Streamlining Benchmark Point Searches Under Snow with Smartphones – DX for Winter Sites Using LRTK

Table of contents

• The problem of benchmark points being invisible in winter

• Traditional measures and limitations for confirming benchmark points in snow

• What is coordinate guidance with RTK? Easy positioning using smartphones

• Navigating "invisible benchmark points" with smartphones + RTK

• Innovating fieldwork by linking design data and using AR

• Winter site DX realized by introducing LRTK

• FAQ

The problem of benchmark points being invisible in winter

In winter construction and infrastructure sites, teams often struggle with benchmark points that are buried and not visible under snow. Survey control points and survey stakes installed for works can be hidden beneath the snow, making it difficult to identify their locations. As a result, surveying and inspection tasks during the snowy season do not proceed smoothly, and on-site productivity declines.

In heavy snowfall areas, for example, crews sometimes start work by digging through snow to search for benchmark points. Stakes that were carefully installed in advance cannot be seen under deep snow, and simply guessing where to dig can be a major ordeal. In some cases, precision-required surveys such as boundary confirmation must be postponed until the snow melts. Thus, confirming the positions of benchmark points and stakes under snow has long been a significant challenge for winter site workers.

Traditional measures and limitations for confirming benchmark points in snow

To address the problem of benchmark points being buried in snow during winter, several countermeasures have traditionally been used on sites. Representative methods and their challenges are as follows.

• Snow removal search: Estimate where the benchmark point is roughly located and remove snow over a wide area around it to find the stake. While reliable, extensive snow shoveling is hard physical labor, time-consuming, and places a large burden on personnel and costs.

• Extended markers: Attach long poles or flags to stakes or benchmarks so the markers remain visible above the snow. This can be effective to some extent, but it becomes meaningless if the markers are buried by heavy snow or blown down by wind and snow; if fully buried, the search effort is still required.

• Resurveying with surveying instruments: Determine the coordinates of a snow-buried benchmark by measuring from other known points. If a surveyor uses a total station to re-measure distances and angles from other visible points, the buried location can theoretically be pinpointed. However, this requires advanced surveying skills and multiple personnel; it is difficult if specialized technicians are not on site or staffing is limited.

• Postponing work: A common choice is to delay on-site work until spring rather than force surveys in the snow. Especially for precision tasks like boundary confirmation, the option “don’t do it while there’s snow” is sometimes taken. However, this stops construction and investigation during winter, leading to schedule losses.

Each of these measures has limitations. Wide-area snow removal requires manpower and time, increasing work costs and causing schedule delays. Working on snow worsens footing and raises safety risks. Relying on specialized surveyors is difficult amid labor shortages and busy sites. Consequently, surveying and inspection during the snow season have long been tasks that teams preferred to avoid when possible.

What is coordinate guidance with RTK? Easy positioning using smartphones

Recently, coordinate guidance using RTK has attracted attention as a technology to solve the winter benchmark search problem. RTK stands for Real Time Kinematic, a technique that achieves centimeter-class high-precision positioning by correcting GNSS errors in real time. Traditionally, RTK positioning required expensive dedicated GPS equipment and skilled operators, but now RTK can be conveniently used with smartphones.

In short, coordinate guidance with RTK means “navigating to coordinates.” If you already have the target point’s coordinates (latitude/longitude, etc.), an RTK-capable receiver can measure the current position with high precision and guide the user to that target coordinate. For example, in the past a surveyor would sight with a total station and guide an assistant on site, or measure distances from known points using a tape measure to set out a position; with RTK coordinate guidance, the device automatically navigates for you.

Specifically, an RTK survey is performed with a high-precision GNSS receiver attached to a smartphone (such as an LRTK device described later), and the target coordinates are specified in a dedicated app. The smartphone screen then displays the direction and distance to the target in real time, and the user simply follows that guidance to reach the desired point. It functions like a car navigation app on a map, directing you to the construction benchmark. No complicated operation is required—workers holding a smartphone just walk in the direction the arrow points, and high-precision point searching or staking is completed.

An important point here is positioning accuracy. Built-in smartphone GPS typically has errors of several meters (several ft), making it difficult to find a single stake driven into the ground. But with an RTK-positioned smartphone, the error is within a few centimeters (within a few inches). In other words, “navigation with only a few centimeters (a few inches) of deviation” becomes possible, allowing pinpoint discovery of small markers hidden under snow.

