RTK vs Optical (Level・TS): Comparison of Work Efficiency and Error Management

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 for simple surveying using LRTK

• FAQ

What are the differences in surveying procedure and achievable accuracy between optical surveying using traditional optical instruments (level and total station) and the increasingly popular RTK surveying (Real Time Kinematic)? By comparing the conventional optical methods with the latest GNSS positioning technology, RTK, we will examine the merits and demerits of each. This article focuses especially on work efficiency and error management, explaining which method is superior in which respects. We hope this will help survey beginners and field personnel choose the most appropriate surveying method for their needs.

What is optical surveying (level・total station)?

Optical surveying refers to the traditional surveying method that measures angles, distances, and elevations using dedicated optical instruments. Typical instruments include the level (leveling instrument) and the total station (TS). Although they serve different purposes, both require the observer to look through a telescope to sight a target and optically measure positional relationships.

• Level (leveling): A level is an instrument for precisely measuring height differences. The telescope-mounted leveling instrument is set horizontally on a tripod, and the height difference is obtained by reading graduations on a staff. Leveling is characterized by extremely small vertical errors; even leveling over several kilometers can be expected to achieve millimeter-level precision. However, since it cannot measure horizontal position (planimetric position), it is mainly used for measuring elevation or settlement amounts.

• Total station (TS) surveying: A total station is an electronic optical instrument that can simultaneously measure horizontal angle, vertical angle, and slope distance. It integrates an angle-measuring theodolite and a distance meter, and by sighting a prism target it can compute the three-dimensional coordinates of the target. In TS surveying, the instrument is set up over a known control point to determine its position via back-sighting, then prisms are placed at survey points and angles and distances are observed. The 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 level of 1 second (1/3600 of a degree). With a skilled operator and proper procedures, optical methods can achieve top-tier precision.

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

• High-precision measurement: Levels and TSs deliver millimeter-level accuracy for relative measurements over short distances. Especially in the vertical direction, using a level concurrently can keep errors to within a few millimeters or less, making it powerful where precise elevation control is required.

• Stable observations: They can be used at night or in cloudy conditions and are not affected by radio interference. Distance measurement to metallic surfaces is also possible. Their measurements are less influenced by weather or material, so they provide stable results.

• Usable wherever line of sight is available: As long as the target is visible, surveying is possible; thus, measurements can be made inside tunnels or forests where satellite signals do not reach, provided prism line of sight is secured. In urban areas, measurements are possible if the prism can be seen through building gaps.

Disadvantages of optical surveying: On the other hand, there are weaknesses inherent to conventional methods.

• Labor- and time-intensive work: TS surveying is generally performed by a team of two (one operating the instrument and the other holding the prism or reading the staff). This increases labor costs. Robotic TSs allow single-person operation, but such equipment is very expensive and, for large areas, tripod relocation is still required. Also, point-by-point measurements are time-consuming, making it inefficient for measuring large numbers of points.

• Line-of-sight and straight-distance constraints: Measurement absolutely requires no obstacles between the instrument and the prism. Points blocked by buildings or terrain cannot be measured directly; it may be necessary to add survey points or detour measurements to avoid obstacles. There is also a limit to the distance that can be measured at one time, and errors in angle and distance accumulate over long distances (see closure error below). On wide sites, the instrument must be moved repeatedly, and each move requires error adjustment (network adjustment), which is time-consuming.

• Handling equipment and required expertise: Total stations and precision levels are expensive and require periodic calibration and maintenance. Proper setup and measurement each time require specialized knowledge and experience; mastering operation takes time. For beginners, these instruments present a high handling barrier.

What is RTK surveying?

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

In brief, while ordinary GPS positioning can have errors of several meters, RTK uses the carrier-phase of the satellite signal—fine details of the wave phase—to cancel errors. The base and rover compare signals received from the same satellites at the same time and subtract common error components (ionospheric delay, satellite orbit errors, etc.), allowing the residual tiny differences to be used to compute relative position with high accuracy. Because this processing is performed in real time, centimeter-level coordinates can be obtained on site immediately.

RTK surveying workflow:

• Base station setup: A GNSS antenna and receiver (base station) are set up at a known point within the survey area. The base station calculates the real-time errors of the received satellite signals based on its precise location.

