Table of Contents

• What is optical surveying (level & total station)?

• What is RTK surveying?

• Comparison of work efficiency

• Comparison of accuracy and error management

• Other differences (environmental adaptability, cost, operation)

• Recommendation: simplified surveying with LRTK

• FAQ

What are the differences in surveying approach and achievable accuracy between optical instruments (levels and total stations) and the increasingly prominent RTK surveying (Real Time Kinematic)? By comparing the traditional optical surveying methods and the latest GNSS positioning technology RTK, we examine the advantages and disadvantages of each. This article focuses particularly on work efficiency and error management, explaining which method is superior in which aspects. We hope this will help surveying beginners and field personnel choose the optimal surveying method for their needs.

What is optical surveying (level & total station)?

Optical surveying refers to a conventional surveying method that measures angles, distances, and heights using dedicated optical instruments. Typical instruments include the level (spirit level) and the total station (TS). Although their uses differ, both require the observer to look through a telescope to sight a target and optically measure relative positions.

• Level (levelling): A level is an instrument for precisely measuring elevation differences. By mounting a telescope-equipped level on a tripod and setting it horizontal, the reading on a graduated staff yields height differences. Level surveying is characterized by extremely small vertical errors; even over several kilometers of levelling, millimeter-level accuracy can be expected. However, since it cannot measure horizontal position (plan coordinates), it is mainly used for elevation or settlement measurements.

• Total station (TS) surveying: A total station is an electronic optical instrument that simultaneously measures horizontal angle, vertical angle, and slope distance. It integrates an theodolite (for angles) and an electronic distance meter, and by sighting a prism target can compute the target’s 3D coordinates. In TS surveying, the workflow typically involves setting up the instrument over a known control point, orienting by back-sighting or resection to determine the instrument’s position, then placing prisms at survey points and observing angles and distances. TS accuracy is extremely high: for short distances, distance measurements can be on the order of ±2-3 mm (±0.08-0.12 in), and angles can be measured to the arc-second level (1" = 1/3600 of a degree). When operated properly by a skilled operator, optical methods can achieve the highest levels of precision.

Advantages of optical surveying: Optical surveying with dedicated instruments offers the following benefits.

• High-precision measurement: Levels and TS deliver millimeter-level precision for relative measurements over short distances. Especially for vertical control, combining a level can suppress errors to well below a few millimeters, making it powerful where precise elevation control is required.

• Stable observations: Optical methods can be used at night or in cloudy weather without concern for radio interference, and distance measurement to metal surfaces is possible. They are less affected by weather or material properties, providing stable measurements.

• Usable wherever there is line of sight: As long as the target is visible, measurements are possible, so observations can be made inside tunnels or in forests (by ensuring prism line of sight) where satellite signals cannot reach. In urban areas, measurements are possible if a prism is visible between building canyons.

Disadvantages of optical surveying: There are, however, weaknesses inherent to the traditional approach.

• Labor- and time-intensive: TS surveying is basically a two-person operation (one operates the instrument, the other holds the prism or reads the staff), which increases labor costs. Robotic total stations allow single-person operation but are very expensive, and for large areas the tripod must still be relocated repeatedly. Each point measurement takes time and effort, making it inefficient for large quantities of points.

• Line-of-sight and distance constraints: Measurements require an unobstructed line of sight between instrument and prism. Points blocked by buildings or terrain cannot be measured directly, requiring additional survey points or detours. There is also a maximum practical distance, and angular or distance errors accumulate over longer distances (see closure error below). On large sites the equipment must be moved many times, each time requiring network accuracy management (error adjustment).

• Equipment handling and expertise: Total stations and precision levels are expensive, requiring regular calibration and maintenance. Setup and measurement demand specialist knowledge and experience, which takes time to acquire. For beginners, these instruments present a steep learning curve.

What is RTK surveying?

RTK surveying (Real Time Kinematic) is a surveying method that uses GNSS (Global Navigation Satellite Systems) to correct positioning errors in real time and determine positions at centimeter-level accuracy. RTK uses two high-precision GNSS receivers: a base station and a rover. The base station is set up on a known point (with accurate coordinates) and sends error information from received satellite signals to the rover, which applies corrections to achieve high-precision positioning.

