RTK GPS vs GNSS: A Complete Comparison — Positioning Accuracy and How to Choose for Field Personnel

In surveying and civil engineering and construction sites, the terms "RTK GPS" and "GNSS" are being heard more frequently. However, the reality is that surprisingly few practitioners accurately understand the differences between these two terms and the disparities in their positioning accuracy. This article explains, from the basic differences between RTK GPS and GNSS to how to choose between them on site, in an easy-to-understand, practitioner-oriented manner.

Table of Contents

• What is the fundamental difference between GNSS and GPS?

• What is RTK: How real-time kinematic positioning works

• Accuracy comparison between standalone GNSS positioning and RTK positioning

• Worksites that require RTK positioning and those that do not

• Naming differences between RTK GNSS and RTK GPS

• How to choose between the base-station method and the network method

• Understanding factors that affect positioning accuracy

• Key points for equipment selection and items to verify in practice

• Easily introduce RTK positioning on-site with LRTK

What is the fundamental difference between GNSS and GPS?

GPS is the name of the satellite positioning system operated by the United States (Global Positioning System). On the other hand, GNSS is an abbreviation for Global Navigation Satellite System and is a collective term for multiple satellite positioning systems such as GPS, Russia's GLONASS, the EU's Galileo, and Japan's Michibiki. In other words, GPS is a type of GNSS, and the term GNSS refers to a broader concept.

Modern positioning devices are almost all compatible with multi-GNSS, and by receiving multiple satellite systems simultaneously they improve positioning accuracy and stability. In the field this is often called "GPS surveying," but in reality most cases involve GNSS positioning.

What is RTK: The Mechanism of Real-Time Kinematic Positioning

RTK (Real-Time Kinematic) is a technical method for dramatically improving the accuracy of satellite positioning. In ordinary standalone positioning, errors of several meters or more can occur, but with RTK positioning, by exchanging correction data in real time between a base station and a rover, an accuracy of approximately 1-2 cm (0.4-0.8 in) can be achieved in both the horizontal and vertical directions.

To briefly explain how RTK works: first, a base station installed at a known coordinate receives satellite signals and generates correction information for error components that can be calculated from its own position (such as ionospheric delay and tropospheric delay). Next, this correction information is transmitted in real time to the rover via radio or cellular networks, and by applying those corrections on the rover side, high-precision positioning becomes possible. The term "RTK GPS" refers to technology that uses GPS (or GNSS) for RTK positioning.

Accuracy Comparison Between Standalone GNSS Positioning and RTK Positioning

There is a large difference in accuracy between standalone GNSS positioning and RTK positioning. In the case of standalone positioning using the GPS receivers built into smartphones or typical car navigation systems, even under ideal conditions the horizontal error is approximately 3〜5 m (9.8〜16.4 ft). In urban environments with building shadows or dense tree cover, errors of 10 m or more (32.8 ft or more) are not uncommon.

On the other hand, with RTK positioning, horizontal accuracy of about 1-2 cm (0.4-0.8 in) and vertical accuracy of about 2-3 cm (0.8-1.2 in) can be achieved. This difference in accuracy is decisive in every field where positional precision is required, such as surveying, construction, agriculture, and drone operations.

As a concrete example, consider the case of constructing along the centerline of a drainage channel 30 cm (11.8 in) wide: with the error of standalone GPS positioning, the construction position cannot be determined at all, but with RTK positioning the discrepancy between the design and the field construction can be kept within a few centimeters (a few inches).

Sites That Require RTK Positioning and Those That Do Not

RTK positioning is not required at every worksite. Choosing an appropriate positioning method based on the task and required accuracy leads to cost optimization.

Typical situations that require RTK positioning include boundary determination surveying, control point surveying, installation of batter boards, installation of ground control points for drone surveying, management of seeding and fertilization positions in precision agriculture, and final inspections of infrastructure facilities. All of these are tasks for which legal and technical requirements demand accuracy on the order of a few centimeters.

