RTK for Grading: Efficient Checking of Slopes and Elevation

Table of Contents

• What is RTK? Why high-precision positioning is necessary for grading and slope checks

• How introducing RTK changes grading work (labor savings and efficiency)

• How to efficiently check slope and elevation with RTK

• Points to watch when using RTK surveying

• Simple surveying with LRTK

• FAQ

In recent years, the construction industry has pushed DX (digital transformation), and site ICT such as *i-Construction* has advanced. In that context, RTK (Real-Time Kinematic) has attracted attention as a high-precision positioning technology. By introducing RTK, it is expected that surveying work can achieve dramatic improvements in efficiency (reduced work time and labor) and accuracy.

In particular, in grading and earthwork, it is extremely important to accurately check the finished slope and elevation (height). Even an error of a few centimeters (a few inches) can lead to inadequate drainage slope or surface irregularities, so it is necessary to rigorously inspect whether the finished ground elevation and slope match the design. Traditionally, these checks were performed carefully by multiple people using optical levels or total stations, but using RTK makes these tasks far more efficient.

This article explains the benefits, use cases, and differences from traditional methods for checking slopes and elevations on grading sites using RTK. At the end of the article, we also introduce a simple surveying solution, “LRTK,” which makes RTK adoption easy.

What is RTK? Why high-precision positioning is necessary for grading and slope checks

High positioning accuracy is required when leveling land or checking slopes on construction sites. For example, if the finished elevation is off by just a few centimeters (a few inches), it can lead to insufficient drainage slope or surface irregularities of pavement. Therefore, in earthworks and road construction, it is important to accurately measure and manage whether the finished ground elevation and slope match the design. However, conventional standalone GPS positioning can have errors of several meters (several ft), making it unsuitable for precise grading checks.

This is where RTK positioning comes in. RTK (Real Time Kinematic) operates two GNSS receivers simultaneously: a base station fixed at a known coordinate and a rover that moves while being positioned. The base station calculates errors from the satellite signals it receives and its known accurate position, then sends that correction data to the rover. The rover subtracts the error components from its position in real time, reducing the typical GNSS positioning error of several meters down to a few centimeters and achieving centimeter-level accuracy. Under good conditions, horizontal errors can be held to about 2–3 cm (0.8–1.2 in), and vertical errors to about 3–5 cm (1.2–2.0 in). This centimeter-level accuracy is sufficient to meet the precision standards required in civil surveying and construction management.

With RTK, which provides high-precision position information on-site in real time, you can efficiently check on the spot whether the graded ground has reached the specified elevation and whether the slope matches the design. The immediacy of being able to confirm numeric values as soon as they are measured is a major advantage not available with conventional optical levels or total stations. RTK is therefore a key technology for improving productivity in the era of smart construction and on-site DX. The Ministry of Land, Infrastructure, Transport and Tourism recommends using GNSS positioning as part of ICT construction in *i-Construction*, and RTK-based high-precision surveying is increasingly being adopted across many sites.

How introducing RTK changes grading work (labor savings and efficiency)

Introducing RTK significantly changes how grading work and elevation management are carried out on site. Traditionally, operators relied on benchmarks called 丁張（ちょうはり） and many stakes (杭（くい）) with height marks; an operator and separate staff would use an optical level to confirm elevations while grading. This method required manpower and time, and on large sites moving between survey points and resetting equipment took time. By using RTK surveying, these traditional surveying processes can be greatly simplified and streamlined.

The main benefits of introducing RTK are as follows:

• One-person operation possible: Tasks that previously required two or more people for elevation checks and surveying can be completed by a single person with RTK. There is no need to assign multiple survey staff separate from the heavy equipment operator; a single person can handle ground elevation checks and staking (layout) work.

• Measure wide areas in a short time: With RTK-GNSS surveying, corrections from the base station allow direct acquisition of absolute coordinates (latitude, longitude, elevation) at arbitrary points on the site. Since distant points can be measured without sequential lines of sight like a total station, you can simply walk with the antenna across a large grading site to quickly observe ground elevations at many locations, greatly reducing work time.

