Comparison for Small-Scale Projects: RTK vs Total Station

Table of Contents

• Introduction

• What is a Total Station?

• What is RTK Surveying?

• Comparison of Work Time

• Comparison of Cost

• Accuracy Comparison

• Simple Surveying with LRTK

• Conclusion

• FAQ

Introduction

In the construction and surveying industries, the term “RTK” has attracted attention in recent years. What are the differences between traditional optical surveying (using a total station) and the latest GNSS surveying technology, RTK surveying? For small-scale surveying projects, many people wonder which method is more efficient and advantageous. Questions such as “Is RTK surveying truly high-precision? Is it cost-effective?” may arise.

This article compares RTK surveying and total station surveying from three perspectives—“work time,” “cost,” and “accuracy”—and explains the advantages and disadvantages of each, as well as points for using them on small sites. We hope this will be useful for those considering streamlining or labor-saving measures in surveying operations.

What is a Total Station?

A total station (TS) is an electronic optical surveying instrument that has long been widely used on surveying sites. It integrates an angle-measuring theodolite for measuring horizontal and vertical angles with an electro-optical distance meter (EDM) for measuring distances, and by aiming at a surveying prism (reflector) as a target, it can obtain three-dimensional coordinates with high precision using a single unit. Its accuracy is very high, and over short distances errors can be confined to the millimeter level (mm, in), so, for example, even a survey point 500 m (1640.4 ft) away can achieve an error on the order of ±3 mm (±0.12 in). It has long been a mainstay for precise positioning in architecture and civil engineering. Also, because optical distance measurement does not rely on radio waves, it can be used at night or in bad weather and provides stable measurements for various targets, including metal surfaces. Since it does not rely on satellite positioning, it can measure in tunnels or forests as long as line of sight is maintained, which is a major strength in environments where GNSS cannot be used.

Typically, a total station is mounted on a tripod for use. It is set up on known control points and leveled, and after performing back-sighting and other alignment procedures, measurements begin. The surveyor looks through the TS telescope and sights the staff with the prism, observing angles and distances. On large sites, obstacles and line-of-sight issues may require multiple re-setups (relocating the instrument), and each time alignment and error adjustments must be performed. Also, it is basically a two-person operation—one person operating the machine and another holding the prism at the target point—so it requires manpower and time (robotic TS models can be operated by one person but the equipment is expensive).

What is RTK Surveying?

RTK (Real Time Kinematic) surveying is a GNSS positioning technique that uses satellites such as GPS and enhances positioning accuracy in real time. It is generally performed using two GNSS receivers: a rover (mobile unit) and a base (reference station). The base is installed on a point with known coordinates, and the error information of the satellite signals received there is sent to the rover via radio or the Internet; the rover applies corrections to its position solution, allowing it to determine positions in real time with centimeter-level accuracy (this high-precision solution is called a “FIX solution”). Whereas standalone GPS has errors on the order of meters, RTK eliminates those errors through relative positioning with the base, achieving a dramatic improvement in accuracy.

RTK surveying has the advantage that, as long as satellites can be received, absolute coordinates can be obtained over a wide area. When measuring multiple points, each point is obtained as a relative coordinate with respect to the same base station, so errors between measurement points do not tend to accumulate even over large areas. Moreover, if the base is set on a known point in a public coordinate system (such as the global geodetic system), the obtained coordinates become public coordinate values directly, making it easy to compare measured data later with design drawings or GIS positions. Actual accuracy is said to be about 1–2 cm (0.4–0.8 in) horizontally and about 2–3 cm (0.8–1.2 in) in elevation, which is sufficient for typical civil engineering surveys and construction control. Furthermore, by using network RTK services such as public reference station networks, surveying can be performed with only a rover without setting up your own base. However, RTK is heavily dependent on satellite signal reception, so in areas like downtown high-rise districts, forests, or tunnels a fixed (centimeter-level) solution may not be obtainable and positioning may fail. In such cases, conventional use of total stations or other methods may still be necessary.

Comparison of Work Time

In terms of work efficiency and required time, RTK surveying is markedly faster than total station surveying. With a total station, setup of the instrument and back-sighting for positioning preparation take time, and when measuring multiple points you must move along with the staff carrying the prism and observe one point at a time. If there are obstacles, you must either set up the instrument around them or remove and re-set it at another location, and on large sites these re-set operations may need to be repeated many times. These procedures prolong the surveying time on site.