Conversely, situations in which standalone GNSS positioning is sufficient include rough on-site location checks, route guidance, large-area land-use mapping, and basic input of GIS information. Clearly defining the purpose of the work and the required accuracy is the starting point for equipment selection.

Naming differences between RTK GNSS and RTK GPS

The term "RTK GPS" is mainly a holdover from the early days when only GPS was used. Most commercially available high-precision positioning devices today are multi-GNSS compatible and use multiple satellite constellations simultaneously, such as GPS, GLONASS, Galileo, and Michibiki. Therefore, technically it is more accurate to call it "RTK GNSS".

However, on-site the term "RTK GPS" is still widely used and has become established as a term referring to "high-precision RTK positioning equipment." Although the notation "GNSS" is increasingly used in equipment specifications and tender documents, colloquially "GPS" often suffices. In practice, it is important to understand the technical differences in meaning so you can accommodate both notations.

How to Choose Between the Reference Station Method and the Network Method

There are two types of RTK positioning: "single-base-station RTK," which involves installing your own base station, and "network RTK" (such as the VRS method), which receives correction information via a communications network.

Single-base-station RTK places a base station receiver at a known point and transmits correction data to the rover via radio. It can be operated even in mountainous areas and remote islands without communications infrastructure, and has the advantage of low latency. However, it involves costs and effort to install and manage the base station.

Network RTK is a service that delivers correction information from electronic reference station networks established by government agencies and private companies. In Japan, the Geospatial Information Authority's electronic reference stations and private distribution services are in place, allowing high-precision positioning with rover-only equipment. Because a base station does not need to be installed within areas with communication coverage, work efficiency is greatly improved.

It is important to choose after comprehensively assessing the on-site communication environment, work area, and operational costs.

Understanding the factors that affect positioning accuracy

Even with RTK positioning, accuracy can deteriorate depending on site conditions. Major influencing factors include multipath (reflections of satellite signals from buildings or terrain), the number and geometry of visible satellites (PDOP value), the state of the ionosphere and the troposphere, the distance between the base station and the rover (baseline length), and the condition of the antenna installation.

In particular, regarding baseline length, correction errors tend to accumulate as the distance between the reference station and the rover increases. Generally, single-reference-station RTK is recommended to be operated within a baseline length of 10–20 km (6.2–12.4 mi). Network RTK relaxes this limitation, but it depends on the quality of the correction delivery service.

To stabilize RTK positioning accuracy in the field, it is important to start measurements only after confirming that initialization (acquisition of a FIX solution) is complete, to continuously monitor whether the FIX solution is being maintained, and to install the antenna in locations with few obstructions and that are less susceptible to multipath effects.

Key Points for Equipment Selection and Items to Verify in Practice

When selecting RTK GNSS equipment, confirm the supported satellite systems, number of channels, communication methods, IP waterproof rating, battery life, and software usability. Also, depending on the work style at the site, consider the device form factor, such as pole-mounted, backpack-mounted, or drone-mounted.

In recent years, compact RTK positioning devices that can be attached to smartphones such as the iPhone have emerged, enabling smooth on-site operation while greatly reducing deployment costs compared with dedicated receivers. By pairing them with a smartphone GPS app, the combination of intuitive UI operation and high-precision positioning has been appreciated by field practitioners.

Easily Deploy RTK Positioning on Site with LRTK

LRTK (an iPhone-mounted GNSS high-precision positioning device) is a device that enables RTK positioning simply by attaching it to an existing iPhone. Because you do not need to carry a bulky dedicated receiver and it can be operated intuitively from an iPhone app, you can acquire high-precision location information in the field even without surveying expertise.

Compatible with network RTK, it can obtain a stable FIX solution across a wide area in Japan. Compared with conventional RTK equipment, it is compact and low-cost to deploy, so it can be used in a wide range of operations—not only by surveyors but also for construction management, inspections, and investigations. It is also a suitable option for sites introducing RTK positioning for the first time or for rolling it out to multiple staff.

By accurately understanding the differences between RTK GPS and GNSS and choosing the positioning solution best suited to the site’s accuracy requirements and work style, you can improve on-site productivity and ensure positioning quality.