RTK vs PPP: Which Is Better for Fieldwork?

Table of Contents

• Introduction

• What is RTK?

• What is PPP?

• Accuracy comparison between RTK and PPP

• Convergence time comparison between RTK and PPP

• Cost comparison between RTK and PPP

• Which should you use on site?

• Simple surveying with LRTK

• FAQ

Introduction

In construction and surveying, high-accuracy positioning is a critical factor that affects the quality and efficiency of projects. Standalone GPS positioning traditionally yields errors of several meters, but by utilizing high-precision GNSS positioning techniques such as RTK or PPP, errors can be reduced to several centimeters. However, because RTK and PPP differ significantly in their positioning mechanisms and characteristics, many technicians may be unsure which to use on site. This article compares RTK and PPP from the perspectives of accuracy, convergence time, and cost for survey technicians, construction managers, and others involved in positioning operations, and explains which is more suitable for fieldwork. It also touches on simple surveying using the latest technology, LRTK, and introduces future prospects for high-precision positioning.

What is RTK?

RTK (Real-Time Kinematic) positioning is a technique that uses at least two GNSS receivers—a base station and a rover—applies correction information sent from the base station in real time to cancel positioning errors, and achieves centimeter-level accuracy. The base station is installed at a known location, and the difference between the observed satellite-derived position and the precise coordinates at that point is calculated to estimate the errors. That correction information is then sent to the rover via radio or the Internet (e.g., NTRIP). By applying the received correction data to its own observations, the rover can cancel out error components present in satellite positioning and immediately compute a high-accuracy position.

The advantage of RTK is that it provides high-precision positioning in real time. While typical standalone GNSS positioning has horizontal and vertical errors on the order of several meters, RTK dramatically improves accuracy through corrections, reducing horizontal position errors to about 2-3 cm (0.8-1.2 in) and height errors to about 3-4 cm (1.2-1.6 in). This level of accuracy is sufficient for civil engineering surveys and automatic control of construction machinery, and the ability to obtain centimeter accuracy immediately is a major appeal of RTK. Because RTK is a relative positioning method, the closer the base station and rover are to each other, the more common-mode errors can be shared and the more stably high accuracy can be maintained (typically used within several km to several tens of km).

In recent years, network RTK (VRS and similar) using the Geospatial Information Authority of Japan’s continuous reference station network has been developed, allowing rovers to receive correction information via mobile communications and share base stations over wide areas. RTK is now effectively the standard technology for high-precision positioning in construction and surveying and is widely used for tasks that require accuracy on site, such as stakeout and as-built measurement.

What is PPP?

PPP (Precise Point Positioning) is a positioning method that achieves centimeter-level accuracy with a single GNSS receiver. Unlike RTK, it does not require a nearby base station; the receiver improves positioning accuracy by incorporating precise satellite orbit and clock data, as well as corrections for ionospheric and tropospheric delays.

Specifically, PPP uses global correction data provided by organizations such as the International GNSS Service (IGS)—corrections for satellite orbit errors, atomic clock offsets, and ionospheric/tropospheric effects—and applies these corrections in the receiver’s computation to obtain a high-precision position. Because PPP is absolute positioning in the geocentric coordinate system rather than relative to a base station, it has the advantage that accuracy degradation due to distance is minimal even across regions or countries. It is also suitable for applications that require stable long-term observations, such as crustal deformation monitoring or establishing large-area reference points.

However, PPP has a major drawback of requiring a long initial convergence time. In real time, it typically takes several minutes to several tens of minutes from the start of positioning to reach final centimeter-level accuracy. Although accuracy improves gradually with prolonged static observation, obtaining high precision immediately while moving is difficult, making PPP generally unsuitable for real-time field operations. Moreover, real-time PPP often requires subscription to commercial precise correction services (delivered via satellite or the Internet) and a high-performance GNSS receiver capable of processing such data, which raises the barrier to adoption.

Recently, methods such as PPP-RTK (real-time reduction of PPP convergence time) and SSR (State Space Representation) have emerged to address this convergence-time issue. For example, Japan’s Quasi-Zenith Satellite System "Michibiki" offers a centimeter-level augmentation service (CLAS) that broadcasts regional high-accuracy correction information from satellites and enables single receivers to achieve centimeter-level positioning in relatively short times. This makes it increasingly possible to obtain high accuracy without a base station even where mobile communications are unavailable. Nevertheless, standard PPP still requires waiting time from the start of positioning until the desired accuracy is achieved, so it remains unsuitable for construction sites where immediate responsiveness is required.