• Confirm results in real time: You can immediately confirm the measured elevation and position numbers on the spot, allowing instant decisions such as “how many cm (inches) of fill are needed to reach the design elevation” or “is the slope deviating from the required gradient.” You can perform additional measurements or give corrective instructions to the heavy equipment operator in real time as needed.

• Fewer instrument relocations: With a total station, you must repeatedly move the tripod and check backsight each time the line of sight changes, but with RTK, once the base station is set up (or a network RTK is used), you can continuously measure by simply moving the rover antenna around the site. This reduces frequent instrument relocations and simplifies setup tasks.

• Measurement possible without relying on highly skilled techniques: Traditional layout with strings, staff reading, and total station operation required skill, but RTK equipment displays elevation and position numerically, so once you learn the basic operations, even less experienced staff can perform measurements to a consistent standard. Combined with user-friendly dedicated software, RTK approaches “surveying anyone can do.”

As described above, introducing RTK greatly reduces labor and improves efficiency in surveying tasks related to grading, while delivering high-accuracy measurement data. On large development sites, RTK enables quick checks of elevations across the whole site, preventing overlooked surface irregularities and improving construction quality. In an industry facing serious labor shortages, one-person RTK surveying can be a lifesaving solution for sites. Against the backdrop of DX and *i-Construction*, GNSS-based surveying methods are expected to become even more widespread.

How to efficiently check slope and elevation with RTK

So how can you actually use RTK to check ground slope and elevation? Here are concrete methods and key points.

• Measure many points to understand the terrain: For as-built (出来形（できがた）) control, surface measurements are essential to confirm that the finished shape matches the design. With an RTK-GNSS receiver, a single person can walk the site with an antenna and record latitude, longitude, and elevation data at each location by pressing a button. For example, where conventional leveling measured every tens of meters, RTK can increase the number of survey points on a fine grid and still finish quickly. Plotting the many acquired points on a map lets you grasp even slight undulations of the ground surface in detail. For slope checks, you can calculate gradients from elevation differences between multiple points or visually confirm via automatically generated contours and color maps from the survey data. RTK surveying, which can rapidly measure extensive areas in detail, is a powerful tool for improving quality control beyond what manual methods can achieve.

• Pass/fail judgment by comparison with design values: Elevation data obtained with RTK can be compared against prepared design elevation references or 3D model data to instantly evaluate construction quality. By comparing measured elevation at each point with the design elevation, you can check whether filling or cutting heights are within the allowable range and whether the slope of roadbeds or floors matches the instructions. Many RTK-compatible surveying software packages automatically calculate and display differences from the design (e.g., “+3 cm (1.2 in)”, “-2 cm (0.8 in)”) when you import observed point data. This streamlines inspection work and lets you immediately identify problem areas on site. For example, when checking longitudinal road gradients, measure the start, end, and intermediate elevations with RTK and judge on site whether they deviate from the planned alignment. If irregularities are found, you can narrow the area with additional measurements and quickly request corrective action from construction crews.

• Specific methods for measuring elevation differences and gradients: One example of slope checking with RTK is to conduct GNSS surveys at the top and bottom of a slope and compute the average gradient from the elevation difference and horizontal distance: gradient (%) = elevation difference ÷ horizontal distance × 100. Because actual terrain changes continuously, it is important to measure not only one location but also intermediate points. With RTK, you can measure multiple equally spaced points along the slope to create a longitudinal profile and examine gradient changes and surface irregularities in detail. Where levels were formerly moved and re-set on a tripod to measure elevation differences incrementally, RTK allows continuous point acquisition while walking, enabling you to collect consistent slope data in a short time.

Thus, RTK as-built surveying and slope checks are very speedy and comprehensive, allowing the collection of detailed data in a short time that would be difficult manually. As a result, post-construction quality inspections can reduce human error and oversights, enabling more reliable verification.

Points to watch when using RTK surveying

RTK surveying is convenient and highly accurate, but there are points and limitations to be aware of when introducing and operating it. Here are items to keep in mind on-site.

