Table of Contents

• Introduction

• What is RTK?

• What is PPP?

• Accuracy Comparison: RTK vs PPP

• Convergence Time Comparison: RTK vs PPP

• Cost Comparison: RTK vs PPP

• Which to Use on Site?

• Simple Surveying with LRTK

• FAQ

Introduction

High-precision positioning is a critical factor that affects the quality and efficiency of construction and surveying projects. Standalone GPS positioning traditionally incurs errors of several meters (several ft), but by using high-precision GNSS positioning techniques such as RTK or PPP, errors can be reduced to several centimeters (several in). That said, RTK and PPP differ greatly in their positioning mechanisms and characteristics, so many field engineers may be unsure which to use. This article compares RTK and PPP from the perspectives of accuracy, convergence time, and cost, and explains which is more suitable for field use for survey technicians and construction managers involved in positioning tasks. It also touches on simple surveying using the latest technology LRTK and introduces prospects for future high-precision positioning.

What is RTK?

RTK (Real-Time Kinematic) positioning is a technique that achieves centimeter-level accuracy by using at least two GNSS receivers—a base station and a rover—and applying correction data sent from the base station in real time to cancel positioning errors. The base station is set up at a known position, and the error is estimated by calculating the difference between the observed satellite-derived position at that site and its true coordinates. That correction information is then transmitted to the rover via radio or the internet (e.g., NTRIP). By applying the received correction data to its own observations, the rover can offset the error sources in satellite positioning and compute a high-precision position instantaneously.

The advantage of RTK is that it provides high-precision positioning results in real time. While typical standalone GNSS positioning has horizontal and vertical errors on the order of several meters (several ft), RTK’s corrections dramatically improve accuracy to about 2–3 cm (0.8–1.2 in) horizontally and about 3–4 cm (1.2–1.6 in) in height. This level of accuracy is sufficient for civil engineering surveying and automatic control of construction machinery, and the ability to obtain centimeter precision immediately is a major appeal of RTK. Because RTK is a relative positioning method, the closer the base and rover are to each other, the more common-mode errors can be canceled, maintaining stable high accuracy (typically used within several km to several tens of km (several km (a few thousand ft) to several tens of km (tens of thousands of ft))).

In recent years, network RTK using national permanent GNSS networks (e.g., VRS methods) has been developed so that rovers can receive correction information via cellular communication and share base stations over wide areas. RTK is now the de facto standard technology for high-precision positioning in construction and surveying and is widely used for tasks on site that require accuracy, such as stakeout and as-built measurement.

What is PPP?

PPP (Precise Point Positioning) is a positioning method that can achieve 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 information and corrections for ionospheric and tropospheric delays.

Specifically, PPP uses global correction data provided by organizations such as the International GNSS Service (IGS)—including satellite orbit errors, atomic clock offsets, and ionospheric/tropospheric correction values—and the receiver applies these corrections in its calculations to compute a high-precision position. Because PPP is absolute positioning in an Earth-centered coordinate system rather than relative to a local base station, it has the advantage that accuracy does not degrade with distance across regions or countries. It is also suitable for applications that require stable positions over long periods, such as crustal deformation monitoring or establishing widely distributed reference points.

However, PPP has a major drawback: it requires a substantial initial convergence time. In real time, it commonly takes several minutes to several tens of minutes from the start of positioning to reach final centimeter-level accuracy. While accuracy improves gradually if you remain stationary and continue observing, obtaining high precision instantly while moving is difficult, making PPP generally unsuitable for immediate field operations. Real-time PPP often requires subscription services that deliver precise correction data via satellite communication or the internet (paid services) and sometimes high-performance GNSS receivers capable of processing such data, so the entry barrier can be higher.

Recently, methods such as PPP-RTK (real-time shortening of high-precision standalone positioning) and SSR (State Space Representation) have emerged to address convergence time. For example, Japan’s Quasi-Zenith Satellite System “Michibiki” offers a centimeter-level positioning augmentation service (CLAS) that broadcasts region-specific high-precision corrections from satellites, enabling single receivers to achieve centimeter-level positioning in a relatively short time. This increases the number of cases where high precision can be obtained without a base station even where cellular coverage is absent. Nevertheless, conventional PPP still involves waiting for the solution to converge from the start of positioning to the desired accuracy, so it is currently not well-suited to time-critical construction site tasks.

