Complete land improvement surveying with only a smartphone! Eliminate outsourcing with the ultra-compact GNSS terminal LRTK

Importance of surveying work in land improvement projects and the challenges of outsourcing

In land improvement projects (in the field of agricultural civil engineering), work is carried out to enhance the foundation of agricultural production, such as farmland development and the construction of water control facilities. Surveying is an indispensable and continuous task in these projects, from planning and design through construction and post-completion verification. By accurately grasping terrain data and positional information, appropriate designs can be made, directly preventing construction errors and enabling quality control. However, in many cases these surveying tasks are outsourced to external surveyors or specialized contractors, which creates various challenges.

Typically, land improvement associations and local governments lack in-house surveying specialists, so they must commission licensed surveyors or contractors equipped with the latest instruments. Relying on outsourcing, however, hides issues that cannot be ignored on site, such as increased costs, the hassle of scheduling, and time losses associated with transferring survey results.

On-site burdens related to surveying (manpower, cost, scheduling, re-surveying)

When surveying is outsourced, many burdens fall on on-site technicians.

• Human resources: Dependence on specialists such as surveyors prevents in-house accumulation of know-how, and site personnel need to attend surveys, taking time away from their usual duties.

• Cost: Outsourcing fees to surveying companies strain budgets. Even for small-scale improvement works or additional surveys due to design changes, outsourcing costs arise, often resulting in a heavy expense burden.

• Scheduling difficulties: When survey dates must be changed due to bad weather or coordination with farmers, rescheduling with external contractors tends to be complicated.

• Risk of re-surveying: If design changes or errors are discovered after surveying and re-surveying is required, each instance incurs the inconvenience and cost of calling in professionals, which can lead to construction delays.

Basics of GNSS surveying and the advantages of RTK technology

Surveying methods have evolved significantly in recent years. One such advancement is GNSS surveying (positioning using global navigation satellite systems). GNSS, which receives signals from satellites to determine position coordinates, differs from traditional transit or total station methods that measure relative angles and distances; it allows a single person to quickly obtain positions over large fields or long waterways. As long as there are no obstructions, there is no limit to the line-of-sight distance, enabling efficient surveying of multiple distant points, and its use in land improvement sites is steadily increasing.

However, ordinary GNSS (standalone positioning) produces errors on the order of several meters, making it unsuitable for detailed civil engineering surveys. RTK (Real Time Kinematic) technology addresses this. RTK uses two receivers—a base station (reference) and a rover—that communicate in real time to correct GNSS error sources and achieve centimeter-level accuracy. In Japan, with the availability of the Geospatial Information Authority’s electronic reference point network and the quasi-zenith satellite Michibiki (services like CLAS), high-precision correction information can be obtained without setting up your own base station. The advantage of GNSS surveying with RTK is that it provides high-precision 3D positions in a short time. From wide-area topographic surveys to pinpoint elevation checks, results can be obtained in real time, streamlining tasks that previously required multiple personnel and greatly reducing the number of days spent on surveying.

That said, until now, using RTK surveying required dedicated equipment costing several million yen and complex setup work, making it impractical for ordinary technicians. A solution that dramatically lowers these barriers and is attracting attention is a new approach called LRTK, which combines a smartphone with an ultra-compact GNSS terminal.

How LRTK (smartphone × small GNSS) works and its operability

LRTK is an innovative system that transforms a smartphone into an all-purpose surveying device capable of centimeter-level positioning. Developed by a startup originating from the Tokyo Institute of Technology, this system is designed to reflect the needs of Japanese fieldwork. A dedicated ultra-compact RTK-GNSS receiver (terminal) that attaches to iPhones or Android smartphones is used together with a dedicated app that links to the phone’s camera and LiDAR sensor. The receiver weighs only about 150 g, and its thickness is around 1 cm (0.4 in), making it thin and lightweight so it does not add bulk when attached to a smartphone and is easy to carry. It runs on an internal battery and connects wirelessly to the phone, so no cables are necessary.

Actual operation is simple. After attaching the LRTK device to a smartphone and powering it on, correction information via the internet is automatically applied to the GNSS satellite signals, and positioning accuracy improves noticeably within seconds. In open areas, RTK typically achieves a FIX solution (transitioning from float to fixed) in about 30 seconds to 1 minute, enabling high-precision positioning with an error of only about ±2 cm (±0.8 in). The positioning status can always be checked on the app screen, which displays statuses such as "no RTK" (accuracy ± several meters), "Float" (about ±1 m (±3.3 ft)), and "Fix" (within ±2 cm (±0.8 in)). Once high precision is established, the user simply records the points to be measured on site or walks around to scan, following the smartphone screen prompts.