In simple terms, ordinary GPS positioning has meter-level errors, but RTK uses the carrier phase of the satellite signal to cancel errors. By comparing the signals received simultaneously by the base and rover from the same satellites, common error components (such as atmospheric delays or satellite orbit errors) are removed, and the remaining tiny differences allow computing relative positions with high precision. Because this process operates in real time, centimeter-level coordinates can be obtained on site immediately.

RTK surveying workflow:

• Base station setup: A GNSS antenna and receiver (base) are set up on a known point within the survey area. The base computes the real-time corrections for the satellite signals based on its known position.

• Rover observations: The surveyor carries the rover GNSS antenna on a pole and takes observations at the desired points. The rover receives correction data from the base via radio or the internet (e.g., NTRIP) and applies corrections to the positioning solution.

• Coordinate acquisition: The corrected solution at the rover becomes a high-precision position (a FIX solution) within a few centimeters. The operator waits for the receiver to report a FIX solution and records the coordinates at that point. Repeating this at multiple points yields multiple 3D coordinates in real time.

RTK accuracy: Generally, RTK-GNSS surveying achieves about ±1-2 cm horizontally and ±2-3 cm vertically. However, this depends on satellite geometry, distance to the base station, and local environment. For example, within a few km of the base station RTK usually attains centimeter accuracy, but in environments where trees or buildings block the sky, fewer satellites are received and accuracy degrades. Multipath (signal reflection) from buildings can cause deviations of several tens of centimeters in positioning results. Thus, in terms of absolute millimeter stability, optical surveying (TS + level) can still have an edge. Nonetheless, RTK’s advantages—measuring many points at once over a wide area, being able to start without ground control, and immediate verification of results—make it sufficient for most practical civil engineering surveying tasks.

Advantages of RTK surveying: Adopting RTK provides benefits not available with conventional methods.

• Work efficiency and labor savings: RTK surveying is basically a one-person workflow. A surveyor carrying the rover can walk the site and acquire coordinates at each point by pressing a button, allowing fast coverage of large areas. Because there is no need to maintain line-of-sight between instrument and prism or to repeatedly re-set equipment, the number of points observable per day increases dramatically. Reported cases show that in open, unobstructed sites, control-point observations with RTK took about 10 s per point. Tasks that previously required several people and tens of minutes per point with a TS can be completed quickly by one person with RTK.

• Wide-area surveying and immediate results: Because RTK uses satellite positioning, it can measure distant points without accumulating errors between them; for example, points several kilometers apart can be obtained via the base station without error accumulation. Data are obtained as coordinates in real time, allowing on-the-spot verification and comparison with design values. Post-processing for coordinate computation or drawing conversion is largely unnecessary, facilitating data integration.

• Easy acquisition of absolute coordinates: If the base station is set on a known point in a global geodetic system, each survey point’s coordinates are directly obtained in that datum as absolute coordinates. With TS, converting local measurements to a public coordinate system requires multiple control points and transformation from a local system; RTK provides global coordinates on site, eliminating this post-processing step.

Disadvantages of RTK surveying: There are caveats to RTK as well.

• Dependence on satellite signals: RTK’s biggest weakness is its reliance on satellite reception. In areas with tall buildings or in dense forests, satellites may be blocked and sufficient accuracy cannot be achieved. GNSS positioning is generally unavailable in tunnels or underground spaces, requiring reliance on optical instruments like total stations in those environments.

• Initial investment cost: RTK requires two high-precision GNSS receivers, and a full set typically costs several million yen (hundreds of thousands of dollars equivalent), making the equipment expensive. Like high-end robotic TS or 3D laser scanners, precision surveying equipment is a significant investment. However, recent technological advances have produced lower-cost GNSS units, and network RTK services provided by national or local agencies reduce the initial hurdle.

• Expertise and operation: Operating RTK requires knowledge of GNSS and communications. Understanding satellite geometry and ionospheric effects, configuring base station data formats, and setting up radio or NTRIP connections are necessary. Because continuous communication is needed, sites without mobile coverage may require radio equipment or a switch to post-processing (PPK) if real-time is impractical. While these operational challenges exist, modern systems have become more user-friendly, and once mastered they can be operated stably.

Comparison of work efficiency

RTK and optical surveying show substantial differences in work efficiency, especially in required personnel and time.