Accuracy comparison between RTK and PPP

Both RTK and PPP can achieve very high accuracy with appropriate measures, but they differ in how that accuracy appears and how stable it is. Under good observation conditions, RTK can provide real-time horizontal accuracy of about 2-3 cm (0.8-1.2 in) and vertical accuracy of about 3-4 cm (1.2-1.6 in). PPP can also converge to errors on the order of several centimeters given sufficient static observation time. However, immediately after starting positioning, PPP typically contains errors on the order of several tens of centimeters to about 1 m (3.3 ft), and those errors gradually decrease over time. In other words, RTK provides nearly centimeter accuracy from the start, whereas PPP approaches centimeter accuracy over time.

Also, because RTK is relative positioning, accuracy and solution stability can degrade if the distance to the base station becomes too large and common-mode errors cannot be fully canceled. In contrast, PPP is absolute positioning independent of a base station, so in theory it does not suffer accuracy degradation due to distance from a base station. However, because ionospheric and tropospheric correction errors and other effects can influence instantaneous solution stability, RTK’s local corrections often better remove errors, making RTK superior in terms of moment-to-moment stability. Overall, for field tasks that require reliable centimeter accuracy in real time, RTK is considered the more dependable method. PPP can reach accuracy comparable to RTK with long-duration observations, but it is unsuitable for tasks that must be completed in a short time.

Convergence time comparison between RTK and PPP

An unavoidable consideration when using positioning on site is the difference in time from starting measurement to reaching practical accuracy (initial convergence time). In RTK, initialization from a float solution to a fixed solution is very fast when receiving correction information from a base station; under good conditions, centimeter-level accuracy can begin to be available within a few seconds to a few tens of seconds. In other words, RTK’s strength is that high-accuracy data can be used immediately after starting positioning.

On the other hand, as mentioned earlier, PPP typically requires a convergence wait time on the order of several minutes to several tens of minutes. For example, when staking out piles on site, you would want to know the high-accuracy current position for each point, but with PPP you would need to wait a long time after starting observation for the accuracy to stabilize, which is impractical. With RTK, you can determine positions within a few centimeters immediately after setting up equipment on site, making it extremely powerful for tasks that proceed while referring to successive positioning results such as stakeout and batter board work, as-built measurement, and machine guidance.

PPP is effective for applications that do not require immediate results after starting observations. Examples include establishing new reference points in remote areas where observations are taken carefully over half a day to a full day to determine precise coordinates, or long-term geodetic monitoring where a fixed point is observed for extended periods. In cases where convergence-time requirements are lax, PPP can be useful; however, for construction tasks that demand immediacy, RTK remains the appropriate choice.

Cost comparison between RTK and PPP

There are significant differences in setup and operating costs and required equipment between RTK and PPP. RTK generally requires multiple GNSS receivers for the base station and rovers. If you set up your own dedicated base station, initial investment is required for receivers, communication equipment, and installation work. However, once established, operational costs are mainly the communication fees between the rover and the base station. Alternatively, by subscribing to network RTK services (VRS, etc.) that use the Geospatial Information Authority of Japan’s network, you can receive correction information without deploying your own base station, though service fees (monthly or annual) apply.

PPP requires only a single receiver for positioning, so the equipment configuration is simple. However, to obtain real-time centimeter-level accuracy with PPP, you often need to subscribe to commercial high-precision correction distribution services (via satellite or Internet). These services deliver correction data via dedicated satellites (geostationary) or continuous online streams. High-performance GNSS receivers capable of processing those signals (multi-frequency, multi-GNSS support) may be required, which can be very expensive. On the other hand, if you use PPP in post-processing (post-analysis), you can obtain precise orbit and clock data from IGS and analyze for free, so PPP can be a low-cost way to achieve high accuracy when time is not an issue.

In summary, RTK provides high accuracy but requires multiple pieces of equipment and possibly base station setup, which involves time and cost up front. PPP is simpler in terms of hardware but often requires service subscriptions and high-performance equipment for immediate use. In the past, assembling a full RTK kit was a significant hurdle and difficult for small- to medium-sized sites. However, recent advances in low-cost GNSS receivers and communication technologies have produced compact, affordable RTK solutions, making RTK increasingly accessible.

Which should you use on site?

Considering the differences above, let’s think about which to use on actual construction and surveying sites. The conclusion is that RTK is suitable for most on-site operations. For tasks that require checking centimeter-level positioning in real time—such as staking out, as-built control, and the like—RTK’s real-time performance and stability are highly effective. Although prerequisites such as base station installation and communication environment need to be arranged, if these can be prepared, RTK will dramatically improve on-site efficiency and accuracy.

