precision, the number of required GCPs can be dramatically reduced—and in some cases the needed accuracy can be achieved with none at all. Sites that have adopted RTK-UAVs report large time savings from skipping most GCP installation while still attaining centimetre-grade surveys, which streamlines as-built checks, volume calculations, and progress monitoring.

​

2. Greater surveying efficiency and cost savings
Beyond the simpler setup, RTK drones fly precise autonomous missions, reducing re-flights and retakes. As long as weather permits, the planned area can be covered quickly, and survey staff can move on to other tasks immediately after data capture. Jobs that once took half a day can often be finished in about an hour, yielding significant savings in labour and equipment costs. Because high-precision positions are available in real time, crews can also relaunch the drone on the spot whenever additional points need to be measured. Overall, RTK drones deliver a substantial reduction in both survey time and total expenses.

​

3. Increased data-accuracy confidence
Survey data obtained with RTK offers much greater assurance in accuracy management. In as-built surveys, for example, errors within a few centimetres are easy to explain to the client and may eliminate the need for supplementary ground checks. High-precision point clouds with minimized error sources are robust enough for detailed comparisons with 3-D design models. This higher reliability speeds up decision-making based on the survey results and supports long-term traceability of project records.

​

Thus, RTK-equipped drones are a technology that unites accuracy with efficiency. Upgrading from “fast but coarse surveying” to “fast and precise surveying” will push on-site digital transformation even further.

​

[Case Studies] Surveying Achievements with Drones + RTK

Below are several examples from sites that have adopted RTK-equipped drones. Results have been reported across a wide range of fields—-from large-scale civil-engineering projects to infrastructure inspections.

​

Case 1: RTK Drone Surveying on a Large-Scale Civil Works Project

At a dam-construction site requiring the management of hundreds of thousands of cubic meters of excavated material, RTK drones were introduced. Previously, cross-section surveys with a total station (TS) were carried out for each work zone to calculate volumes. Weekly drone flights now produce a full 3-D terrain model of the entire site, enabling global volume tracking and progress management in a single step. Thanks to RTK, data accuracy is kept within a few centimeters—well within the tolerance needed for as-built inspections. Survey days per month were cut by more than half, and staffing requirements for survey crews were reduced. Point-cloud data from above also allowed early detection of over-excavation and insufficient fill, contributing to quality control. Site managers say that even on vast jobs they can now “visualize” the terrain in real time and oversee the entire project at a glance.

​

Case 2: Orthophoto Utilization in Expressway Construction

On a new expressway project, orthophotos generated by RTK drone flights were produced regularly to monitor land-development progress and structural placement. High-precision ortho-mosaic maps created from RTK-captured images were overlaid on CAD drawings so that any deviation from design positions could be spotted instantly—particularly for bridge piers, retaining walls, and pavement limits. The wide-area orthophotos also served as shared reference material: at weekly meetings, the latest site overview was displayed to coordinate schedules. Reports that used to require patching numerous photos together are now replaced by a single orthophoto, making explanations easier and earning praise from the expressway authority and local governments. Because RTK provides centimeter-level positioning, distances and areas measured directly on the ortho map match field measurements closely, allowing the image to double as an as-built drawing.

​

Case 3: Railway Track Survey & Point-Cloud Applications

RTK drones are proving valuable in railway maintenance as well. One operator surveyed potential landslide zones along mountain rail lines, acquiring high-precision point-cloud data from drone imagery. Where staff once had to walk the slopes for visual checks, detailed analyses can now be done in the office using the 3-D point cloud—calculating slip volumes or comparing pre- and post-collapse terrain in short order. High positional accuracy from RTK simplified alignment with ground-installed monitoring fixtures. Because the cloud also contains track and catenary-pole geometry, it is used to verify track centerlines and measure clearances between structures and terrain.
In another trial, an RTK drone autonomously flew above the tracks late at night after train operations ended to measure track centerline deviations and gauge width. Aiming for fully unmanned nighttime inspections, the project is still under accuracy evaluation, but early results show differences of only a few millimeters to a few centimeters versus manual surveys—an encouraging step toward practical use. These examples demonstrate that even long, linear assets such as railways can be efficiently assessed by combining RTK drones with point-cloud analysis.

