Not just drone surveying! Next-generation 3D construction enabled by LRTK

Currently, initiatives to utilize digital information such as 3D design data and point clouds on-site are increasing, and the way construction is carried out is changing significantly. In recent years, drone-based surveying has become widely adopted on construction sites and is attracting attention as an efficient method for acquiring three-dimensional data. However, next-generation "3D construction" (construction that leverages 3D data) is not realized by drones alone. As a new technology to further promote on-site DX, a high-precision positioning system [LRTK](https://www.lrtk.lefixea.com) that can leverage smartphones has appeared. This article summarizes the overview and challenges of drone surveying while introducing the many functions and use cases provided by LRTK. It explains in detail the possibilities of new 3D construction that does not rely solely on drones and the benefits of introducing LRTK.

Overview, benefits, and challenges of drone surveying

Drone surveying is a surveying method in which a small unmanned aerial vehicle (drone) is equipped with a camera or LiDAR (laser scanner) to acquire site photographs or laser point clouds from the air. As part of the i-Construction initiative, full-scale introduction began around 2016, and now it has become indispensable for quality control of infrastructure work and earthwork volume calculations. Drone surveying, which can acquire 3D data from above in a planar manner, is overwhelmingly more efficient than traditional ground surveying, and its use is spreading across many sites.

The following are some benefits of drone surveying:

• Because it can capture a wide area from above at once, it can acquire high-density survey data in much less time than before

• It enables non-contact, safe measurement of steep slopes and hazardous areas where workers cannot enter

• Accurate 3D models and drawings can be created from the acquired photos and point cloud data and used for quality control and construction planning

• It can be operated with a small number of people, leading to labor savings and time reduction compared to traditional ground surveying

On the other hand, there remain the following challenges in using drones:

• Due to regulations, drones cannot be used in some places where flight is restricted, such as urban areas and around airports

• Flights cannot be conducted in rain or strong winds and are therefore subject to weather conditions

• In confined sites or indoor spaces, takeoff/landing and GPS reception can be difficult, reducing effectiveness

• Operation requires pilot skills and flight permits, and specialized knowledge and preparation are necessary for operation

Diverse approaches to 3D construction

Besides drone surveying, various initiatives that leverage three-dimensional data and digital technologies for "3D construction" are advancing at construction sites. By combining several methods according to purpose and site conditions, efficient construction management is possible. Here are some main approach examples:

• Machine guidance / machine control with ICT construction equipment: A method in which heavy equipment is equipped with GPS and 3D design data to automatically control blade height and slope for construction. This enables high-precision work regardless of the operator’s skill level.

• Terrestrial laser scanners and mobile mapping: Methods that use tripod-mounted laser scanners or vehicle-mounted LiDAR to measure the current state as point clouds. They can acquire millimeter-level precision 3D shapes and are used for detailed measurements of structures and as-built drawing creation.

• Three-dimensional positioning by GNSS surveying or total stations: Surveying instruments using satellite positioning (RTK-GNSS) or EDM to lay out stake positions according to design coordinates or inspect as-built conditions. This is a conventional basic method, but high-precision work requires skilled technicians.

• Use of AR technology: Initiatives that use tablets or smart glasses to overlay design models and drawing information onto the site view. This is effective for sharing the completed image and preventing construction errors, and has been attracting attention recently.

Strengths of LRTK as an alternative and complementary method

LRTK is a new solution developed to complement the various methods described above and make surveying and construction management on-site easier. LRTK, which is used by attaching a small high-precision GNSS receiver (RTK-capable) to a smartphone or tablet, combines smartphone convenience with centimeter-class positioning accuracy (cm level accuracy (half-inch accuracy)). The LRTK device is a compact size weighing just a few hundred grams that fits in the palm of your hand, with the antenna and battery integrated. Therefore, there is no need to carry bulky equipment, and walking around the site while working is easy. Because data is acquired by a person walking directly around the site rather than from the air like a drone, LRTK is powerful even in environments where aerial photography is difficult. In addition, the acquired data can be shared and used instantly in the cloud, and the traditionally separate processes of "surveying" and "construction management" can be seamlessly connected with a single smartphone—another major strength.

