Streamline Civil Engineering Sites with Drone Surveying! 3 Cutting-Edge Technologies That Achieve a 50% Reduction in Survey Time

In civil engineering sites, surveying and measurement have traditionally required significant time and manpower. Topographic surveys of large development sites and earthwork volume calculations required survey staff to spend days walking the site and acquiring numerous measurement points. As a trump card to eliminate such inefficiencies, drone surveying has attracted attention. By using unmanned aerial vehicles (UAVs) to collect data from the air, the same survey can in some cases be completed in less than half the time of conventional methods (approximately a 50% reduction). In addition, drone-acquired survey data are dense and detailed, enabling higher-precision analysis than before, and the efficiency of covering wide areas in a single flight is also attractive.

Within the *i-Construction* initiative promoted by the Ministry of Land, Infrastructure, Transport and Tourism, the use of new technologies such as drones and laser scanners to improve productivity is strongly encouraged. Drone surveying has actually begun to be introduced at many construction sites, and significant effects such as drastic reductions in survey periods, improved safety, and compensation for labor shortages have been reported. This article introduces three cutting-edge drone surveying technologies that realize efficiency in the civil engineering field. For each technology, we explain concrete use cases, points for introduction, benefits, and cautions, clarifying why drones are effective in transforming productivity at civil engineering sites.

1. Drone Photogrammetry

Photogrammetry is a method in which a high-resolution camera mounted on a drone takes many photos from above the site, and specialized software analyzes the images to produce three-dimensional survey data. It is the mainstream technology in current drone surveying and has been introduced at many civil engineering sites.

Use Cases

• Topographic surveys of development sites and construction sites: Suitable for understanding the current topography of large sites and topographic changes before and after earthworks. Drone aerial photography can create detailed terrain models of areas measuring tens of hectares in a short time.

• Earthwork volume calculation and as-built management: Volume calculations can be performed from point cloud data or orthophotos obtained by drone photogrammetry to manage excavation and embankment progress. It can capture subtle undulations that manual surveying might miss, streamlining as-built confirmation and earthwork management.

• Infrastructure inspection and disaster surveys: Used for structural inspections of bridges and dams, and surveys after landslides or floods. Drones can safely record details from above even in hazardous or hard-to-access areas.

Points for Introduction

When introducing photogrammetry, high-quality aerial images and appropriate analysis software are key. First, select an industrial-grade drone capable of stable flight and equip it with a high-resolution camera. Use automated flight programs to shoot highly overlapping photos to obtain accurate 3D models. After shooting, generate point clouds and orthomosaics from the images using photogrammetry software (e.g., Pix4D, RealityCapture). As a point for improving accuracy, if the drone does not have RTK, place ground control points (GCPs) on the ground and measure their coordinates to correct the model during processing so that the finished model can be aligned to the measured coordinate system with high accuracy. Also, refer to official guidelines such as the Geospatial Information Authority of Japan’s “UAV-based Public Survey Manual (draft)” when planning flight altitude, photo overlap, number of control points, etc., for reassurance.

Benefits

• Overwhelming improvement in operational efficiency: Because aerial imaging covers areas, a single flight can cover a wide area. For example, a 10-hectare survey that traditionally took several days can sometimes be completed in about half a day with drone photogrammetry. Obtaining current 3D data in a short period contributes to shortening the overall construction schedule.

• Detailed, high-precision data acquisition: Drone photogrammetry can acquire point clouds on the order of millions to tens of millions of points, providing point data far denser than manual surveys. As a result, subtle surface undulations and small cut-and-fill volumes can be accurately captured. The resulting orthophotos can be used as detailed aerial maps, and contours and cross-sections can be freely generated from the point cloud.

• Cost reduction: Surveys can be completed in a short time with fewer personnel, reducing labor costs. Compared with airborne surveying using helicopters, equipment and fuel costs are substantially lower, enabling low-cost, high-precision surveying.

• Improved safety: Drones can photograph remotely from dangerous areas such as steep slopes and cliffs where human entry is hazardous. This reduces the need for surveyors to go to dangerous locations, lowering the risk of workplace accidents. Drones also help ensure safety separation by providing an aerial overview even when heavy machinery is operating.

Cautions

• Dependence on weather and environmental conditions: Drone photography cannot be conducted in rain or strong winds, so schedules are affected by weather. Also, photogrammetry uses visible-light cameras and is not suitable for surveying ground surfaces covered by dense vegetation (ground beneath trees will not be visible). In forests, LiDAR surveying described later may need to be used in combination.