• Dependence on the positioning environment: RTK accuracy is greatly affected by the reception status of satellite signals. Open skies with many visible satellites yield high accuracy, but in narrow urban sites surrounded by high-rise buildings or in forests, signal blockage and multipath (reflections) can increase errors. In practice, suburban open sites may achieve errors of 2–3 cm (0.8–1.2 in), while in city streets temporary deviations of over 10 cm (3.9 in) have been reported. Therefore, do not overtrust RTK in places with poor sky visibility; when necessary, flexibly cross-check with conventional total station or leveling surveys.

• Vertical accuracy and handling elevation references: GNSS positioning tends to have lower accuracy in the vertical direction than in the horizontal. Even with RTK, vertical errors of several centimeters may remain, so be careful in situations requiring millimeter-level strict height control. For measurements that demand strict absolute elevation—such as verifying concrete thickness—effective measures include comparing RTK results with known height reference points obtained by leveling and correcting, or rechecking critical heights with an optical level. Also, verifying that RTK height data is stable by comparing with reference points or repeating measurements increases reliability.

• Initialization and securing sufficient satellites: RTK achieves full accuracy only after obtaining a carrier-phase fixed solution (Fix). Immediately after starting positioning or when satellite geometry is poor, it may take time to obtain a fixed solution, and even after achieving Fix, the solution can revert to a float solution for various reasons. It is desirable to predict GNSS satellite geometry (e.g., GDOP) and select time windows suitable for surveying. Also, avoid measuring in periods with few visible satellites or strong ionospheric effects; sometimes pausing measurement is appropriate. Using high-performance receivers that support multiple frequencies and multiple satellite systems (not only GPS but also GLONASS, Galileo, QZSS, etc.) is effective for stable positioning.

• Dependence on equipment and communications: If you use network RTK (see below), the communication link is the lifeline of RTK positioning. In mountainous areas or near underground structures, mobile communication may be out of range, preventing receipt of correction data and making RTK positioning impossible. Equipment failure or battery depletion also interrupts work. To prepare, carry spare batteries, set up your own base station with radio corrections when mobile coverage is expected to be poor, or switch to post-processed positioning—saving logs and processing later—as a fallback.

• Reliability of deliverables and official use: If RTK-collected survey data will be submitted as official deliverables or inspected by third parties, be prepared to explain GNSS-specific processing and error characteristics. For instance, land registry surveys that require legally assured accuracy may demand supporting documents (observation records, accuracy verification) even for points observed with RTK. Survey regulations also recommend accuracy management such as comparing GNSS observations with known control points and preserving observation logs. While RTK alone may suffice for on-site checks, for official inspections it is prudent to retain verification data from total stations or other instruments. RTK dramatically improves work efficiency, but do not rely on it exclusively; perform double checks at key points with traditional methods to ensure accuracy and reliability.

If operated appropriately while being mindful of the above points, RTK surveying becomes a very powerful tool. Understand environmental conditions, combine RTK and conventional surveying as appropriate, and maximize RTK benefits while controlling risks.

Simple surveying with LRTK

To fully leverage RTK technology on-site, having easy-to-use equipment and systems is also important. Until recently, RTK surveying required specialized and expensive equipment and complex setup, but now solutions like LRTK make it easy for anyone to adopt RTK surveying.

LRTK is an all-in-one surveying system that combines a compact high-performance GNSS antenna that attaches to a smartphone or tablet with dedicated mobile apps and cloud services. With this setup, a smartphone becomes a high-precision GNSS receiver without the need for large surveying instruments, and intuitive app operations allow centimeter-level positioning and surveying. For example, with LRTK, even staff with limited surveying experience can perform precise position measurements and sophisticated stakeout tasks. Tasks that previously required two people, such as stake placement, can now be performed by one person guided accurately by AR navigation features integrated with LRTK.

