Streamline Civil Construction Sites with Drone Surveying! 3 Cutting-Edge Technologies That Can Cut Survey Time by 50%

In civil engineering sites, surveying and measurement have traditionally required significant time and manpower. For topographic surveys of large development sites and volume calculations, survey staff often had to walk the site for days to collect a large number of control points. Drone surveying has attracted attention as a trump card to eliminate such inefficiencies. 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 (about a 50% reduction). Moreover, because drone survey data are high-density and detailed, more precise analyses than before become possible, and the ability to cover wide areas in a single flight is another attractive efficiency.

Within the Ministry of Land, Infrastructure, Transport and Tourism’s *i-Construction* initiative, the use of new technologies such as drones and laser scanners to improve productivity is strongly encouraged. Drone surveying has already begun to be adopted at many construction sites, with significant effects reported such as substantial reductions in survey time, improved safety, and compensation for labor shortages. This article introduces three of the latest drone surveying technologies that can improve efficiency in the civil engineering field. For each technology, we explain concrete use cases, points for implementation, benefits, and cautions, clarifying why drones are effective for productivity innovation on civil works sites.

1. Drone Photogrammetry

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

Use Cases

• Topographic surveys of development sites and construction sites: Suitable for grasping current topography and terrain changes before and after development on large sites. Aerial drone imaging can create detailed topographic models of land areas on the order of tens of hectares in a short time.

• Volume calculation and quality control: For monitoring excavation and embankment progress, volume calculations can be performed using point cloud data and orthomosaic images obtained from drone photogrammetry. It can capture subtle undulations that manual surveys may overlook, streamlining checks of as-built conditions and earthwork quantity management.

• Infrastructure inspection and disaster surveys: Used for inspecting structures such as bridges and dams, and for investigating damage after landslides or floods. Drones can safely record detailed information from above in areas that are dangerous or difficult to access.

Implementation Points

When implementing photogrammetry, high-quality aerial images and appropriate analysis software are key. First, select an industrial-grade drone that can maintain stable flight and equip it with a high-resolution camera. Using an automated flight plan to capture highly overlapping photos produces more accurate 3D models. After shooting, generate point clouds and orthomosaics from the images using photogrammetry software (e.g., Pix4D, RealityCapture, etc.). As a point for improving accuracy, if the drone is not RTK-equipped, place ground control points (GCPs) on the ground and survey their coordinates so you can correct and align the resulting model to real-world coordinates during processing. It is also reassuring to plan flight altitude, photo overlap, and number of control points with reference to official guidelines such as the Geospatial Information Authority of Japan’s "UAV Use in Public Survey Manual (draft)."

Benefits

• Dramatically improved work efficiency: Because drones capture imagery from the air over an area, a single flight can cover wide expanses. For example, a survey of about 10 hectares that used to take several days can sometimes be completed in 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, yielding much denser measurement information than manual surveys. As a result, you can accurately capture subtle ground undulations and small cut-and-fill volumes. The orthophotos obtained can be used as detailed aerial maps, and contours or cross sections can be generated freely from the point cloud.

• Cost reduction: Surveys finish in less time and require fewer personnel, reducing labor costs. Compared with aerial surveying using helicopters, equipment and fuel costs are much lower, enabling low-cost, high-precision surveying.

• Improved safety: Drones can photograph hazardous areas such as steep slopes or cliffs remotely, reducing the need for surveyors to enter dangerous spots and lowering the risk of occupational accidents. They also help ensure safety by enabling overhead monitoring of sites where heavy machinery is operating, allowing work separation.

Cautions

• Dependence on weather and environmental conditions: Drone photography cannot be carried out in rain or strong winds, so schedules are subject to the weather. Photogrammetry uses visible-light cameras, so it is not suitable for surveying ground surfaces covered by dense vegetation (the ground under trees cannot be captured). In forests, it may be necessary to combine photogrammetry with laser surveying, discussed later.

• 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 watch your storage capacity. Consider operational burdens such as battery management and maintenance of the drone, and flight authorization procedures (aviation law requirements).