Accuracy Comparison: RTK vs PPP

Both RTK and PPP can achieve extremely high accuracy with proper techniques, but they differ in how that accuracy manifests and in stability. Under good observation conditions, RTK can provide about 2–3 cm (0.8–1.2 in) horizontal accuracy and about 3–4 cm (1.2–1.6 in) vertical accuracy in real time. PPP can also converge to errors of a few centimeters if stationary for a sufficient time and accumulating data. However, immediately after starting positioning, PPP typically still includes errors of several tens of centimeters to about 1 m (tens of cm to about 3.3 ft), and the errors gradually decrease over time. In other words, RTK provides almost centimeter accuracy from the outset, whereas PPP approaches centimeter accuracy over time.

Also, because RTK is relative positioning, accuracy and solution stability can degrade if the base and rover are too far apart and common errors cannot be fully canceled. PPP, being an absolute positioning method that does not depend on a base station, theoretically does not suffer accuracy degradation due to distance from a base station. However, because ionospheric and tropospheric correction errors can have an effect, RTK’s local corrections often outperform PPP in terms of instantaneous solution stability. Overall, for field tasks that require reliable centimeter-level accuracy in real time, RTK is considered the more dependable method. PPP can reach RTK-comparable accuracy if measured over long periods, but it is unsuitable for tasks that must be completed quickly.

Convergence Time Comparison: RTK vs PPP

An unavoidable practical consideration when using positioning on site is the time from starting measurements to reaching usable accuracy (initial convergence time). For RTK, initialization from a “float” solution to a “fixed” solution is very fast when receiving corrections from a base station, and under good conditions centimeter-level accuracy can begin to be obtained within several seconds to several tens of seconds. In other words, RTK’s strength is that you can use high-precision data almost immediately after starting positioning.

By contrast, PPP generally requires a convergence wait on the order of minutes to tens of minutes, as noted above. For example, when staking out positions at a site, you usually want to know high-precision coordinates point by point, but with PPP you would have to wait a long time from the start of observation for the accuracy to stabilize, which is impractical. With RTK, you can determine positions within a few centimeters right after setting up equipment on site, making it powerful for tasks like stakeout, batter-board work, as-built measurement, and machine guidance where you proceed while referring to successive positioning results.

PPP is useful when you do not need immediate results after starting observations. For instance, when establishing new control points in remote areas where you can spend half a day to a full day observing to determine accurate coordinates, or for geological monitoring where long-term fixed-point observations are made. In cases where convergence time requirements are relaxed, PPP can be valuable, but for any field work that requires immediacy, RTK is the better choice.

Cost Comparison: RTK vs PPP

There are also major differences in the costs and required equipment for introducing and operating RTK and PPP. RTK generally requires multiple GNSS receivers for the base and rover. If you set up your own dedicated base station, initial investment is needed for receivers, communication equipment, and base station installation work. Once built, operating costs are mainly limited to communication fees between rover and base. Alternatively, subscribing to network RTK services (VRS, etc.) that use national permanent GNSS networks allows you to obtain corrections without hosting your own base station, but service fees (monthly or annual) apply.

PPP positioning itself can be completed with a single receiver, making the equipment configuration simple. However, to obtain centimeter-level accuracy in real time with PPP, you often need to subscribe to commercial real-time correction distribution services (via satellite or internet). These services involve receiving correction data from dedicated satellites (geostationary) or continuously obtaining correction information online. They also typically require high-performance GNSS receivers capable of processing those signals (multi-frequency, multi-GNSS support), which can be very expensive. On the other hand, if you use PPP in post-processing, you can obtain precise orbit and clock data from IGS and process it for free, so PPP can be a cost-effective route to high accuracy when time is not a constraint.

In summary, RTK delivers high accuracy but requires multiple pieces of equipment and base station setup, entailing preparation time and cost. PPP is simpler in terms of equipment but often necessitates service subscriptions and high-performance receivers for immediate use. In the past, assembling a full RTK system was a significant hurdle and difficult for small to medium-sized sites to adopt. However, recent advances in low-cost GNSS receivers and communications have produced smaller, cheaper RTK solutions, making RTK increasingly accessible.

Which to Use on Site?