The emergence of the LRTK series has significantly lowered the barriers to RTK adoption for small and medium construction companies and local governments. The latest LRTK solutions support the Ministry of Land, Infrastructure, Transport and Tourism’s *i-Construction* and are attracting attention as tools that dramatically improve on-site productivity and surveying accuracy. If you want to perform one-person RTK surveying but are unsure what equipment and workflow to prepare, LRTK packages devices, apps, and cloud services together for smooth deployment. They are designed with cost and ease of operation in mind, making them accessible even to companies without in-house surveying departments.

As RTK becomes more widespread, surveying work will shift from “skilled artisan techniques” to “digital tasks anyone can perform.” Leading this shift is simple surveying with LRTK, which has the potential to change conventional on-site assumptions. By adopting LRTK to perform high-precision, efficient RTK surveying easily, consider creating a small revolution in your company’s construction management.

FAQ

Q: How accurate is RTK surveying? Is RTK alone really sufficient? A: With RTK-GNSS surveying, under good conditions you can achieve about 2–3 cm (0.8–1.2 in) horizontally and about 3–4 cm (1.2–1.6 in) vertically. This accuracy largely meets the control precision required in civil engineering such as road and earthwork projects, and in many cases RTK alone is sufficient. However, in environments with poor satellite reception—such as urban canyons or forests—temporary errors on the order of tens of centimeters (several inches to a few feet) can occur. Depending on conditions, consider supplementing RTK with traditional methods. The important point is to perform double checks—such as verifying RTK measurements with other methods—so you can operate with confidence.

Q: If we have RTK, are total stations and levels no longer necessary? A: RTK is a very useful tool, but it does not entirely replace total stations (TS) or optical levels. Each instrument has its strengths. RTK efficiently measures many points over wide areas and can position where line of sight is not available, but for measurements requiring millimeter-level accuracy or for precise elevation setting under clear line-of-sight conditions, TS and optical levels still offer higher precision. Ideally, use RTK for the portions it covers efficiently, and complement it with TS or levels for final refinements such as exact benchmark setting or precise elevation control—thereby leveraging the advantages of both.

Q: What is required to use network RTK? A: To use network RTK (such as VRS), in addition to the rover GNSS receiver, you need an environment that can receive correction data over the Internet. Specifically, the rover must have mobile connectivity (either a receiver with a built-in SIM or a smartphone tethering connection), and you must subscribe to a correction service (GNSS reference station network). In Japan, in addition to paid high-precision correction services by private providers, there are free correction data distribution services using Geospatial Information Authority of Japan electronic reference stations; connecting to these services enables RTK positioning without setting up your own base station. However, in remote mountainous sites without mobile coverage, network RTK cannot be used; in such cases, you need to set up a local base station and transmit corrections by radio or switch to post-processing later.

Q: I’m planning to introduce RTK surveying for the first time. Can a beginner handle it easily? A: Recent RTK equipment and software are designed to be user-friendly, and basic operations are not very difficult. Systems like LRTK enable measurements by simply following on-screen guidance in a smartphone app, so those with little technical knowledge can use them. However, getting maximum accuracy from RTK requires some tips: avoid placing obstructions directly above the antenna, extend the pole as high as practical, choose times with favorable satellite geometry, and record after the positioning result has stabilized. Start practicing in open areas with good satellite reception, measure the same point multiple times to check variability, and gain experience. If unsure, consult manufacturers or providers. With proper learning and practice, beginners can master RTK surveying on-site in a relatively short time.

Q: What is “simple surveying with LRTK”? A: LRTK is a solution that combines a small RTK-GNSS receiver compatible with smartphones and a dedicated app to enable anyone to perform centimeter-level surveying (simple surveying) without specialized large equipment or complex setup. For example, by attaching an LRTK receiver to a smartphone and walking the site, high-precision position data is automatically recorded and managed in the cloud. Tasks that were traditionally performed by experienced surveyors, such as stakeout and as-built control, can be accomplished accurately by less experienced engineers using intuitive AR navigation in LRTK. In short, “simple surveying with LRTK” means realizing RTK-level accuracy with easier equipment and operation, and this new surveying method is beginning to prove effective at many sites.