• Accuracy verification: The accuracy of photogrammetric data depends on flight altitude and image-processing quality. For critical surveys, it is recommended to measure a few verification points on site and compare them with the produced data. Also, if you reduce initial investment by using non-RTK drones, you will need to install ground control points, so account for that effort.

2. Drone Laser Surveying (LiDAR)

Laser surveying (LiDAR surveying) mounts a laser scanner (LiDAR sensor) on a drone and directly acquires point cloud data by measuring distances from the time of flight of laser pulses. Previously, airborne laser measurements were mainly conducted from crewed aircraft, but recently drone-mounted LiDAR systems have emerged, making high-density 3D surveying more accessible. LiDAR can capture terrain in conditions where photogrammetry struggles, so its use has expanded in specialized applications.

Use Cases

• Topographic surveys in forests and heavily vegetated terrain: LiDAR’s greatest strength is that laser pulses can reach the ground through gaps in vegetation, allowing measurement of terrain beneath trees. For forest road planning and mountain slope works, LiDAR point clouds can accurately capture ground shapes that are not visible in photos.

• River and erosion control surveys: LiDAR is powerful where broad, high-resolution topographic data are needed, such as measuring elevations on riverbeds and understanding the topography of debris-flow-prone areas. Laser surveying can capture ground forms under grass and brush on riverbeds and the details of collapsed terrain.

• Shape measurement of structures: Used to 3D-scan complex objects like the underclearance of bridge girders, tunnel portals, and steep rock faces. Targets that are difficult for photogrammetry due to shadows or reflections may yield accurate shapes with LiDAR point clouds.

Implementation Points

To introduce drone LiDAR surveying, you need high-performance LiDAR equipment and a compatible drone. Because LiDAR units are heavy, an industrial drone with sufficient payload capacity and flight stability (large multirotor or VTOL fixed-wing) is recommended. Examples include LiDAR modules mounted on DJI’s Matrice series (Zenmuse L1, etc.) and integrated LiDAR drones from overseas manufacturers. Since the combined cost of the aircraft and LiDAR sensor can amount to several million yen, if in-house acquisition is difficult, consider contracting a surveying company or renting equipment.

The measurement workflow is similar to photogrammetry: the drone automatically flies the area while LiDAR emits laser pulses and collects return data. A key point in implementation is performing GNSS corrections to maintain coordinate accuracy of the acquired point cloud. Many LiDAR-equipped drones support RTK/PPK, and the aircraft’s trajectory logs are post-processed to apply positional corrections to the point cloud. This yields a georeferenced 3D point cloud with centimeter-level accuracy. Use dedicated software for LiDAR point-cloud filtering and ground-surface extraction to remove unnecessary points (vehicles, people, noise) and create a digital terrain model (DTM).

Benefits

• Can capture terrain under vegetation: LiDAR’s biggest advantage is its ability to detect terrain beneath forests and ground covered by grass that photogrammetry cannot measure. Because laser pulses perform tens of thousands to hundreds of thousands of range measurements per second, LiDAR can rapidly and densely reproduce broad areas in high accuracy (accuracy on the order of centimeters). This dramatically improves data acquisition where manual surveying was previously difficult, such as in forest civil works and erosion control planning.

• Immediate point cloud acquisition: While photogrammetry requires image processing after aerial photography to generate point clouds, LiDAR accumulates point cloud data during the flight. Post-processing time is relatively short (focused on filtering and coordinate correction), and it is sometimes possible to generate a 3D terrain model the same day. This is effective for disaster site rapid assessment where quick data use is required.

• Both accuracy and coverage: LiDAR point clouds are obtained by direct distance measurements, so dimensional errors are small and accuracy is stable. Because data can be acquired at grid intervals of several centimeters, LiDAR combines survey precision and spatial coverage. You can record an entire slope from its overall shape down to fine irregularities in a single pass, improving the accuracy of volume calculations and terrain analysis.

• Applicable to diverse analyses: The acquired point cloud includes not only the ground surface but also surface objects (trees, buildings), allowing post-processing separation of ground and vegetation for analysis. Applications include measuring tree heights, estimating forest biomass, and managing vegetation around infrastructure (e.g., determining tree heights under power lines).