• Observations by the rover: The surveyor carries a rover GNSS antenna mounted on a pole and observes each survey point. The rover receives correction data from the base station via radio or the internet (e.g., NTRIP) and applies these corrections to the positioning solution.

• Coordinate acquisition: The corrected solution at the rover becomes a high-precision position (FIX solution) with errors within a few centimeters. The operator confirms that the receiver is in FIX and records the coordinates. Repeating this at multiple points yields three-dimensional coordinates in real time.

RTK surveying accuracy: Generally, RTK-GNSS surveying provides approximately ±1〜2 cm in horizontal position and ±2〜3 cm in vertical position. However, this varies with satellite geometry, distance from the base station, and surrounding environment. For example, within a few km of the base station, centimeter-level positioning is typically achievable, but in environments where trees or buildings block the sky, the number of visible satellites decreases and accuracy deteriorates. Multipath—where signals reflect off buildings or other objects—can cause errors of several tens of centimeters in some cases. Therefore, in terms of millimeter-level stability, optical surveying (TS＋level) still has an edge. Nonetheless, RTK’s advantages—ability to measure many points across a large area at once, ability to start surveying without known ground control, and immediate confirmation of results—are significant, and RTK generally provides sufficient accuracy for most civil engineering surveying tasks.

Advantages of RTK surveying: Introducing RTK offers benefits not available with conventional methods.

• Work efficiency and labor saving: RTK surveying is basically a one-person operation. A surveyor carrying the rover can walk the site and obtain coordinates at each point simply by pressing a button, allowing rapid progress even over large areas. Because there is no need to maintain line-of-sight between measurement points or repeatedly set up equipment, the number of points that can be observed in a day increases dramatically. In reported cases, base station control surveying in an open area without obstacles allowed observations in about 10 seconds per point using RTK. Tasks that previously required multiple people and many tens of minutes per point with TS can be completed quickly by one person with RTK.

• Wide-area surveying and immediate results: Because RTK uses satellite positioning, simultaneous measurements at distant points are possible, and coordinates can be obtained without cumulative errors even for points several kilometers apart via the base station. Since data are obtained as coordinates in real time, results can be checked on site and compared with design values immediately. Post-survey coordinate calculations or conversion to drawings are largely unnecessary, facilitating data integration.

• Easy acquisition of absolute coordinates: If the base station is set on a known point in a global geodetic datum, each survey point’s coordinates are obtained as absolute coordinates in that datum. With TS, converting measured points to a public coordinate system requires multiple control points and transformation from a local coordinate system, but with RTK you can obtain global coordinates on site and eliminate post-processing coordinate transformations.

Disadvantages of RTK surveying: RTK also has points to be mindful of.

• Dependence on satellite signals: RTK’s biggest weakness is its heavy dependence on satellite reception. In areas with tall buildings or dense forest, satellites can be blocked and high-precision positioning may be impossible. In tunnels or underground spaces, GNSS positioning is fundamentally impossible. In such places, total stations and other optical instruments must be used.

• Initial investment cost: RTK requires two high-precision GNSS receivers, and the cost of a system is typically several million yen. Like high-performance robotic TSs and 3D laser scanners, the investment is not small. However, recent advances have reduced costs with lower-priced GNSS units and network RTK services provided by governments or local authorities, lowering the initial cost barrier.

• Expertise and operation: Operating RTK requires knowledge of GNSS and communications. For example, understanding how satellite geometry and ionospheric conditions affect accuracy, configuring base station data formats, and setting up radio or NTRIP communications are necessary. Continuous communication is required, so in mountainous areas with no mobile coverage you may need to provide radios or switch to post-processing (PPK) if real-time is impractical. Although operational challenges exist, modern systems are increasingly user-friendly, and stable operation is achievable with training.

Comparison of work efficiency

There is a large difference in work efficiency between RTK and optical surveying, especially in required manpower and time.

• Personnel: Conventional TS surveying usually requires a team of 2–3 people. One sets up and operates the instrument, another carries the prism, and sometimes a third records data or handles safety. In contrast, RTK surveying is fundamentally a one-person task. A single technician carrying the rover receiver can walk the site and observe successive points, directly addressing labor shortages and enabling labor-saving operations. In today’s construction industry where securing workforce is a challenge, RTK allows efficient surveying with fewer people.