​

Concrete Steps for Introducing RTK-Enabled Drones
When planning to deploy an RTK-capable drone, it is essential to understand in advance the equipment, environment, and post-deployment workflows required. Below, we outline each step in sequence.

●Assess required equipment and costs: The first item to secure is (1) a drone equipped with RTK functionality,(2) A GNSS receiver for the reference (base) station or a subscription to a network-based RTK service,(3) Software and a PC for processing the aerial data.

A wide range of RTK drones is available. Depending on your needs, you can choose a compact model such as the DJI Phantom 4 RTK or Mavic 3 Enterprise (RTK), or a larger, more advanced platform like the Matrice 300 RTK, which can carry multiple sensors. Prices vary from several hundred thousand yen for the airframe alone to several million yen for packages that include high-performance sensors.

If you intend to set up your own base station, you will also need a high-precision GNSS receiver and radio equipment. For greater convenience, you can instead subscribe to a network RTK service—such as NTT’s Ichimill or a VRS service based on the Geospatial Information Authority of Japan’s electronic reference stations—to receive correction data via the Internet.

Regarding software, you will need photogrammetry (SfM) processing tools—such as Pix4Dmapper, Metashape, or DJI Terra—to generate point clouds and orthophotos. Although cloud-based services are an option, if you plan to process the data in-house, be sure to invest in a high-performance PC. The initial outlay is not trivial, but in many cases the resulting savings in labor and project time more than offset the cost.

​

●Survey Workflow: Once the equipment is in place, you need to establish the step-by-step survey procedure. A typical drone-survey workflow runs as follows:

​

1. Pre-flight Planning:
   Confirm the survey area and create a flight plan. Using maps and any on-site reconnaissance, set the flight path, altitude, and speed; for photogrammetry, also define the image overlap. For RTK surveys, choose the base-station location or arrange the network connection in advance. Installing a small number of check ground-control points can be useful for later accuracy verification.

2. Drone Flight & Data Capture:
   At the site, launch the drone and let it follow the autonomous flight path. If you are using RTK, start the base station beforehand—or configure the controller as an Ntrip client—to begin receiving correction data. Make sure the drone reports a fixed RTK solution (“FIX”) before starting the survey. Fly over the entire planned area, taking photos or scans; swap batteries as needed on long missions.

3. Data Processing:
   Import the collected imagery into dedicated photogrammetry software and run Structure-from-Motion (SfM) to reconstruct the 3-D model. This generates point clouds, orthophotos, DSMs, and similar outputs. Because RTK positions are already accurate, the results are close to the official coordinate system. Check accuracy against the pre-set control points; if larger errors appear, apply additional georeferencing adjustments in the software.

4. Deliverables & Applications:
   Use the point clouds or orthophotos to create the required products—contour maps, cross-sections, earth-volume calculations, and so on—and overlay them with design drawings or GIS layers for analysis. Deliverables may be supplied as reports or CAD files, and can also serve as documentation for site management. Keep the raw point-cloud data safely stored; it can act as a baseline for future maintenance or inspections.

​

●Operational considerations: When operating an RTK drone, there are several points to keep in mind. First and foremost is compliance with all relevant laws and regulations.Because drone flights are regulated under the Civil Aeronautics Act, you must apply for permission from Japan’s Ministry of Land, Infrastructure, Transport and Tourism (MLIT) and coordinate locally in advance if the survey area falls within restricted airspace. In addition, even survey drones may require a remote‐pilot license depending on their weight and planned flight operations.Next, verify GNSS reception. Because RTK accuracy relies heavily on satellite signals, performance can degrade in environments where satellites are hard to track—such as behind tall buildings or in mountainous terrain. When necessary, set up a temporary base station in an open area or make use of augmentation signals like CLAS from the Quasi-Zenith Satellite System to maintain accuracy.