Cautions

• High initial cost: Drone LiDAR equipment is very expensive, and initial investment barriers are higher than for camera-based photogrammetry. Aircraft plus LiDAR sensor can range from several million to tens of millions of yen, so carefully consider return on investment. Operating LiDAR also requires specialized knowledge, so smaller companies may find it more practical to use external surveying services.

• Operational load on the aircraft: Adding LiDAR increases aircraft weight and battery consumption, shortening flight time. For wide-area surveys, you may need multiple battery changes and takeoffs/landings, and very large-scale surveys (hundreds of hectares or more) can sometimes take longer, so assess the applicable range carefully.

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

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

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

Recently introduced RTK-equipped drones can further streamline surveying by providing centimeter-level positioning accuracy on the drone itself. RTK stands for Real Time Kinematic, a method for instant correction of satellite positioning errors between a base station and a rover (the drone). RTK-enabled drones tag photos and point cloud data collected in flight with high-precision position information, allowing reduced post-processing and simplified ground control point requirements.

Use Cases

• Sites where placing control points is difficult: In mountainous or hard-to-access areas where deploying and surveying ground control points (GCPs) is difficult, RTK drone aerial surveying is effective. With high GNSS accuracy on the drone, you can accurately reference survey data to map coordinate systems with minimal known points.

• Speeding up as-built surveys: As-built management during construction requires frequent surveys, but RTK drones allow quick surveys without placing GCPs each time. For example, regular topographic surveys and volume measurements for roadworks can be carried out quickly by site staff.

• Precision-critical surveying tasks: RTK drones are also useful for land surveys and boundary confirmation where accuracy is important. If the drone is connected in real time to known control points beforehand, the acquired coordinates can be compared directly with design drawings or existing survey maps, producing reliable survey deliverables without additional corrections.

Implementation Points

To use RTK-equipped drones, you need not only the drone but also a base GNSS receiver or a network RTK service. Representative RTK drone models include DJI Phantom 4 RTK and Matrice 300 RTK + P1 camera, which have RTK modules built in. In operation, place a known-coordinate base station (such as a D-RTK2 GNSS antenna) near the flight site or connect the aircraft to VRS base station services provided by carriers or private companies to receive real-time correction data. As an implementation tip, when using a base station, pre-measure its exact coordinates (for alignment to public coordinate systems, derive from active control stations). When using network RTK, verify communications (mobile signal) and note that in mountainous areas, models that can receive Michibiki’s CLAS augmentation signal can maintain corrections even outside conventional mobile coverage.

Data collected with an RTK drone already have high-accuracy coordinates attached, so processing the data in analysis software yields high-precision 3D models and orthophotos with little extra effort. This can eliminate tasks once required (numerous GCP placements and lengthy post-processing), making it realistic to obtain deliverables on site the same day.

Benefits

• Significant reduction in ground work: The biggest advantage of RTK drones is reducing the number of ground control points traditionally required. In extreme cases, aerial photogrammetry can be completed with only one or two verification points. This simplifies pre- and post-survey setup and takedown, significantly shortening total work time.

• Improved accuracy and reproducibility: Real-time corrections record each observation point on the drone with errors within a few centimeters relative to a global positioning reference. Data from different days can be accurately overlaid, enabling high-precision time-series comparisons and progress management. Survey results are reproducible, providing consistent quality when additional surveys are conducted.

• Streamlined data processing: Without RTK, geo-referencing photogrammetry data in post-processing can be time-consuming, but RTK-enabled systems place images automatically in the correct positions in software. Workflows become more efficient, making it easier for operators with less expertise to achieve high-accuracy results.

• Labor-saving and immediate sharing: RTK drones allow a single operator to perform sophisticated surveys, helping address labor shortages. Data captured can be checked immediately on a tablet or PC in the field, enabling quick decisions about additional flights or re-shoots. Uploading data to the cloud allows real-time sharing with office staff.