On the other hand, once the base station setup (or connection to the network) is complete for RTK surveying, a single worker carrying the rover can walk the site and obtain coordinates instantly by pressing a button at the desired points. Because there is no need to secure line of sight or relocate equipment, continuous observations can be made efficiently even when there are many points. In extreme cases, an RTK survey of a large airport site reported observation times of about 10 seconds per point, allowing work that previously required several people and a full day to be completed in a few hours. The ability to obtain coordinates in real time reduces wasted time by enabling immediate on-site data checks and decisions about the next measurement point, and overall RTK greatly shortens the time required for surveying. Also, RTK can be completed by one person, reducing communication loss and contributing to efficient, well-organized surveying.

Comparison of Cost

RTK surveying also has attractive advantages for small-scale projects from a cost perspective. First, regarding labor costs, if a conventional total station survey that required two people a full day can be completed by one person in about half a day with RTK, labor costs can be significantly reduced. Shorter work times also reduce waiting time for heavy equipment and other tasks, producing indirect cost savings. In small-budget projects, compressing surveying labor costs directly reduces overall costs.

However, attention must be paid to equipment acquisition costs. High-performance total stations and RTK-capable GNSS receivers are both expensive, and the latest models of either can require investment on the order of several million yen. In addition to regular calibration and consumable replacements (batteries, etc.) for total stations, RTK may incur communication costs and subscription fees for correction data services. Judged by initial investment alone, the hurdle for introducing RTK is not necessarily low. Nevertheless, with the recent reduction in GNSS receiver prices and the emergence of low-cost RTK solutions using smartphones, it is becoming possible to implement high-precision positioning at a more affordable cost than before. Also, using network RTK (e.g., VRS) eliminates the need to set up your own base station, reducing the number of devices required, though it does entail paying for correction services. In Japan, however, universities and local governments sometimes offer public RTK reference station services, and the Geospatial Information Authority provides electronic reference station data free or at low cost, so with some ingenuity running costs can be kept down.

Overall, investment in RTK surveying can pay off in the medium to long term. The significant reduction in effort and time for surveying work leads to labor savings and schedule shortening benefits that can outweigh the initial equipment costs. For companies operating many sites, one RTK equipment set can improve efficiency across multiple projects, yielding high cost-effectiveness. Small contractors can also flexibly use network RTK services only for the required period to enjoy RTK benefits at low cost. Renting high-precision GNSS equipment as needed has also become easier, offering an option to introduce RTK while keeping initial expenses down.

Accuracy Comparison

Regarding positioning accuracy, total stations and RTK have different strengths due to their differing basic principles. Total stations have very high relative accuracy in both angles and distances over short ranges, capable of millimeter-level precision, making them strong for situations that require minimizing errors to the utmost—such as precise layout of structures or displacement measurement. RTK surveying, by contrast, typically achieves horizontal accuracy of about 1–2 cm (0.4–0.8 in) (often 3–4 cm in actual measurement) and does not reach the millimeter precision of TS. However, RTK can cover a wide area simultaneously and directly obtain absolute coordinates. When surveying multiple points, total stations can accumulate small errors each time the instrument is re-set, whereas RTK obtains each point as a relative measurement to the common base, meaning errors between distant points are less likely to accumulate.

Comparing vertical accuracy, total station combined with leveling has the advantage. Leveling with a TS can determine height differences with errors of a few millimeters, whereas RTK vertical accuracy is generally about ±2–3 cm (±0.8–1.2 in). However, for typical civil engineering surveys and earthwork management, an accuracy of a few centimeters is often sufficient, and RTK is practically acceptable in most cases. In fact, the Geospatial Information Authority of Japan sets RTK survey standards at within 15 mm (0.59 in) horizontally and within 50 mm (1.97 in) vertically, which falls within the allowable accuracy for ordinary surveying work. In short, except for special cases that require “millimeter-level absolute accuracy,” RTK surveying can deliver accuracy comparable to a total station for small-scale sites. Again, however, RTK depends on satellite reception, so if a FIX solution cannot be obtained under building shadows or under tree cover, accuracy will temporarily degrade. In such environments it is important not to insist on RTK and to flexibly cover with TS or other complementary methods.

Simple Surveying with LRTK

A recent advancement in RTK technology is a solution called “LRTK.” LRTK evolves conventional RTK surveying further and enables more straightforward and mobile high-precision positioning. One major feature is that by receiving dedicated correction data via satellite communication or proprietary networks, centimeter-level (cm (in)) positioning is possible without installing a base station. This eliminates the need for prior base station preparation, and surveying can be started immediately by simply powering up the receiver on site. It is essentially a “base-station-free RTK” concept, allowing surveyors to carry a compact LRTK device into the field and quickly obtain high-precision survey data.