Navigating "invisible benchmark points" with smartphones + RTK

Let’s see how coordinate guidance combining a smartphone and RTK actually performs in searching for benchmark points that are invisible due to snow. An easy-to-imagine case is locating survey stakes or boundary markers installed before winter, after snowfall. Traditionally, one had to dig broadly while guessing where a buried stake might be, but with a smartphone + RTK setup, that effort can be drastically reduced.

For example, if the exact coordinate data of a buried stake is known in advance, a worker inputs that coordinate into a smartphone app. The stake’s location is then marked on the smartphone screen, with direction and distance from the current position displayed. The worker walks in the arrow’s direction until the distance reads zero—that is, until they are directly above the stake. Even if the area is entirely covered in snow, the system guides the user to the very spot above a stake that has no visible marker, eliminating the need to search over a wide area. All that’s typically required is brushing a little snow off the immediate point to confirm the stake head.

Using smartphone-based coordinate guidance can dramatically improve efficiency in “finding benchmark points hidden by snow.” Field reports have shown cases where boundary stakes buried by vegetation or benchmarks hidden by snow were found in a short time using AR markers on the smartphone screen. Because no complex instrument operation is needed, even less-experienced workers can intuitively use the system and locate target points to centimeter-class accuracy. Tasks that used to wait for a surveyor—stake finding and position setting—can now be handled by on-site personnel themselves, reducing wait times and staffing needs.

Moreover, this smartphone + RTK navigation is useful not only for staking and verification during construction, but also for fixed-point observation and equipment inspection. For instance, for positioning foundation pile centers, importing the pile center coordinates from design drawings into the app and using guidance lets a single person accurately mark pile-driving positions. This reduces the need for traditional batter boards and chalk lines, speeding up construction. For periodic inspections of infrastructure, having previously registered inspection point coordinates ensures that even if those points are buried under snow on repeat visits, you can reliably return to the same spot. Performing measurements and observations consistently at identical points improves monitoring and comparisons over time. Thus, smartphone + RTK use opens new possibilities for winter surveying and inspection work.

Innovating fieldwork by linking design data and using AR

The strength of a smartphone + RTK solution is not limited to coordinate guidance alone. By linking with pre-existing design data and drawings, the available digital functions on site expand further.

If you load reference point coordinates from construction drawings or design layout data into the dedicated app beforehand, you can quickly call up and display positions you need to check on site. For example, selecting a menu item like “△△ benchmark” or “position specified in the design” will plot that point on the smartphone map. This alone reduces the need to constantly compare paper drawings with current location, but even more powerful is using AR (augmented reality) display.

AR overlays benchmark points and design lines on the smartphone camera feed so that invisible elements become “visible” on site. For example, you can show the locations of buried pipes or handholes beneath snow as AR markers, or virtually display the centerline of a road or the outlines of structures from the design on the ground. Even in snowfields, pointing the smartphone will make invisible benchmarks and lines appear, allowing intuitive grasp of spatial relationships. This can help prevent accidental digging into underground pipes or enable stakeholders to accurately share boundary lines.

Photo documentation is another benefit for site DX. When taking site photos with a smartphone, you can simultaneously record high-precision shooting coordinates from RTK positioning and camera orientation (bearing) information. While conventional smartphone photos can include geotags, their error of several meters (several ft) is too coarse for construction records. A system combined with high-precision GNSS can record exactly where each photo was taken to within a few centimeters (within a few inches), making the photos far more reliable as data. For example, when inspecting structures after heavy snowfall and photographing damaged areas, you can later precisely trace where the photos were taken on site, aiding repair planning.

Furthermore, positioning data and recorded photos obtained on site can be shared instantly via cloud synchronization. With a tap on the smartphone, recorded point information and photos upload to the cloud and can be checked in real time from office PCs. This lets on-site staff and remote supervisors always share the latest information, enabling speedy instructions and decisions. There’s no need to jot notes in paper fieldbooks and bring them back; data is automatically centralized and managed. Results from different surveyors can be consolidated in the cloud for efficient report creation and as-built management. This truly promotes digitalization and real-time workflows on site, reducing errors and speeding information sharing.