• Data processing and equipment management: Processing large numbers of high-resolution photos requires high-performance PCs or cloud services. Point cloud data volumes can be enormous, so pay attention to storage capacity. Also consider operational burdens such as drone battery management and maintenance, and flight permission applications (aviation law procedures).

• Accuracy verification: The accuracy of photogrammetry-derived data is influenced by flight altitude and image processing quality. For important surveys, it is recommended to measure several verification points on site and compare them with the resulting data. Additionally, if you choose to suppress initial investment by using a non-RTK drone, installing ground control points will be necessary, so factor that effort into your plan.

2. Drone Laser Surveying (LiDAR)

Laser surveying (LiDAR surveying) is a method in which a laser scanner (LiDAR sensor) mounted on a drone measures distances from the flight time of laser pulses and directly acquires point cloud data. While airborne laser measurement using manned aircraft was once the mainstream, drone-mounted LiDAR has recently emerged, enabling easier acquisition of high-density 3D surveys. Because LiDAR can capture terrain under conditions where photogrammetry struggles, its use is expanding in specialized applications.

Use Cases

• Topographic surveys in forests and heavily vegetated terrain: LiDAR’s greatest strength is that its laser pulses can pass through gaps in the canopy to reach the ground, allowing measurement of underlying terrain. In planning forest roads or hillside works, LiDAR point clouds can accurately capture ground shapes invisible to photogrammetry.

• River and erosion control surveys: Effective when wide-area, high-detail topographic data are needed, such as elevation surveys of riverbeds and topographic assessments of debris-flow hazard zones. Laser measurements can capture ground shapes of riverbeds covered with grass or scrub and detailed collapse topography.

• Shape measurement of structures: Used for 3D scanning complex objects such as the underclearance of bridge girders, tunnel entrances, and steep rock slopes. LiDAR point clouds can directly capture shapes that are difficult to measure accurately with photogrammetry because of shadowing or reflections.

Points for Introduction

To introduce drone laser surveying, high-performance LiDAR equipment and compatible drones are required. LiDAR units are heavy, so industrial drones with sufficient payload capacity and flight stability (large multirotors or VTOL fixed-wing aircraft) are recommended. Examples include LiDAR modules for DJI’s Matrice series (Zenmuse L1, etc.) and integrated LiDAR drones from overseas manufacturers. Since the cost of the aircraft plus LiDAR sensor can amount to several million yen or more, if in-house acquisition is difficult, outsourcing to survey companies or using equipment rental are options.

The measurement workflow involves automatically flying the area similarly to photogrammetry while the LiDAR emits laser pulses and collects return data. A key introduction point is applying GNSS correction to retain coordinate accuracy of the acquired point cloud. Many LiDAR-equipped drones support RTK/PPK and post-process the aircraft trajectory logs to correct the point cloud positions. This yields georeferenced 3D point clouds with an accuracy of a few centimeters (cm-level accuracy; half-inch accuracy). Use dedicated software for LiDAR point cloud filtering and ground surface extraction to remove unwanted points (vehicles, people, etc.) and create a digital terrain model (DTM).

Benefits

• Ability to capture terrain beneath vegetation: LiDAR’s biggest advantage is capturing terrain inside forests or ground surfaces covered by grass that photogrammetry cannot measure. Laser pulses measure tens of thousands of ranges per second, enabling rapid, high-precision (cm-level accuracy; half-inch accuracy) and high-density 3D reproduction of wide areas. This dramatically improves efficiency for obtaining terrain data that was previously difficult to measure manually in forest civil engineering and erosion-control planning.

• Immediate acquisition of point cloud data: While photogrammetry requires post-processing of aerial images to generate point clouds, laser surveying accumulates point cloud data during flight. Post-processing time is relatively short (mainly filtering and coordinate correction), and in some cases a 3D terrain model can be generated the same day. This is effective for rapid situational assessments in disaster areas.

• Both accuracy and coverage: Because LiDAR point clouds are obtained by directly measuring distance, dimensional errors are small and accuracy is stable. Data can be acquired on a grid spacing on the order of a few centimeters (several inches), enabling both surveying accuracy and spatial coverage. For example, a slope’s overall appearance and minute irregularities can be recorded at once, improving the accuracy of earthwork calculations and terrain analysis.

• Applicable to various analyses: The acquired point clouds include not only ground but also surface objects (trees, structures), so it is possible to separate ground and vegetation later for analysis. Applications include measuring tree heights or estimating forest biomass for environmental analysis, and managing trees around infrastructure (e.g., measuring tree heights under power lines).