With a single LRTK device, everything from recording position coordinates to obtaining high-precision point cloud data, guiding stake-out positions based on design drawings (layout), and verifying as-built conditions via AR overlays on camera images can be completed using only a smartphone. Heavy tripods and complex setups are unnecessary, and even young technicians without specialized surveying knowledge can operate it intuitively. Tasks that used to be requested of surveying teams can now be performed by site personnel at their convenience, making a next-generation surveying style—“anyone can survey alone”—a reality.

Specific use cases (field consolidation, waterways/drainage channels, farm roads, reservoirs, boundary verification)

Field consolidation (field parcel reorganization and ground leveling)

In field consolidation, irregular paddy field parcels are enlarged and leveled with a uniform slope to improve agricultural work efficiency. This requires thorough surveying for grasping current elevation differences, calculating cut-and-fill volumes, and post-construction elevation checks.

Traditionally, plane-table surveys or levels were used to measure ground elevations at many points to create topographic maps.

With LRTK, a single person can walk through a paddy field and easily obtain elevation points over a wide area. Since the measured elevation data distribution can be visualized on the smartphone screen in real time, overall trends in elevation differences can be grasped immediately.

For example, you can scan parcel ground surfaces into point clouds and automatically calculate the required earthwork quantities on site.

During construction, you can confirm in real time how many centimeters of fill are still needed to reach the design surface, and after completion you can re-scan to immediately check whether the as-built matches the plan. Being able to internalize the series of surveying and as-built verification tasks associated with field consolidation without repeatedly calling in a surveying company is a major benefit.

Surveying and design of irrigation and drainage channels

LRTK is also powerful for the construction or improvement of agricultural irrigation and drainage channels. Longitudinal surveys along endless waterways can be performed efficiently by walking with a smartphone equipped with the receiver, continuously collecting elevation data to investigate line gradients.

Elevation points collected on site are automatically converted to sea level elevations with centimeter-level precision, eliminating the need for coordinate conversions in the office.

You can check the elevation difference between the upstream and downstream on the spot, compare it to the planned gradient, and calculate the necessary earthwork volumes.

If you take photos with the camera on site, you can link photos and notes to each surveyed point, enabling centralized cloud management of annotations such as "this point has a field crossing culvert" or "this area has soft ground" when creating design drawings later.

During construction, you can continuously verify with LRTK whether the gradient matches the design and quickly correct under- or over-excavation. For long drainage and irrigation channels, digital surveying with LRTK allows denser point intervals, reducing the need for additional surveys later.

Layout planning and stake-out for farm roads

In constructing farm roads and access roads, aligning route geometry (curves and slopes) with the actual terrain is important.

Traditionally, route surveying involved setting batter boards from the start point to the end point while surveying, but with LRTK you can perform surveying and design evaluation simultaneously.

For example, by walking along candidate routes and measuring with LRTK, distance and elevation data are obtained in real time, allowing you to grasp longitudinal and cross-sectional images on the screen.

You can compare multiple route options in a short time and immediately share the results in the cloud to discuss with stakeholders.

LRTK is also powerful for stake-out work after design is finalized. Based on pre-configured design alignment coordinates, the smartphone guides workers with directions like "50 cm east to go" and "height +5 cm to go," enabling a single worker to accurately perform batter board setup and elevation control that previously required a team of a surveyor and a helper. When approaching the stake position, AR marking appears, allowing pinpoint placement without relying on feel, and complex positioning at curves or intersections can be done without errors.

Reservoir maintenance and slope measurement

LRTK is useful for the renovation and inspection of agricultural reservoirs. By measuring the 3D shapes of embankments and pond bottoms, you can accurately grasp changes in storage capacity and any deformation.

Traditionally, teams walked around the pond measuring representative cross-sections of slopes or floated a GPS-equipped boat to measure water depths.

Using LRTK, a single person can quickly acquire point cloud data in a short time during periods when the pond is drained. LiDAR scanning on the smartphone combined with GNSS position correction records wide-area slopes accurately and without distortion as high-precision point clouds.

From the obtained data, you can calculate current soil volumes to instantly identify the amount of deposited sediment and the areas that need dredging.

In emergency surveys after slope failures caused by heavy rain, scanning the collapse from a safe location without entering dangerous slopes reduces the risk of secondary disasters. Overlaying the acquired point cloud with past drawings or design models allows you to quantify which parts have been eroded or subsided and by how much, providing useful material for repair planning.

Boundary confirmation and boundary meetings

Land improvement projects involve boundary confirmation and on-site boundary meetings with adjacent landowners as part of land readjustment.

Using LRTK, you can guide stake-out to boundary point coordinates set on the design drawings and place boundary markers at accurate positions on site.

During meetings with farmers or landowners, displaying aerial photos or topographic maps on the smartphone while showing your current position and boundary lines makes explanations visually easy to understand.

Unlike simple methods with large survey errors (measuring tape or visual estimation), GNSS-based objective evidence gives stakeholders confidence in confirming boundaries.