PPP is generally less used as the main tool on construction sites due to its inferior real-time performance. However, PPP (or PPP-RTK) becomes a viable option when you cannot set up a base station due to lack of communication infrastructure—such as in mountainous areas or remote islands—or when you need to obtain absolute high-accuracy coordinates at remote locations by a single operator. For example, when you need to measure coordinates of observation points dispersed across remote locations using a common reference, or detect ground movement via long-term fixed-point observation, PPP’s characteristics can be well suited.

In summary, RTK is field-oriented for needs that require knowing high-accuracy positions immediately on site, while PPP is suitable for needs that accept some waiting time and require wide-area high-precision positioning without communications or base stations. It is important to understand both methods’ characteristics and choose according to site conditions and application.

Simple surveying with LRTK

RTK is a high-precision, field-oriented positioning technology, but traditionally it required expensive dedicated equipment and specialized knowledge, making adoption difficult for small- to medium-sized sites or limited personnel. A solution that lowers these barriers is LRTK, which enables simple surveying using smartphones.

LRTK (Lightweight RTK) is a next-generation solution that transforms a smartphone into a centimeter-level surveying instrument using a small RTK-GNSS receiver that can be attached to the phone and a dedicated app. By attaching an ultra-compact receiver device with an integrated antenna to a smartphone and connecting via Bluetooth, RTK positioning can be performed without cumbersome cables or stationary base stations. The pocket-sized equipment weighing a few hundred grams is easy to carry to the site. When needed, turning on the smartphone and receiver allows immediate centimeter accuracy positioning of the current location without complex initial setup.

Furthermore, LRTK supports Japan’s Michibiki CLAS (centimeter-level augmentation service) (half-inch accuracy) and correction data reception via the Internet, so even in areas without mobile coverage, augmentation signals from satellites can be used to maintain high-precision positioning. This means that high-precision surveying can be performed in real time anywhere—even in mountainous areas or large reclamation sites—using just a smartphone.

The advent of LRTK has transformed workflows that previously depended on specialized surveying equipment and teams, and we are moving toward an era where anyone can conduct precise surveying alone. Without costly dedicated equipment or large teams, construction managers themselves can perform positioning tasks when needed, greatly improving site productivity and operational efficiency. While understanding the advantages of RTK and PPP, consider leveraging the latest LRTK technology to determine the surveying style that best fits your organization.

FAQ

Q: What is the difference between RTK and PPP? A: RTK uses correction information from a base station to correct errors in real time and position a rover with centimeter accuracy. PPP is a method that uses precise satellite data with a single receiver to improve positioning accuracy without requiring a base station. The major differences are that RTK provides high accuracy from the start but requires infrastructure such as base stations, while PPP simplifies equipment but takes time for positioning accuracy to stabilize.

Q: Which is more accurate, RTK or PPP? A: Ultimately, both RTK and PPP can achieve centimeter-level accuracy under favorable conditions. However, RTK, being relative positioning to a base station, can consistently deliver centimeter accuracy in real time, whereas PPP requires initial convergence time and its accuracy immediately after starting is inferior. Therefore, RTK is advantageous when reliable real-time accuracy is needed.

Q: Are there benefits to using PPP on site? A: PPP is useful when you need wide-area positioning but cannot provide communications or a base station. For example, in deep mountain locations where base station signals cannot reach, or when you need to obtain absolute coordinates at multiple remote points without a base station, PPP enables single-operator completion of positioning tasks. However, because it does not provide immediate results, its benefits are limited for tasks like stakeout or as-built control that require instant results.

Q: What is required to implement RTK? A: Traditional RTK requires at least one GNSS receiver for a base station installed at a known point and one rover receiver for mobile positioning. A communication method linking the two (radio or Internet-based NTRIP service) is also necessary. If using a network RTK service, a contract with the service provider and compatible receivers are required. Recently, solutions like LRTK—combining a smartphone and a small receiver—have appeared, expanding options to start centimeter-level positioning without assembling a full set of dedicated equipment.

Q: What is PPP-RTK? A: PPP-RTK is a new technology that combines the ease of PPP with the immediacy of RTK. By combining correction information from satellites and ground reference networks, it shortens PPP’s long convergence time. A representative example in Japan is Michibiki’s CLAS, which broadcasts regional error corrections from satellites in real time, allowing a single receiver to achieve centimeter-level accuracy in a short time. PPP-RTK is making “immediate centimeter accuracy without a base station” increasingly feasible.

Q: Is it possible to perform high-precision surveying alone? A: Yes. Recently, single-person high-precision surveying has become possible. For example, using LRTK—a combination of a smartphone and a small RTK receiver—one person can perform centimeter-level surveying in the field. This eliminates the need for multiple personnel and large equipment, enabling small teams to perform surveying tasks efficiently.