In other words, LRTK complements aerial surveying by drones from the ground, and by using both as needed, there are no blind spots in on-site data acquisition. On a large development site, a drone can be used to get an overall topographic overview while LRTK can acquire pinpoint point clouds for details and indoor work. With LRTK filling the situations that were difficult with drones alone, the scope of 3D data utilization will expand further.

Main functions of LRTK and concrete use cases

• High-precision 3D point cloud scanning: By simply holding a smartphone and walking around the site, you can scan surrounding terrain and structures with LiDAR or camera to acquire high-density point cloud data. Because RTK positioning by the LRTK device assigns absolute coordinates to each point, the acquired point cloud can be used directly overlaid on map coordinate systems. For example, if you scan slopes or foundations with LRTK, you can measure dimensions, areas, and volumes on-site without returning to the office. Quality measurements that were previously outsourced to specialists can be performed quickly by on-site personnel with LRTK.

• Design visualization with AR display: Using the AR function of the LRTK app, prepared 3D design models or drawing data can be overlaid on the site view. Because high-precision alignment is possible, models are fixed at the exact position and elevation and do not shift even when you walk around. This enables intuitive sharing of the completed image and on-site checks during construction. For example, before excavation, you can display models of underground buried objects in AR to identify the locations of invisible hazards, or overlay design models during structure construction to check work quality on the spot. Information that was hard to visualize on paper drawings can be conveyed at a glance by overlaying models on the real scene.

• Coordinate guidance (stakeout): LRTK also has a navigation function that guides users to target coordinate points. Arrows and distance information are displayed on the smartphone screen and guide you in real-time as you approach the specified X, Y, Z coordinates. Stakeout and layout positions that were traditionally performed by surveyors with total stations can be completed quickly by anyone using this function. Even reference points buried in vegetation or snow that cannot be found visually can be pinpointed by LRTK if their coordinates are known.

• As-built management and data sharing: Point cloud data and photos acquired with LRTK can be uploaded to the cloud and checked and utilized immediately from office PCs. This allows on-site acquired as-built data to be shared with stakeholders the same day and used for quality checks and progress reporting. Advanced analyses—such as overlaying design data with current point clouds to display deviations with color coding or calculating volume differences for embankment/excavation to determine shortages/excesses—are also automated. Measurements and inspections that previously required large teams after completion can be greatly streamlined and expedited by introducing LRTK.

LRTK use cases where drones are difficult to use

• Confined or small-scale sites: On sites where the construction area is extremely narrow or there are many surrounding obstacles, securing space to fly a drone and preparing may actually be more troublesome. With LRTK, necessary 3D surveying can be completed simply by the person in charge walking and measuring, even on such small sites. There is no problem if there is no takeoff space or large airspace required for safe flight. The ease of responding quickly to simple surveys for minor land readjustments or indoor work is a major advantage.

• Urban sites: On construction sites in urban areas, drone flights are accompanied by strict constraints. Obtaining flight permission in densely populated areas, considering privacy, and radio interference from surrounding buildings are often high hurdles. Because LRTK performs measurements from the ground, it is not affected by such aviation law restrictions and can acquire 3D data. In practice, in urban road construction sites where drone-based as-built measurement had been abandoned, the introduction of LRTK has enabled routine point cloud recording.

• Indoor and underground spaces: In indoor work or tunnels and underground structures, drones cannot fly properly because GPS does not reach. However, LRTK can utilize smartphone AR technology and various sensors to perform relative positioning and 3D scanning even in environments where satellite signals do not reach. In building interiors for piping and equipment installation work, LRTK can be used to scan the interior and help confirm as-built conditions. Indoor construction management, which was previously done by manually measuring dimensions and comparing them with drawings, can be greatly streamlined with LRTK.