LRTK is a system that utilizes GNSS receivers and smartphone apps and is designed for intuitive operation even on sites where RTK is new to users. The equipment configuration is compact and portable, and the fact that each worker can handle their own high-precision positioning tool is innovative. Actual implementations have reported cases where topographic surveys that used to take several days were completed in a few hours with LRTK, or where real-time measurement of road or track displacements enabled immediate repair decisions. Enabling high-precision, rapid surveying directly contributes to shorter schedules and cost savings, and makes efficient single-person surveying feasible where it was previously difficult. Even for small-scale surveying projects, using LRTK allows site condition monitoring and quantity control with minimal personnel and time, so its spread is expected to continue. Note that the LRTK series is compatible with the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction initiative, and is attracting attention as a solution supporting digitalization (DX) in the construction industry.

Conclusion

For small-scale surveying projects, it is necessary to produce results efficiently with limited personnel and time. Therefore, when choosing surveying equipment, it is important to strike a balance between work efficiency and the required accuracy. If the required accuracy is on the order of a few centimeters in an open site, using RTK surveying can greatly reduce work time and costs. On the other hand, in environments where satellite signals cannot reach or where millimeter-level precision is required, the conventional total station is a reliable choice.

Furthermore, recent solutions such as LRTK have lowered the barriers to RTK, and by incorporating these appropriately, even small projects can potentially be surveyed faster and at lower cost than before. Leveraging advances in surveying technology can help improve on-site productivity. If surveying is not a bottleneck, other tasks can be advanced earlier, leading to overall schedule shortening. With chronic labor shortages, the use of such labor-saving technologies can be a significant help to the surveying industry.

FAQ

Q: What is RTK surveying? A: RTK is a surveying method that uses two GNSS receivers—a base and a rover—and performs real-time error corrections to achieve centimeter-level high-precision positioning. The rover receives correction information from the base and corrects its GPS-derived position to achieve high accuracy. The feature is the ability to obtain much more precise positions on site in real time than standalone GPS.

Q: Which is more accurate, a total station or RTK? A: For fine detail, a total station is more accurate. A TS can achieve millimeter precision over short distances; for example, a target 100 m (328.1 ft) away can have an error on the order of a few millimeters. RTK accuracy is on the order of several centimeters horizontally. However, in general surveying work RTK’s centimeter-level accuracy is sufficient in many cases, and unless extraordinarily high precision is required the practical difference is minimal. For situations demanding millimeter-level precision, TS is preferred; otherwise RTK can handle most tasks without issue.

Q: Can RTK completely replace the total station? A: RTK cannot replace total stations in all situations. RTK cannot be used indoors, in tunnels, or in dense forests where satellites cannot be received, so TS and other methods remain necessary in such locations. Also, TS is better for measurements requiring millimeter precision. However, in open outdoor surveying RTK can handle the majority of work, so the best approach currently is to use them according to the situation.

Q: What equipment and preparation are needed for RTK surveying? A: Basically, a set of high-precision GNSS receivers (for base and rover) is required. You also need radios or Internet connectivity to link them, a tripod for installing the base, and known coordinates (control point coordinates) for the base location. If using a network RTK service (e.g., VRS), surveying is possible with only a rover receiver, since correction data are received over the Internet and base setup is unnecessary. Note that when using certain low-power radios between base and rover, licenses or notifications for radio stations may be required.

Q: Which surveying method should I choose for small sites? A: In open environments, RTK surveying is often more suitable for small-scale projects because it enables efficient surveying with fewer people and less time. It requires less setup and teardown, and provides coordinates on the spot. However, in confined sites surrounded by buildings or in forests where satellites are hard to capture, RTK may be unusable, and a total station should be used. Similarly, when extremely high accuracy is required, TS is the safe choice. The key is to choose between RTK and TS based on site conditions and required accuracy. In some cases, measuring most points with RTK and supplementing detailed areas with TS is an effective hybrid approach.

Q: What is LRTK? A: LRTK is a modern RTK solution designed to make traditional RTK surveying easier. By using dedicated correction data, centimeter-level positioning is possible without a base station, allowing immediate high-precision surveying on site if the receiver and communication environment are available. It features convenient operation via smartphone apps and is designed so that a single person can quickly survey small sites. LRTK is a technology that dramatically enhances the convenience of RTK.