Graduate from paper drawings! Smart reverse construction with LRTK's AR coordinate navigation

Construction managers and surveyors performing "reverse construction" (saka-uchi), are you still chasing coordinates on site with paper drawings in hand? Relying on paper drawings for layout work involves many laborious steps and carries the risk that small errors can lead to major rework. What deserves attention is LRTK's AR coordinate navigation, which uses a smartphone and RTK technology. With LRTK, you can intuitively guide to design coordinates via AR display, graduate from paper drawings, and simultaneously achieve efficiency, improved accuracy, and enhanced safety. This article explains the reverse construction method, the problems of conventional methods, and the concrete benefits of smart reverse construction using LRTK.

What is reverse construction?

First, let’s briefly review what the reverse construction method (saka-uchi) is. Reverse construction is a specialized technique used in constructing buildings with underground floors. Normally, the underground portion is excavated and constructed upward from the foundations, but reverse construction is characterized by constructing the underground structure from the top down. Specifically, the ground-level portion or the first-floor slab is built first, and then excavation and underground construction proceed sequentially using that slab as support. Because the sequence is the reverse of the usual method, it is called "reverse construction" and has been used since the 1960s in urban building projects.

The advantages of reverse construction are shortened construction periods and improved safety. Because above-ground and underground work can proceed in parallel, significant time savings are possible; the first-floor slab acts as a cover to reduce noise and dust while functioning as temporary support to safely allow underground excavation. On the other hand, disadvantages include cramped working spaces underground and difficulty in integrating upper and lower structures later. Therefore, in reverse construction, how accurately surveying and layout can be performed in limited space becomes a crucial point. Since the ground slab is built first, the reverse layout work—precisely locating underground columns and walls afterward—requires advanced surveying control.

Conventional reverse construction work and the issues of relying on paper drawings

Not only in reverse construction but across construction sites, layout work based on design drawing coordinates (marking layout lines or stake positions) has long relied on human effort. Traditionally, construction managers or surveyors read coordinate values written on paper drawings, used tape measures or total stations to determine survey points on site, and marked positions on the ground or structures. However, this analog method has the following issues.

• Difficulty surveying in confined spaces: In reverse construction, underground workspaces are tight, and performing conventional surveying with a ceiling (upper floor slab) in place is not easy. Poor lines of sight and restrictions on equipment setup make layout work time-consuming.

• Inefficiency due to multi-person tasks: Stake layout using surveying equipment generally requires teams of at least two people. One holds a staff rod while another operates the instrument, increasing manpower and labor hours.

• Reading errors from paper drawings: Careless mistakes when transcribing coordinate values from drawings or misreading dimensions on site can lead to human errors. Especially when dealing with complex coordinates or numbers with many digits, small mistakes can cause position offsets.

• Marking mistakes and rework: Manual layout marking can result in marks placed in the wrong position. If discrepancies are discovered after construction, major rework like recasting concrete or reinstalling structural elements may be required, severely impacting schedule and cost.

• Safety risks: Surveying sometimes requires workers to enter dangerous areas near heavy machinery or below slopes. Reverse construction increases work inside underground pits, raising concerns about falling objects from above or slips and falls, complicating safety management.

As shown above, layout work for reverse construction based on paper drawings and manual processes has limits in both efficiency and accuracy and also affects site safety. Executing work "exactly as the drawings show" is a highly challenging task. So how can these issues be solved? The answer is the digital reverse construction enabled by LRTK's AR coordinate navigation.

What is LRTK's AR coordinate navigation?

LRTK is a next-generation positioning system developed by Refyxia Co., Ltd., consisting of a compact RTK-GNSS receiver that attaches to a smartphone. Combined with a dedicated app, it enables centimeter-level high-precision positioning and coordinate guidance via AR (augmented reality). The AR coordinate navigation function of LRTK makes precise layout work—previously requiring specialized surveying equipment and expertise—intuitive and doable by anyone with just a smartphone. Let’s look at its mechanisms and features.

Centimeter-level positioning using RTK technology

LRTK’s main feature is its use of RTK (Real Time Kinematic) technology in GNSS positioning, which keeps positioning errors within a few centimeters. Ordinary GPS positioning can have errors of several meters (several ft), but RTK greatly improves accuracy by applying real-time differential corrections between a base station and a rover. LRTK receives RTK correction information over the internet, allowing a smartphone to constantly obtain highly accurate current coordinates. For example, in an open outdoor environment, starting LRTK typically achieves an RTK "Fix" in about 30 seconds, providing horizontal position accuracy of about ±1-2 cm (±0.4-0.8 in). This effectively eliminates the discrepancy between the design coordinates on drawings and your measured on-site position, enabling layout with a level of accuracy incomparable to pulling a tape measure while looking at paper drawings.