RTK may also take time to initialize and reach a fixed solution, so it is important to leave the drone stationary for a while before flight and wait until the fix is stable. In photogrammetry, pay close attention to weather and lighting conditions as well. Strong winds can blur images by shaking the drone, and excessive shadows can reduce image-processing accuracy. Whenever possible, choose days with favorable conditions; if that is not feasible, mitigate with HDR shooting or supplementary lighting. Finally, plan for data storage and backups. High-resolution photos consume large amounts of space, so organize the files by project and back them up—e.g., to the cloud—so that required data can be retrieved quickly whenever needed.

​

That is the complete process for introducing RTK drones. There is much to learn at first, but once a workflow is in place, subsequent projects should run smoothly. As your organization builds in-house expertise, you may uncover opportunities to apply the method on other sites or even launch new surveying services.

​

Introduction to LRTK
Finally, let us introduce LRTK, a solution gaining attention for providing high-precision positioning with minimal effort. LRTK is the name of a compact, lightweight, all-in-one RTK-GNSS receiver device and service developed by Lefixea, a start-up from the Tokyo Institute of Technology. This pocket-sized GNSS unit can be attached to a smartphone (primarily iPhone/iPad), supports multi-GNSS and multi-frequency reception, and is equipped with both network-based RTK (Ntrip client) and Japan’s CLAS augmentation signal from the Quasi-Zenith Satellite System. In short, it is a revolutionary device that transforms a single smartphone into a high-precision positioning instrument without the need for specialized surveying equipment.

The key strengths of LRTK are its ease of use and versatility. Install the dedicated LRTK app on your smartphone, enter the correction-service details, tap “connect,” and even a solo operator can start centimeter-level positioning immediately. The workflow is deliberately simple—just switch on Network RTK, set the correction parameters, and begin—so no deep GNSS expertise is required. Any positions or photos you capture can also sync with the LRTK Cloud, enabling instant upload and sharing right from the field.

For example, on a civil-engineering site a surveyor can use a smartphone fitted with LRTK to record the coordinates of as-built features, attach photos, and share everything to the cloud—giving supervisors back at the office real-time access to the data. At the Noto Peninsula earthquake disaster site in January 2024, workers used LRTK phones to measure ground subsidence caused by liquefaction and to pinpoint road cracks, then uploaded the results immediately so all stakeholders could grasp conditions and respond without delay. In this way, LRTK serves as a powerful tool for advancing on-site digital transformation.

New applications of LRTK are already emerging in the construction and surveying sectors. For instance, crews can now take 3-D design models created in BIM/CIM out to the field and, with LRTK’s high-precision positioning, align them accurately for augmented-reality (AR) overlays that let workers verify construction locations on site.

Construction checks that once relied on paper drawings and visual estimation can now be performed intuitively by overlaying 3-D models on a tablet screen, dramatically boosting on-site productivity and accuracy. Because LRTK is a compact device, it can be clipped to a helmet or mounted on a pole, making it easy to use while walking the site for tasks such as surveying, as-built inspections, or staking pile positions. Major general contractors and surveying firms in Japan are already conducting pilot deployments, and the “one GPS surveying device per person” concept is expected to spread rapidly.

​

Why not introduce LRTK—revolutionizing on-site positioning—and start smart surveying that unites accuracy with efficiency?In this article, we have covered everything from the fundamentals of drone surveying and RTK technology to real-world applications and the latest devices.

By incorporating RTK’s high-precision positioning, you can evolve from “fast but rough surveys” to “fast and accurate surveys,” dramatically improving productivity on construction sites and in infrastructure inspections. Take this opportunity to explore RTK drones and LRTK; they are sure to bring new value to your surveying operations.