• Staffing: Traditional TS surveying typically uses teams of 2–3 people: one sets up and operates the instrument, another carries the prism, and sometimes another handles recording or safety. RTK surveying, by contrast, is usually completed by a single person. A technician carrying a rover with receiver can walk the site and observe successive points, directly addressing labor shortages and enabling manpower reduction. Given current challenges in recruiting construction workers, RTK allows efficient surveying with small teams.

• Measurement speed: With a TS, each point requires angle and distance measurement and recording, and when the instrument is relocated the position must be recalculated by resection and network error adjustments performed. With RTK, after setting a base station the rover can continuously observe points while walking. As soon as the solution becomes FIX, the operator records the point name and moves on, dramatically reducing measurement time. Because there is no time loss for line-of-sight or equipment relocation, RTK can obtain many more points per day than TS. In practice, for as-built control point collection on large development sites, RTK allows one person to walk the area and finish the same tasks in far less time than repeated TS setups.

• Simplified preparation: Because RTK yields coordinates in real time, pre- and post-survey tasks are reduced. TS surveying requires a detailed survey plan, establishment of a control network, and post-survey closure error calculations and adjustments. With RTK, the survey plan after base setup is relatively simple, and coordinates for each point are immediately determined, often eliminating the need for later network adjustment. On-site verification and additional measurements can be done immediately, reducing rework.

Comparison of accuracy and error management

Differences in accuracy and error management are also key when comparing the two methods. Optical surveying with total stations and levels offers extremely high relative accuracy over short distances, whereas RTK excels in absolute accuracy over wide areas.

• Short-range precision: Total stations especially provide millimeter-order accuracy for short distances. For tasks demanding millimeter accuracy—such as centering structural columns or precision equipment installation—TS plus level surveying remains indispensable. For strict vertical control, second-order levelling may be used, achieving accuracies that RTK (typically with centimeter-level vertical errors) cannot match. The advantage of optical methods is that within a limited area they can suppress errors to the utmost.

• Wide-area bulk surveying: RTK’s accuracy is about 1–2 cm in plan, and it can maintain that accuracy uniformly across large areas. TS surveying requires teams to relocate and splice survey networks as the site expands; small measurement errors during this process accumulate and cause positional discrepancies between distant points (closure error). Survey computations distribute these discrepancies across the network, but large adjustments increase uncertainty. With RTK, points are obtained relative to a common base station, so error accumulation is minimized and consistent high-accuracy positioning across distant points is possible. Actual measurements using network RTK have reported errors of around 3–4 cm even between points several km apart, which is sufficient for routine civil engineering tasks such as as-built control and batter-board setting.

• Accuracy standards for public surveying: In Japan’s public surveying standards, RTK-derived point accuracy is defined as within 15 mm horizontally and within 50 mm in height. In other words, errors within that range are acceptable for public works surveying results. Conversely, levelling can achieve astonishingly tight vertical control—within a few millimeters over line surveys of several kilometers—but large-area levelling requires sectional adjustments. Overall, except in cases requiring millimeter-level precision, RTK generally provides practically sufficient accuracy. For error management on site, validating RTK points against known control points at key locations provides assurance for using RTK survey results.

• Environment-dependent errors: Environmental factors also affect accuracy. Optical surveying maintains high precision as long as line of sight is available and can operate day or night regardless of weather, but efficiency suffers in cluttered sites. RTK performs excellently in open areas but becomes unusable where satellites cannot be observed. Thus, each method suits different site conditions, and in practice it is advisable to use them complementarily depending on circumstances.

Other differences (environmental adaptability, cost, operation)

There are various other differences between RTK and optical methods.

• Adaptability to site conditions: The advantage can reverse depending on site conditions. In dense urban canyons, thick forests, or indoor/underground spaces, RTK cannot capture satellites and is not useful, whereas TS and levels can often adapt by ensuring line of sight. Conversely, RTK is powerful on large development sites or disaster areas where there are no ground control points. If the sky is open, RTK can survey long distances even in mountainous areas. Understanding the characteristics of both methods and choosing flexibly according to the environment is important.

• Acquisition and operating costs: Looking only at equipment prices, high-performance total stations and RTK GNSS receivers both run into the millions of yen (hundreds of thousands of dollars), so initial costs are substantial. However, RTK offers cost benefits through labor savings and reduced construction time. For example, if a job that used to take two people two days can be done by one person in one day, labor cost savings are significant. Shorter working times also reduce indirect costs like heavy-equipment idle time. Running costs differ: TS mainly requires calibration and consumables, while RTK incurs communication fees and possibly correction service fees. In Japan, public data such as electronic reference point data from the Geospatial Information Authority can sometimes be used free of charge, helping reduce operating costs. Overall, the productivity gains from RTK often make it a long-term payoff investment.