• Disaster and emergency sites: Speed is required to grasp the situation immediately after disasters such as earthquakes and landslides. Drones are useful but may not be deployable if the weather is unstable or if the area is a no-fly zone. With LRTK, personnel can go to the site and start measuring immediately even in such emergencies. It can operate standalone when communication infrastructure is down, allowing quick surveying of evacuation shelters or provisional road locations. With high mobility and responsiveness, LRTK is a strong tool for disaster response and incident site recording. In fact, some local governments have reported cases where they used LRTK to record 3D data of landslide damage and used it to develop restoration plans.

Benefits of introducing LRTK: one-person surveying, rapid response, and labor reduction

Introducing LRTK on-site offers various benefits in terms of personnel and time. The following three points in particular will greatly contribute to improving productivity on construction sites:

• Realization of one-person surveying: With LRTK, surveying tasks that previously required multiple people can be completed by one person. For example, total station surveying required a two-person team of a surveyor and a staff member, but with LRTK the site person in charge can handle point cloud acquisition through drawing all by themselves. For small construction sites where it is difficult to allocate personnel or when surveying must be completed within limited working hours, LRTK enabling one-person operation is a powerful helper.

• Rapid on-site response: The convenience of being able to measure immediately without taking out dedicated equipment or planning a drone flight is also attractive. LRTK is easy to carry and quick to set up, so it can respond on the spot to sudden measurement needs. Even when you want to measure something right away on site, you can start LRTK and the smartphone and complete point cloud acquisition in a few minutes. Survey results can be shared to the cloud immediately, speeding up information transfer between the site and the office.

• Labor reduction and cost savings: Because site staff can perform measurements themselves without relying on skilled operators, outsourcing and personnel costs can be reduced. LRTK is easy to learn to operate, so training costs are minimal. In an industry suffering from severe labor shortages, the impact of LRTK enabling small teams to manage sites is significant. Furthermore, because it can handle everything from data acquisition to analysis in one workflow, tasks that were previously separate can be consolidated for greater efficiency, contributing to overall cost reductions.

LRTK accelerating on-site DX and its impact on the construction industry

Easy-to-use, high-precision 3D technologies like LRTK strongly support the DX (digital transformation) of construction sites. Because 3D surveying and construction management, which had been limited to some large-scale projects and specialized contractors, can be utilized routinely by more sites, productivity improvements across the industry are expected. In fact, combined with trends such as i-Construction and BIM/CIM promoted by the Ministry of Land, Infrastructure, Transport and Tourism, the use of digital data on sites is now an inevitable trend. LRTK has the potential to support on-site DX widely, from large enterprises to small and medium construction companies, as a tool that is easy to introduce.

Advancing on-site DX will improve operational efficiency and safety, and also positively affect working styles in the construction industry. For example, if laborious surveying tasks are digitized and streamlined, technicians can spend more time on higher value-added tasks. In addition, smart sites that actively use the latest technologies can be attractive to younger generations, aiding in securing human resources. If the spread of LRTK makes "3D construction" commonplace on sites, it will promote digitization across the construction industry and is expected to contribute to strengthening future international competitiveness.

Conclusion: Easily start next-generation 3D construction with LRTK

The wave of 3D construction driven by ICT technologies such as drones is about to broaden further with the emergence of LRTK. In situations where drone surveying was difficult, LRTK enables anyone to acquire 3D data through simple surveying and utilize that information on-site. Because LRTK can be started simply by attaching a device to a handheld smartphone without specialized equipment or large investments, the barriers to on-site introduction are low.

From sites that have actually introduced LRTK come feedback such as "we can get the data we need in a short time" and "waiting time for surveying has decreased, giving us more leeway in the schedule." It may be a good idea to try it on a small task first to experience the convenience. LRTK is a reliable on-site partner that realistically supports the promotion of on-site DX. Rather than relying solely on drone surveying, why not take on next-generation 3D construction using LRTK?