Cautions

• High initial cost: Drone LiDAR equipment is very expensive, and the initial cost barrier is higher than camera-based photogrammetry. Aircraft plus LiDAR sensors can range from several million to tens of millions of yen, so carefully consider the return on investment. Operation requires personnel with specialized knowledge, so for small and medium-sized enterprises it may be more realistic to use external survey services.

• Operational load on the aircraft: Adding LiDAR increases aircraft weight and accelerates battery consumption. Flight time is reduced, and for wide-area surveys it may be necessary to land and swap batteries multiple times, which can actually increase time for very large surveys (hundreds of hectares or more). It is important to judge the appropriate application scope.

• Data processing and management: Point cloud files can become very large, requiring high-performance computers and large-capacity storage for analysis and archiving. Extracting useful information from the point cloud requires specialized processing such as noise removal and ground-point filtering. Software proficiency takes time, so consider training or support from specialized vendors if in-house skills are lacking.

• Regulations and flight permissions: LiDAR-equipped drones tend to be larger, and depending on weight and flight methods may require flight permissions and additional safety measures from the Ministry of Land, Infrastructure, Transport and Tourism. Since operations often involve beyond-visual-line-of-sight or night flights, understand required procedures in advance and enforce safe flight management.

3. RTK-Equipped Drones (High-Precision Positioning Drones)

The recently introduced RTK-equipped drones are a cutting-edge technology that can further streamline surveying by giving the drone centimeter-level positioning accuracy. RTK stands for *Real Time Kinematic*, a method that instantly corrects satellite positioning errors between a base station and a rover (the drone). In RTK-compatible drones, photos and point cloud data captured during flight are tagged with high-precision position information, allowing simplification of post-processing and ground control point setup.

Use Cases

• Sites where placing control points is difficult: In mountainous or hard-to-access areas where installing and surveying ground control points (GCPs) is difficult, RTK drones enable effective aerial surveying. High GNSS accuracy allows survey data to be accurately positioned in map coordinates with minimal known points.

• Speeding up as-built surveys: As-built management during construction requires frequent surveys, but RTK drones enable rapid surveying without installing control points each time. For example, site staff can quickly perform regular topographic surveys or earthwork measurements for road construction.

• Surveys where accuracy is essential: RTK drones are useful for land surveys and boundary confirmation where accuracy is critical. If the drone is connected in real time to known reference points, the acquired coordinate values can be compared directly with design drawings or existing surveys without additional corrections, yielding highly reliable results.

Points for Introduction

Using RTK-equipped drones requires not only the drone but also a GNSS receiver as a base station or a network RTK service. Representative RTK drones include the DJI Phantom 4 RTK and the Matrice 300 RTK + P1 camera, which have RTK modules built in. During operation, either set up a known-coordinate base station near the flight site (a GNSS antenna such as D-RTK2) or connect the aircraft to a VRS reference station service provided by NTT or private providers to receive real-time correction information. A tip for introduction is to accurately measure the base station’s coordinates in advance if using a local base station (for aligning to public coordinate systems, derive coordinates from reference stations). If using network services, check communication conditions (mobile signal, etc.); in mountainous areas, a receiver capable of receiving QZSS “Michibiki” CLAS augmentation signals can maintain corrections even when out of cellular coverage.

Data captured by RTK drones already have high-precision coordinates, so processing with analysis software yields accurate 3D models and orthophotos without the usual amount of work. The time-consuming steps of installing many GCPs and lengthy post-processing can be eliminated, making it realistic to produce deliverables on the same day at the site.

Benefits

• Greatly reduced ground work: The biggest advantage of RTK drones is that they can reduce the number of ground control points usually required. In extreme cases, aerial photogrammetry can be completed with only one or two verification points. This simplifies pre- and post-survey setup/teardown and greatly shortens total work time.

• Improved accuracy and reproducibility: Real-time corrections record each observation point within a few centimeters relative to global positioning standards. Data from different days can be accurately overlaid for high-precision time-series comparisons and progress management. Survey results are highly reproducible, providing consistent quality for additional surveys.

• Simplified data processing: Without RTK, georeferencing photogrammetry data required effort in post-processing, but RTK-enabled data are automatically placed in the correct position in software. Workflows are streamlined, enabling even operators with limited expertise to produce high-precision results.