Winter site DX realized by introducing LRTK

The above technologies are embodied on actual sites by our solution called LRTK. LRTK consists of a compact RTK-GNSS receiver that can be attached to a smartphone, a dedicated app, and cloud services, enabling simple surveying with a smartphone. The device fits in your pocket and attaches to a smartphone with a single touch, allowing anyone to start centimeter-class surveying right away.

Introducing LRTK to winter sites transforms surveying and inspection tasks that used to be difficult due to snow. A single person can handle everything from verifying benchmark coordinates to staking, reducing the need to arrange large surveying crews in winter. There’s no need to carry heavy surveying equipment through snowy roads; you can measure and record whenever needed. With coordinate guidance usable even under snow, large-scale snow removal done solely for surveying can be greatly reduced. Shorter work times lower exposure to harsh weather and improve safety.

Establishing a digital surveying workflow with LRTK dramatically raises site productivity and quality. Data acquired can be shared to the cloud on the spot for immediate communication with stakeholders, enabling real-time remote instructions and verification. Because a certain level of accuracy can be ensured without relying on highly experienced surveyors, limited skilled personnel can be utilized more effectively across multiple sites. This also aligns with national initiatives such as *i-Construction* and *ICT施工*, demonstrating that adopting the latest technologies contributes to DX-driven competitiveness and external appeal for companies.

Work that traditionally stalled in winter can now run stably year-round by incorporating simple surveying with LRTK. More sites are overcoming the handicap of snowfall with digital technology, achieving efficiency and labor savings. Use this new tool that is reshaping winter surveying styles and advance DX of surveying and inspection at your sites.

FAQ

Q: Why is LRTK so much more accurate than a smartphone's GPS? A: LRTK performs real-time error corrections on satellite signals received by a high-precision GNSS receiver. Specifically, it uses correction data distributed from nearby reference stations (or the CLAS signal from Japan’s Quasi-Zenith Satellite System “Michibiki”) to cancel out GNSS error factors. As a result, errors that were several meters (several ft) with a smartphone alone are reduced to about 1–2 cm (0.4–0.8 in), achieving surveying-instrument-level accuracy.

Q: Can people with little surveying experience operate it? A: Yes. LRTK is designed to be easy to use without specialized knowledge. Basic operations are completed by tapping buttons in the smartphone app, and AR displays are intuitive. If you have used map apps before, you'll quickly get the hang of it. Advanced surveying calculations or complex settings are unnecessary; follow the guidance and anyone can perform high-precision positioning. Basic knowledge of coordinates helps, and manufacturer manuals and support are available for reassurance.

Q: Can LRTK be used at sites with no cellular coverage, such as mountainous areas? A: Yes. LRTK can be used without a communication environment. In places where RTK correction data cannot be received over the Internet, you can use the centimeter-class augmentation service (CLAS) provided by Japan’s Quasi-Zenith Satellite “Michibiki.” Supported LRTK receiver models can receive CLAS signals directly, enabling centimeter-class positioning even outside cell coverage. However, positioning is naturally difficult inside tunnels or underground where satellite signals cannot reach (in such cases the LRTK app’s indoor mode can estimate position relative to reference points at locations where satellites are visible).

Q: I'm worried the equipment might fail in cold regions or under snowfall. Is durability sufficient? A: LRTK receivers are designed with waterproof and dustproof specifications for field use and operate reliably in snow and rain. Their operational temperature range supports extremely cold environments, and stable operation has already been confirmed in severe winter field tests. Battery performance does drop somewhat in low temperatures, so continuous operation time decreases, but the device is designed to provide about 7 hours of continuous positioning around -20℃. This is sufficient for typical tasks, and using a spare mobile battery allows all-day surveying. With proper battery management and cold-weather precautions, even in extreme cold you can use it with confidence.

Q: Which smartphones are supported and what equipment should we prepare? A: The LRTK system currently supports smart devices running iOS (smartphones and tablets). Newer models with higher camera and sensor performance make AR features and point-cloud scanning more comfortable to use (for example, devices with LiDAR scanners can perform advanced 3D measurements). The necessary equipment is just the compact LRTK receiver and a smartphone. The receiver attaches to the smartphone with a dedicated attachment and has an integrated antenna and battery, so no external power or messy wiring is required. No special installation is necessary—take it out on site and start measuring immediately.