Supported by high-precision RTK positioning, LRTK’s coordinate navigation enables guidance that “does not drift.” Because it continuously compares your GNSS-measured current position against the target coordinates, it is more reliable than traditional methods like extending a tape measure from a survey point by a specified number of meters. Capturing column positions and alignment points critical to reverse construction with RTK centimeter accuracy prevents misalignments in the structure and greatly reduces the risk of accuracy-related defects in later work.

Intuitive position guidance with AR display

What sets LRTK apart from other positioning systems is its AR display-based coordinate guidance. By showing target positions visually through the smartphone screen, it guides users intuitively to the correct spot without requiring expert skill. Specifically, when you select a target coordinate in the LRTK app, the screen displays arrows and distances in real time, guiding you with instructions like “12 cm east” or “8 cm north.” The worker simply follows the arrow on the smartphone toward the target, and when the distance readout approaches zero, they have reached the desired coordinate. Tasks that previously required a surveyor to measure and direct can now be completed simply by following the smartphone display.

Moreover, when you approach the target point, a virtual stake (AR stake) or marker appears on the screen, making it look as if a stake is actually standing at that location. Because the AR marker clearly shows “this is the point specified in the design,” you only need to drive a real stake or mark that position. Virtual objects superimposed on the surrounding scene prevent losing sight of the target even at night or in poor visibility—just look at the smartphone screen. AR transforms the abstract task of calculating a point on paper and transposing it to the ground into the concrete action of “seeing it directly in the real space” — this is the innovation LRTK’s AR coordinate navigation brings to the field.

Easy operation using a smartphone

LRTK runs on smartphones and tablets, so its usability is no different from the apps you use every day. No large dedicated equipment or special skills are required; the user interface is intuitive for anyone on site. For example, press the “Navigate” button in the app to start guidance, and press “Record” when you arrive to save the coordinate—simple button operations let you complete everything from surveying to stake guidance. As a smartphone feature, if you take on-site photos during guidance, the position coordinates and orientation are automatically recorded, making it easy to later review “where that stake was placed.”

The device itself is pocket-sized and lightweight, so workers can carry it at all times and use it immediately when needed. You simply attach a GNSS receiver weighing only a few hundred grams to your smartphone; with an optional monopod you can easily adjust height offsets. Even in situations that used to require carrying heavy tripods, with LRTK you can move around site with a smartphone in one hand and a notepad in the other. The fact that one device per person is realistic in terms of price and size is significant: it enables a workflow shift from “surveying is the task of a specialist team” to “each responsible person can perform positioning and layout themselves.” This directly improves overall site productivity.

Real-time sharing via cloud integration

LRTK’s integration with cloud services is also noteworthy. If you upload design drawings and coordinate data lists to the LRTK cloud beforehand, the site smartphone apps can synchronize and immediately use that data for guidance. This means you no longer need to carry paper drawings or coordinate tables—you can call up the latest design coordinates on site at any time. If drawings are revised, updating data in the cloud instantly reflects the change on everyone’s devices, preventing mistakes like “we were working from an old drawing.”

Furthermore, positioning and recorded on-site information can be uploaded to the cloud with a single button, enabling real-time data sharing with office staff. If you send coordinates and photos of staked points to the cloud from site, the office can immediately verify the as-built condition or reflect it in record drawings. Time-consuming tasks like organizing survey data and preparing reports become efficient since the cloud can automatically convert coordinates and output drawings. In short, LRTK connects the field and the office seamlessly, allowing you to move away from analog management reliant on paper drawings and handwritten notes. With centralized data management and everyone sharing the same information, ensuring construction quality and managing progress on site becomes much easier.

Efficiency, accuracy, and safety improvements realized by smart reverse construction

As described above, LRTK’s AR coordinate navigation greatly transforms reverse construction workflows. What specific effects can be achieved? Below is a summary from the perspectives of work efficiency, surveying accuracy, and safety.