• Labor savings and immediate sharing: RTK drones allow a single operator to perform advanced surveys, addressing labor shortages. Acquired data can be checked immediately on a tablet or PC on site, enabling instant decisions on additional flights or re-shoots, and uploading to the cloud allows real-time sharing with office staff.

Cautions

• Equipment cost and operating expenses: RTK models are generally more expensive than standard drones, and base station equipment and communication service fees may apply. For example, network RTK services may charge monthly fees. Estimate costs and evaluate whether the investment matches project scale.

• Accuracy affected by the environment: RTK uses satellite signals, so it performs best in open skies. In high-rise urban areas or dense forests, signal reception may be insufficient, causing accuracy degradation or loss of positioning. Be mindful of radio interference and multipath reflections. Use conventional methods or check surveys as needed.

• Initial setup: First-time RTK system use requires technical initial setup such as base station coordinate entry and linking the drone to the base station. Incorrect reference values will shift all result coordinates, so obtain expert support or sufficient training before operational use. Also prepare recovery procedures in case RTK functionality is temporarily unavailable due to firmware updates or service outages.

• Legal and radio licensing: If using a proprietary radio link for RTK between the drone and base station domestically, a radio station license may be required. However, many commercial RTK drones receive corrections via existing radio bands or the Internet, so individual licensing is often unnecessary. Confirm that the product complies with domestic radio law at purchase.

Further Efficiency by Combining Drone Surveying with Smartphone Surveying (LRTK)

As introduced so far, drone aerial surveying is a powerful means to quickly acquire wide-area 3D data. At the same time, a new surveying method using smartphones has emerged to further improve on-site efficiency. Particularly noteworthy is LRTK (Low-cost RTK), which uses a small GNSS receiver attached to a smartphone to achieve centimeter-level positioning; it is also referred to as *LRTK Phone*. This solution combines a smartphone with an RTK-GNSS module attachment, enabling positioning accuracy comparable to dedicated surveying instruments.

The main advantage of LRTK smartphone surveying is its ease of use and mobility. Using a smartphone that fits in a pocket, a single person can easily collect measurement points, greatly reducing the manpower compared to the conventional two-person GNSS survey. Heavy tripods and mounting gear are unnecessary—simply bring the smartphone to the measurement point and press a button on the screen to record coordinates. Acquired data can be shared to the cloud in real time, enabling immediate reporting from the field to the office and speeding up workflows with instant measurement instructions.

Combining smartphone surveying (LRTK) with drone surveying further boosts on-site efficiency. For example, before performing drone photogrammetry, measure one known point on the ground with LRTK and use it to correct drone coordinates for high-precision aerial surveying. Also, if you want to verify arbitrary points on a drone-created 3D model on the ground, LRTK can navigate to and pinpoint those coordinates for on-site confirmation and marking. Moreover, in places where drones cannot fly (narrow urban spaces, indoors, under bridges, etc.), smartphone surveying serves as an alternative. The drone＋smartphone combination enables seamless switching between “areal measurement from the air” and “point measurement from the ground,” drastically reducing idle time in surveying workflows.

Recently, products utilizing LRTK technology have appeared. The Tokyo Institute of Technology spinoff Refixia’s “LRTK Phone” has been gaining attention as a device that turns a smartphone into a pocket-sized all-purpose surveying instrument. By integrating with the smartphone camera and AR functions, it can handle position measurement, photo recording, and plan reference, supporting on-site digitalization.

Conclusion

We have reviewed the three main cutting-edge drone surveying technologies—“photogrammetry,” “laser surveying,” and “RTK-equipped drones”—and their characteristics and effects on introduction. What all these technologies share is their ability to dramatically increase productivity at civil engineering sites, enabling safer and faster construction. Drone aerial surveying can measure wide areas in a short time, reducing survey time by up to half while improving data accuracy. Photogrammetry is convenient and versatile, LiDAR excels under special conditions, and RTK-equipped drones simplify the surveying workflow itself. By selecting and combining the optimal methods according to site conditions, a 50% reduction in construction time and significant labor savings compared with traditional surveying work are fully achievable.

Moreover, the emergence of new on-site tools such as smartphone＋GNSS LRTK means that anyone can intuitively perform high-precision surveys. By using drones for aerial overview and smartphones for ground-level detail, advanced technologies can overturn conventional wisdom to achieve unprecedented efficiency and quality improvement. In the civil engineering industry, which faces labor shortages and aging, the adoption of these digital surveying technologies is an unavoidable trend. Please consider introducing the latest technologies presented in this article to help create safer and smarter civil engineering sites.