Considering the differences above, let’s consider which to use in actual construction and surveying sites. The conclusion is that RTK is suitable for most field operations. For tasks like stakeout and as-built management where you need to verify centimeter-level positions immediately as you work, RTK’s real-time performance and stability are highly effective. While base station installation and communication environment preparation are prerequisites, if those conditions can be arranged, RTK can dramatically improve field efficiency and accuracy.

PPP, being inferior in real-time responsiveness, is rarely the primary choice on construction sites. However, PPP (or PPP-RTK) can be a strong option when base stations cannot be established, such as in mountainous areas or remote islands without communication infrastructure, or when you want to obtain absolute high-precision coordinates at isolated remote sites. PPP is also suitable when you need to measure coordinates of multiple dispersed remote points in a common reference frame or when you want to detect ground movement through long-term fixed-point observation.

In short, RTK is field-friendly when you need to know a high-precision position immediately on site, while PPP is appropriate when you are willing to wait and want wide-area, high-precision positioning without communications or base stations. Understanding the characteristics of both and choosing according to site conditions and use cases is important.

Simple Surveying with LRTK

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

LRTK (Lightweight RTK) is a next-generation solution that turns a smartphone into a centimeter-level surveying instrument by attaching a small RTK-GNSS receiver to the phone and using a dedicated app. By mounting a compact receiver device with an integrated antenna on a smartphone and connecting via Bluetooth or similar, RTK positioning can be performed without cumbersome cables or a stationary base station. The pocket-sized equipment weighing several hundred grams provides convenient portability to the field. Turn on the phone and receiver when needed, and you can instantly measure your current position with centimeter accuracy without complex initial setup.

LRTK also supports Japan’s Michibiki CLAS (centimeter-class augmentation service) and receiving correction data via the internet, so even in areas without cellular coverage you can continue high-precision positioning using augmentation signals from satellites. That means you can perform real-time, high-precision surveying anywhere—mountainous areas or large reclaimed sites—using just a smartphone.

The advent of LRTK is transforming tasks that once relied on specialist surveying equipment and teams, enabling anyone to perform precise surveying solo. Without expensive dedicated equipment or large crews, construction managers can carry out positioning tasks as needed, greatly improving on-site productivity and efficiency. Understand the strengths of both RTK and PPP, and consider using the latest LRTK technology to find the surveying style that best fits your company’s operations.

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 the rover at centimeter accuracy. PPP improves positioning accuracy with a single receiver by using precise satellite data and does not require a base station. RTK provides high accuracy immediately but requires base station equipment, whereas PPP has simpler equipment requirements 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 tends to provide consistently stable centimeter accuracy through relative positioning with a base station, while PPP requires an initial convergence period and is less accurate immediately after starting observations. Therefore, for real-time work that needs reliable accuracy, RTK is more advantageous.

Q: What are the benefits of using PPP on site? A: PPP is effective when you want wide-area positioning but cannot set up communication infrastructure or base stations. For example, in deep mountains where base station signals do not reach, or when you want to obtain absolute coordinates at separated points without a base station, PPP enables single-person completion of positioning. However, because it does not provide immediate results, its benefits for tasks like stakeout or as-built management are limited.

Q: What is required to introduce RTK? A: Traditional RTK requires at least one base-station GNSS receiver installed at a known point and one rover receiver for mobile positioning. Communication means to connect them (radio or internet-based NTRIP service) are also necessary. If using a network RTK service, you need a contract with the service provider and compatible receivers. Recently, solutions like LRTK that combine a smartphone with a small receiver have emerged, allowing centroid-level RTK positioning without assembling a full set of dedicated equipment.

Q: What is PPP-RTK? A: PPP-RTK combines the simplicity of PPP with the immediacy of RTK by shortening PPP’s long convergence time through a mix of corrections from satellites and ground reference networks. A representative example in Japan is Michibiki’s CLAS, which broadcasts regional correction data from satellites in real time and enables single receivers to obtain centimeter accuracy in a short time. PPP-RTK is making “instant centimeter-level positioning without a base station” increasingly possible.

Q: Is there a way for one person to perform high-precision surveying? A: Yes. Recently, one-person high-precision surveying has become feasible. For example, using LRTK that combines a smartphone with a small RTK receiver allows a single person to perform centimeter-level surveying on site. This eliminates the need for multiple people and large equipment, enabling small teams to perform surveying tasks efficiently.