Cautions

• Aircraft cost and operating expenses: RTK models are generally more expensive than regular drones, and there are additional costs for base station equipment and communications services. Some commercial network RTK services require monthly subscription fees. Estimate cost-effectiveness before introduction and ensure the investment matches project scale.

• Environmental impacts on accuracy: RTK uses satellite signals, so it performs best in open skies. In downtown areas with tall buildings or dense forests, satellite reception can degrade, causing accuracy loss or positioning outages. Be mindful of radio interference and multipath effects. Use conventional methods or check surveys as needed.

• Initial system setup: Using an RTK system for the first time requires specialized initial adjustments, such as setting base station coordinates and linking the drone to the base station. Incorrect reference values will shift the output coordinates, so seek expert support or thorough training before full operation. Also prepare recovery procedures in case RTK service temporarily fails due to firmware updates or service outages.

• Legal and radio licensing: If using a dedicated radio link for RTK between the drone and base station within Japan, a separate 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 purchased equipment complies with domestic radio-law specifications.

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

As introduced above, aerial drone surveying is a powerful means of acquiring wide-area 3D data in a short time. At the same time, new surveying methods using smartphones have emerged to improve on-site efficiency. One notable technology is LRTK (Low-cost RTK), which performs centimeter-level positioning by attaching a compact GNSS receiver to a smartphone. Also called *LRTK Phone*, this solution achieves lightweight surveying with a smartphone + GNSS, obtaining positioning accuracy comparable to dedicated survey instruments by attaching an RTK-GNSS module to an iPhone or Android device.

The main advantage of LRTK smartphone surveying is its simplicity and mobility. Using a smartphone that fits in a pocket, a single person can easily acquire measurement points, greatly reducing the traditionally two-person GNSS survey team. Heavy tripods and mounting rigs are unnecessary—simply go to the measurement point with a smartphone and press a button on the screen to record coordinates. Acquired data can be shared to the cloud in real time, allowing results to be communicated to the office from the field or additional measurement instructions to be received, accelerating the workflow.

This smartphone surveying (LRTK) further boosts site efficiency when combined with drone surveying. For example, measure one known point on site with LRTK before conducting drone photogrammetry and use it to correct the drone’s coordinates for higher-precision aerial surveys. If you need to verify a specific point on a 3D model created by the drone, use LRTK to navigate to that point and pinpoint it for marking on the ground. Also, in places where drones cannot fly (narrow urban spaces, indoors, under bridges), smartphone surveying can serve as an alternative. The combination of drones and smartphones allows seamless use of “area-based measurement from the air” and “point measurement from the ground,” thoroughly eliminating idle time in surveying workflows.

Recently, products using LRTK technology have appeared, and the "LRTK Phone" developed by Refixia, a venture originating from Tokyo Institute of Technology, has been attracting attention as a device that turns a smartphone into a pocket-sized all-purpose surveying tool. By integrating smartphone cameras and AR functions, it can handle multiple tasks—position measurement, photo recording, and plan reference—on a single device, strongly supporting on-site digitalization.

Conclusion

We have looked at the three latest drone surveying technologies—photogrammetry, laser surveying, and RTK-equipped drones—and their respective features and implementation effects. What they have in common is their ability to dramatically increase productivity on civil engineering sites, enabling safer and faster construction. Aerial drone surveying can measure wide areas in a short time, reducing survey time by up to half while improving data accuracy. Photogrammetry is easy and versatile, laser surveying is powerful under special conditions, and RTK-equipped drones simplify the surveying workflow itself. By selecting and combining the most suitable methods for the site, a 50% reduction in construction schedule and substantial labor savings are entirely achievable compared with traditional surveying methods.

Moreover, with new on-site tools like smartphone + GNSS LRTK systems, an era is coming when anyone can intuitively perform high-precision surveys. By using drones to overview the entire site from above and smartphones to complement details on the ground, cutting-edge technologies can realize efficiency and quality improvements that overturn conventional wisdom. In an industry facing labor shortages and aging, adopting these digital surveying technologies is an unavoidable trend. Please consider implementing the latest technologies introduced in this article to help create safer and smarter civil engineering sites.