If you save LRTK positioning records and site photos at each boundary point in the cloud, you can later share evidence such as "the boundary between Parcel A and Parcel B is at this point" in case of disputes, smoothing the consensus-building process. Being able to perform boundary confirmation in-house to a certain level of accuracy without hiring a surveyor is a significant advantage for land improvement associations and local governments.

Workflow to internalize point cloud acquisition, as-built verification, and plan drafting

By introducing LRTK, you can handle the surveying, design, and as-built management processes of land improvement projects entirely in-house. The following is an example of that workflow.

• Current 3D surveying (point cloud acquisition): Before starting construction, use LRTK to measure the terrain of the target area in detail. Obtain point cloud data of fields and waterways using the smartphone’s LiDAR scan and photogrammetry functions to create a current terrain model. While creating traditional survey or contour maps was time-consuming, point clouds can digitally record subtle surface undulations. Even if you later decide you need to survey another area, having point cloud data reduces the frequency of additional on-site surveys.

• Design and plan drafting: Based on the current data, design work is done in the office. Survey data uploaded to the LRTK cloud can be inspected in 3D or sliced for cross-sections in a browser, allowing designers to accurately understand the terrain when planning. If necessary, point cloud data can be imported into CAD software to smoothly create slope and channel longitudinal/cross sections and parcel maps. If questions arise during design, you can immediately supplement the data by conducting another LRTK survey in-house, avoiding time losses spent waiting for external contractors to respond.

• Stake-out and construction: The completed design plan can be imported into the LRTK app or cloud for on-site use. For example, LRTK can navigate stake-out positions based on design baselines and elevation information, enabling the construction team to set batter boards and control elevations themselves. Even on sites short of experienced personnel, following the smartphone guidance ensures the required alignments and elevations, preventing variability in construction quality.

• As-built verification (inspection survey): After construction is complete, perform as-built surveying again using LRTK. By overlaying the as-built point cloud with the design data in the cloud, you can immediately determine the success or failure of the as-built shape. If elevation is insufficient, the point cloud will appear lower than the design model; if there is excess, the point cloud will protrude—allowing quick completion of inspection cross-sections and quantity calculations. This streamlines the preparation of inspection documents and enables early submission of results to the client and relevant agencies.

• Drafting drawings and data sharing: All data acquired by LRTK is stored in the cloud, facilitating the drafting of final drawings. Processes such as drawing plans by connecting measured points or extracting necessary cross-section shapes from point clouds were previously manual, but in an LRTK environment they can be semi-automated digitally. Moreover, the organized surveying results in the cloud can be used directly as electronic deliverables or easily shared among stakeholders. Data-centric collaboration without relying on paper drawings allows you to fully leverage in-house surveying data to improve overall project productivity.

Effects on outsourcing cost reduction, response improvement, and consensus-building with farmers

• Cost reduction: By internalizing surveying tasks, you can significantly reduce outsourcing fees. Although initial investment is required to introduce LRTK, repeated in-house surveying by your own staff yields high cost benefits in the long term. Especially for small improvements or prompt responses to design changes without incurring additional costs, LRTK is advantageous for budget management.

• Improved responsiveness: Having the ability to measure whenever needed dramatically speeds up on-site decision-making. Waiting on a surveying company’s schedule is eliminated, preventing situations like “construction starts tomorrow but reference point surveying hasn’t been done.” If questions arise during design, you can verify the site and collect data the same day, accelerating the PDCA cycle. In disaster response, the immediate capability of in-house surveying demonstrates unique responsiveness.

• Effects on consensus-building: Explanations based on accurate survey data increase farmers’ and landowners’ confidence. During meetings, showing point cloud models or surveyed point information on aerial photos helps stakeholders share a concrete image of the completed work that was previously left to imagination. The objective fact of “we measured it properly” fosters trust, facilitating smoother compensation negotiations and land readjustment planning. Shortening the time required for consensus-building contributes to speeding up the entire project.

Conclusion: Consider introducing simplified surveying with LRTK

With labor shortages and work-style reforms in focus, improving the efficiency of surveying and internalizing it are increasingly important themes in agricultural civil engineering. The smartphone-only surveying introduced in this article is attracting attention as a solution that overturns conventional wisdom. Sites that have adopted LRTK are already seeing tangible effects such as reduced surveying costs, faster decision-making, and smoother consensus-building with stakeholders. Those involved in land improvement projects are encouraged to consider introducing simplified surveying with LRTK to innovate surveying operations on site. Such smartphone surveying initiatives also align with the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction and the Ministry of Agriculture, Forestry and Fisheries’ promotion policies for smart agriculture and ICT construction, and further diffusion is expected. Use the latest technology in smartphone surveying to dramatically enhance your land improvement site capabilities. Experience the benefits at your site.