• Operability and data integration: Traditional optical instruments, while accurate when operated by experts, require manual recording of each point and thus extra effort to digitize and share data. RTK devices require specialized setup initially, but once a FIX solution is obtained observation data are automatically stored as electronic coordinates. Because post-survey calculations are unnecessary, data can be directly imported into CAD or BIM software, making RTK highly compatible with downstream workflows. With ICT construction and i-Construction initiatives, RTK has advantages for data integration.

Recommendation: simplified surveying with LRTK

A recent evolution in RTK technology is LRTK. LRTK is a solution that further simplifies RTK operation while achieving high-precision surveying. Its key feature is that it can receive dedicated correction data via satellite or the internet so that real-time positioning is possible without installing a local base station. In other words, without carrying a heavy base station set, you can start centimeter-level positioning as soon as you enter the survey area. This greatly reduces equipment preparation and shortens initial setup time. Once the receiver is turned on and satellites are acquired, observations can begin immediately, dramatically improving mobility.

LRTK accuracy and benefits: Compared with conventional RTK, LRTK provides equal or better positioning accuracy (within a few centimeters) reliably. Because correction data can be obtained from a wide-area source, base relocation or switching is unnecessary even on large sites. In short, LRTK’s strength is being “RTK without being tied to a local base.” Surveyors can carry a compact LRTK receiver set and start high-precision surveying anywhere. Field cases report using LRTK GNSS receivers to rapidly map road settlement over an area that previously took days, completing the job in hours. Railway track inspections with LRTK have enabled workers to walk with equipment and detect track displacement in real time, making on-the-spot repair decisions. LRTK makes possible the combination of labor savings and immediacy that was difficult with traditional total stations.

Thus, LRTK incorporates the strengths of both RTK and optical surveying and significantly contributes to field productivity. High-precision, fast surveying shortens construction time and reduces costs; the ability for one person to cover large areas also addresses labor shortages. Equipment is compact and easy to handle, and LRTK is designed to be accessible even for first-time RTK adopters. If your site needs more efficient or labor-saving surveying, consider adopting simplified surveying with the latest LRTK solutions.

FAQ

Q: What accuracy can RTK surveying actually achieve? A: It depends on conditions, but typically about 1–2 cm horizontally and 2–3 cm in elevation. However, satellite reception conditions affect accuracy and FIX solutions may not always be achievable. In clear, open conditions RTK performs well, but under difficult conditions deviations of several tens of centimeters can occur.

Q: Can RTK surveying be done by one person? A: Yes. RTK surveying is generally a one-person operation. A worker carrying the rover antenna and receiver can patrol the site and acquire coordinates by operating a button at the desired points. Unlike TS surveying, no separate prism-holder is required, enabling efficient surveying even with limited manpower.

Q: Are there environments or situations where RTK cannot be used? A: RTK cannot function where satellites cannot be received—narrow urban alleys, tunnel interiors, deep forest, etc., where signals are blocked or reflected and high-precision positioning is impossible. In such places, optical instruments like total stations and levels are still necessary. RTK may also be interrupted in severe thunderstorm conditions or when radio conditions are extremely poor.

Q: Will total stations and levelling become unnecessary in the future? A: While RTK has streamlined many surveying tasks, optical surveying will not disappear. Millimeter-level precision and surveying in satellite-denied environments mean TS and levelling remain essential. The key is complementary use: RTK can replace many routine topographic and as-built surveys, but for final reference heights or millimeter-critical checks, combining RTK with levelling is prudent.

Q: What is LRTK? How is it different from ordinary RTK? A: LRTK is an advanced RTK technology that makes operation more convenient. The major difference is that LRTK does not require installing a personal base station on site. By using dedicated correction networks or satellite augmentation signals, a rover-only setup can achieve centimeter-level positioning in real time. In short, you can go to the site with a single equipment set and start high-precision positioning immediately. LRTK’s positioning accuracy is generally equivalent to standard RTK, and because no base station setup is required it shortens preparation time and improves efficiency for wide-area surveying.