• Measurement speed: With TS, each point requires measuring angles and distances with the instrument and recording values. When the instrument must be relocated, its position must be recalculated and network adjustments made. With RTK, after setting the base station, the operator can walk around and continuously observe points with the rover. Once the solution is FIX, the operator records the point and moves on, dramatically shortening measurement time. Because there is no lost time for line-of-sight checks or instrument relocation, RTK greatly exceeds TS in the number of points that can be observed in one day. For example, in wide earthwork areas where TS would need to be re-established for each zone, RTK allows one person to walk and measure broadly, completing the same work much faster.

• Simplified setup: RTK provides coordinates in real time, reducing pre- and post-work. TS surveying requires detailed planning, establishing a control network before observation, and computing closure errors after observation for adjustment. With RTK, planning after base station setup is relatively simple, and coordinates for each point are obtained immediately, eliminating the need for later network adjustment. On-site data checking and adding missing points can be done immediately, reducing rework and increasing efficiency.

Comparison of accuracy and error management

Differences in accuracy and error management are also critical when comparing the two. Total station and level optical surveying offer extremely high relative accuracy over short distances, while RTK excels in absolute accuracy over wide areas.

• Precision over short distances: Total stations measure relative positions to millimeter order precision at short range. For tasks like setting out building column centers or precise installation, where millimeter accuracy is required, TS＋level surveying is still indispensable. For example, strict vertical control may use second-order leveling, which is in the domain where RTK would produce errors of several centimeters. The strength of optical methods is that, within a limited area, errors can be suppressed to the utmost degree.

• Bulk surveying over wide areas: RTK accuracy is around 1–2 cm in plan, but it can maintain that uniformly across a wide area. With TS, as the site expands, survey crews must relocate repeatedly and extend the network, and small measurement errors can accumulate, producing positional discrepancies between distant points (closure errors). Survey computations distribute these discrepancies across the network, but large adjustments increase uncertainty. With RTK, each point is determined relative to a common base station, so inter-point error accumulation is minimal, enabling consistent high accuracy even for distant points. In practical measurements using network RTK, errors between points several kilometers apart have been reported to remain within about 3〜4 cm (1.2〜1.6 in), which is sufficient for typical civil engineering tasks such as earthwork control and staking.

• Accuracy standards for public surveys: In Japan’s public survey standards, RTK-measured points are required to be within 15 mm in horizontal position and 50 mm in elevation. In other words, errors within that range are acceptable as survey deliverables for public works. Conversely, leveling surveys can achieve astonishing accuracy of a few millimeters even over routes of several kilometers, though for wide areas section-by-section error adjustment is needed. Overall, except in special cases requiring millimeter-level precision, RTK provides practically sufficient accuracy. For field error management, verifying RTK-obtained points against known control points at key locations allows safe use of the survey results.

• Environmental-condition errors: Environmental factors must be considered when discussing accuracy. Optical surveying maintains high accuracy day or night and in various weather as long as line of sight is secured, but its efficiency drops significantly in obstacle-dense sites. RTK performs excellently in open areas but becomes unusable where satellites cannot be captured. Thus, each method is suited to different field environments, and in actual projects it is desirable to choose or combine methods according to conditions.

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 urban canyons, dense forests, or indoor/underground spaces, RTK cannot capture satellites and is ineffective, whereas TS and levels can often cope by arranging line of sight. Conversely, RTK is powerful on vast earthwork sites or disaster areas where no ground control exists. If the sky is open, RTK can measure distant points even in mountainous areas instantly. Understanding the characteristics of both and flexibly choosing the appropriate method for the environment is important.

• Acquisition and operating costs: Looking only at equipment price, high-performance total stations and RTK-capable GNSS receivers both cost in the several-hundred-thousand-to-million-yen range, so initial costs are high for either. However, RTK’s cost benefits from reduced labor and shortened schedules should be considered. For example, if a two-person, two-day survey can be completed by one person in one day, labor costs are greatly reduced, and shorter work time reduces indirect costs such as machine idle time. As for running costs, TS mainly incurs calibration and consumables, while RTK may incur communication fees or subscription fees for correction services. That said, in Japan there are cases where Geospatial Information Authority of Japan (GSI) reference station data can be used for free, allowing operational costs to be reduced with proper planning. Overall, the dramatic improvement in survey efficiency means RTK investments typically pay off in the medium to long term.