Work efficiency: large reductions in manpower and time

One of the biggest benefits of adopting digital guidance is the reduction and acceleration of surveying and layout tasks. Because LRTK’s coordinate guidance can be operated by a single person, the multi-person surveying that was previously necessary becomes unnecessary. This alone improves personnel allocation efficiency and reduces labor costs, and because each person can simultaneously survey and stake different points, the overall site speed increases. For example, at one site using a GNSS + AR staking system, the time required to set out survey points was reported to be reduced to about one-sixth compared with traditional optical surveying. Because you can produce stake positions simply by moving while looking at the device, the number of points processed per day dramatically increases, leading to shorter schedules and lowered costs.

Reducing rework also contributes to efficiency improvements. High guidance accuracy dramatically reduces redo work due to position offsets, enabling correct construction on the first attempt. Previously, when marking mistakes were discovered, re-surveying and rework could consume half a day; with LRTK you can stake or mark the intended position correctly the first time, eliminating waste. Eliminating the need to spread out paper drawings and measure here and there also reduces associated setup time (moving between survey points, recording survey results by hand, etc.), yielding dramatic productivity improvements overall.

Positioning accuracy: eliminate errors and improve construction quality

Improved accuracy is critical in reverse construction. The combination of RTK centimeter accuracy and AR guidance virtually eliminates coordinate deviations caused by human error or measurement mistakes. This directly stabilizes construction quality. In reverse construction of underground structures, even a few centimeters of misalignment in columns or beams can affect connections with the above structure. By performing precise layout with LRTK, the whole structure’s dimensional accuracy can be maintained at a high level, preventing adjustment work or defects in later stages.

Also, the reassurance of consistently high accuracy reduces stress on site. Previously, workers often double- or triple-checked positions or sought expert surveyor input to be sure everything was correct. LRTK’s screen displays numerical and visual offsets between the current position and the target coordinate, allowing anyone to objectively grasp accuracy. As a result, variability in construction accuracy is reduced, and even without relying on veterans, uniform quality in layout and staking can be achieved. Making high-precision alignment the norm eliminates human errors like “it drifted by a few centimeters without noticing,” contributing to higher pass rates in quality inspections and fewer quality defects.

Safety: reducing hazardous tasks and preventing human error

Manual reverse layout relying on paper drawings had room for safety improvements. Smart reverse construction with LRTK also enhances worksite safety. First, reducing the time required for surveying and staking shortens the time workers spend in hazardous areas. Minimizing time spent in areas with operating heavy equipment or deep excavations reduces risk. The ability to work with fewer people is also important. Where surveying previously required multiple people moving across the site, LRTK allows minimal staffing, reducing risks of contact incidents and human errors.

Furthermore, AR technology enables hazard avoidance. For example, in locations where humans cannot physically enter—steep slopes or areas with hard concrete floors where stakes cannot be driven—LRTK’s AR function lets you place virtual stakes from a safe location to confirm positions. Increasing situations where you can perform positioning and marking remotely eliminates the need for risky approximations like “we couldn’t get close, so we eyeballed the position.” Also, because you no longer need to look down at paper drawings on site and can keep your head up to follow the screen guidance, the chance of losing situational awareness is reduced. Being able to confirm guidance on the screen while facing forward makes it easier to maintain both safety checks and work progress even on uneven ground.

In terms of preventing human error, safety and quality are two sides of the same coin. Digital guidance prevents mistakes from incorrect assumptions or missed observations due to fatigue, helping nip potential accidents in the bud. LRTK is a technology that supports on-site peace of mind and safety.

Conclusion: Achieve paperless smart reverse construction with LRTK

Even for advanced construction methods like reverse construction, the era of relying only on paper drawings and tape measures is over. By using LRTK’s AR coordinate navigation, anyone can perform centimeter-level layout with a smartphone, progressing reverse construction efficiently and with high accuracy. Digital solutions eliminate the labor and mistakes that plagued conventional methods, greatly improving on-site productivity and safety. This goes beyond merely introducing a convenient gadget; it aligns with industry-wide DX (digital transformation) and i-Construction initiatives promoted across the construction sector.

To move beyond paper drawings and elevate on-site surveying and construction management to the next stage, LRTK is a powerful partner. Once you try it, its intuitive guidance and reliable accuracy will surely surprise you. Cumbersome reverse construction surveys become smart, reducing the burden on construction managers and surveyors. Please consider introducing this new smart reverse construction approach to your site. Say goodbye to paper drawings with the power of LRTK and shift your site into a new era of efficiency and high-precision construction.