• Operability and data integration: Traditional optical surveying instruments can be handled precisely by trained staff, but recording points manually makes digitalization and sharing more laborious. RTK equipment requires specialized initial setup, but once a FIX solution is obtained, observations are automatically stored as electronic coordinate data. Because post-survey computations are largely unnecessary, coordinates can be imported directly into CAD or BIM software, making RTK highly compatible with downstream workflows. As ICT construction and i-Construction initiatives advance, RTK has an advantage in data integration.

Recommendation for simple surveying using LRTK

A recent advancement in RTK technology is LRTK. LRTK is an evolved solution that makes high-precision surveying more convenient to operate. Its main feature is that by receiving dedicated correction information via satellite or the internet, real-time positioning is possible without setting up a local base station. In other words, you can start centimeter-accuracy positioning immediately upon entering the survey area without carrying heavy base station equipment. This greatly reduces equipment preparation and shortens on-site setup time. Once the receiver is powered on and captures satellites, observations can begin immediately, dramatically improving mobility.

LRTK accuracy and benefits: Compared to conventional RTK, LRTK provides equal or better positioning accuracy (within a few centimeters) stably. Because correction data can be obtained over a wide area, there is no need to relocate or switch base stations on large sites. In other words, LRTK’s strength is “RTK without being tied to a base station.” Surveyors can carry a compact LRTK receiver set and start surveying immediately at any site. Case studies include rapid areal measurement of road subsidence that traditionally took days but was completed in hours using an LRTK-capable GNSS receiver. Another report described railway track inspection where workers detected track displacement in real time using LRTK equipment while walking, enabling on-the-spot repair decisions. LRTK enables labor-saving and immediate surveying that was previously difficult with total stations.

Thus, LRTK incorporates the strengths of both RTK and optical surveying and greatly contributes to on-site productivity. High-precision, rapid surveying shortens construction schedules and reduces costs, and the ability for a single person to cover wide areas is effective for addressing labor shortages. The equipment is compact and easy to handle, and it is designed to be easy to introduce and operate even for first-time RTK users. If your site faces challenges such as “I want more efficient surveying” or “I want to reduce labor,” consider adopting the latest solution of simple surveying with LRTK.

FAQ

Q: What accuracy can RTK surveying actually achieve? A: It depends on conditions, but commonly horizontal accuracy is about 1〜2 cm (0.4〜0.8 in) and vertical (elevation) accuracy is about 2〜3 cm (0.8〜1.2 in). However, poor satellite reception can degrade accuracy or prevent obtaining a FIX solution, so the stated accuracy is not always guaranteed. In open, clear conditions RTK performs well, but in difficult environments errors of several tens of centimeters are possible.

Q: Can RTK surveying be done by one person? A: Yes. RTK surveying is basically a one-person operation. A worker carrying the rover antenna and receiver can walk the site and obtain coordinates at desired points by simple button operation. Unlike TS surveying, there is no need for a separate assistant to hold a prism, so RTK is efficient even on sites with limited personnel.

Q: Are there environments or situations where RTK cannot be used? A: RTK does not work where satellites cannot be received. For example, narrow urban alleys surrounded by buildings, tunnel interiors, and deep forests can block or reflect satellite signals, preventing high-precision positioning. In such places, traditional surveying with total stations or levels is necessary. Severe radio conditions during thunderstorms, etc., may also force RTK observations to be suspended.

Q: Will total stations and leveling become unnecessary in the future? A: Although RTK adoption has streamlined many surveying tasks, optical surveying will not disappear. TS and levels remain indispensable for precision measurements that require millimeter accuracy and in environments where satellites cannot reach. Thus, using each method according to the situation is important. Typical topographic surveys and earthwork control can mostly be handled by RTK, but in cases such as final reference elevation checks, combining RTK with leveling is wise.

Q: What is LRTK? How is it different from ordinary RTK? A: LRTK is a next-generation RTK technology that makes conventional RTK more convenient. The major difference is that you do not need to set up your own base station on site. By using dedicated correction networks or satellite augmentation signals, a rover alone can obtain centimeter-level accuracy in real time. In practice, you can go to the site with the receiver set and immediately begin high-precision positioning, making surveying more mobile and easier. The positioning accuracy itself is comparable to ordinary RTK, and because no base station setup is needed, preparation time is reduced and efficiency over wide-area surveys improves.