GNSS vs GPS: what is the difference?

In the world of surveying and drone mapping, accuracy is everything—and that starts with understanding the technology that makes it possible. You’ve probably heard the terms GPS and GNSS tossed around, but while they’re often used interchangeably, they actually refer to different levels of satellite navigation systems. In this article, we’ll dive into what GNSS is, how GPS fits into the picture, what is the difference between GNSS and GPS and why GNSS is a game changer for surveyors.

What is GNSS?

The term “GNSS” (Global Navigation Satellite Systems) refers to a network of satellite constellations that provide continuous precise positioning and timing information worldwide. GNSS includes several satellite constellations maintained by different countries. There are four constellations GPS (USA), GLONASS (Russia), Galileo (EU), and BeiDou (China) with global coverage and as two regional systems QZSS (Japan) and IRNSS or NAVIC (India).

GPS	Global Positioning System	United States	31 satellites
GLONASS	Globalnaya Navigatsionnaya Sputnikovaya Sistema	Russia	24 satellites
Galileo	Europe’s own global navigation satellite system	European Union	23 satellites
BeiDou	BeiDou Navigation Satellite System	China	44 satellites
QZSS	Quasi-Zenith Satellite System	Japan	4 satellites
IRNSS	Indian Regional Navigation Satellite System	India	7 satellites

Put simply, GNSS is a term that covers GPS system and other similar systems operated by different countries. Each GNSS system uses its own set of satellites and ground-based control networks, enabling various devices equipped with GNSS receivers to achieve high precision by combining signals from multiple systems.

What is GPS?

GPS (Global Positioning System), developed and operated by the United States, was the first widely available satellite navigation system. Its long-standing use and integration into countless consumer devices over the years have made it a household name.

Additionally, many devices, such as smartphones and car navigation systems, use the term “GPS” even when they rely on signals from multiple GNSS systems for more accurate positioning. Since “GPS” is the term most widely recognized by consumers, manufacturers and app developers often label their services as “GPS,” even when they are utilizing the broader GNSS network.

This widespread familiarity has led to “GPS” becoming synonymous with satellite navigation, even though it’s just one part of the broader Global Navigation Satellite Systems (GNSS). Most people aren’t aware that GPS system along with other systems like GLONASS (Russia), Galileo (EU), and BeiDou (China), form GNSS.

What lies behind every system in GNSS?

Every Global Navigation Satellite System (GNSS) relies on three segments—space, control, and user—that must work perfectly together.

The space segment consists of satellites orbiting 20,000 to 37,000 kilometers above Earth, constantly broadcasting signals about their geographical position and time. Satellites determine their position through constant communication with ground control stations, which track their location, monitor their orbits, and update the satellites’ onboard systems with the correct positional information. The user segment includes devices that receive GNSS signals and calculate positions using special algorithms.

Combining signals from multiple satellite systems effectively addresses the need for more reliable positioning. This provides broader global coverage and reduces blind spots. However, GNSS devices provide meter-level accuracy due to factors like atmospheric interference, signal reflection (multipath), poor satellite geometry, and minor timing errors. While this is sufficient for everyday use, specialized techniques like Differential Global Positioning System (DGPS), not to be confused with the U.S. GPS constellation, or Real-Time Kinematic (RTK) can boost accuracy to centimeter-level for applications like surveying and mapping.

What is DGPS?

DGPS boosts the positional data from GPS technology and GNSS by using ground-based reference stations to correct signal errors. These stations compare GNSS data with their known locations and broadcast corrections to nearby receivers. As a result, DGPS improves positioning accuracy from around 5-10 meters to 1-3 meters.

Other GNSS constellations also utilize special systems to achieve a similar accuracy level of several meters. This is usually sufficient for everyday tasks like vehicle or smartphone navigation, but it falls short for precise applications such as surveying and mapping.

What is RTK?

In the case of surveying and mapping, where centimeter accuracy is crucial, Real-Time Kinematic (RTK) technology comes to help. RTK is a technique that helps us to calculate the coordinates with centimeter-level accuracy in real-time. The technique involves using one stationary reference receiver called a base station, and one moving receiver called a rover. The base receives data from satellites and transmits them, together with its own position, to the rover. Using these data and receiving satellite positioning signals too, the rover calculates its position with centimeter-level accuracy and reliability.

Are there any limitations to using GNSS?

Despite its clear advantages, widely used GNSS does have some limitations. Tall buildings, trees, and other obstacles can block signals, reducing accuracy—especially in urban environments or dense forests where it’s difficult to maintain a strong satellite connection.

Another challenge is multipath interference, where satellite signals bounce off surfaces like buildings or the ground, causing the receiver to pick up multiple signals at slightly different times. This results in inaccurate positioning.

GNSS performance can also be affected by atmospheric conditions, such as ionospheric and tropospheric delays, which distort the signal as it passes through different layers of the atmosphere.

To minimize these issues and ensure optimal accuracy, it’s best to place GNSS receivers in open areas with an unobstructed sky view above 30 degrees, free from potential obstacles that could block or reflect signals.

How accurate are GNSS technology constellations?

The accuracy of different GNSS constellations varies based on several factors, including the quality of the receiver, the environment, and whether correction techniques (such as RTK) are used. However, each constellation has its inherent capabilities and accuracy ranges:

System	Accuracy	Details
GPS	• Standard GPS: 3-5 meters • With DGPS: 0.5-1 meter • With RTK: Centimeter-level accuracy	GPS is the oldest and most widely used system, offering reliable positioning worldwide. Civilian-grade receivers typically experience meter-level accuracy, but with correction techniques, accuracy can reach centimeters.
GLONASS	• Standard GLONASS: 3-7 meters • With DGPS: 1-2 meters • With RTK: Centimeter-level accuracy	GLONASS generally provides slightly less accuracy than GPS in standalone use but is often used in combination with GPS to improve overall accuracy. GLONASS also has a slightly different orbital setup, which can be advantageous in high latitudes (closer to the poles).
Galileo	• Standard Galileo: 1 meter • High-Accuracy Service (HAS): Less than 20 centimeters • With RTK: Centimeter-level accuracy	Galileo is a newer system with advanced signal technology, providing higher accuracy than GPS and GLONASS in standalone mode. With the free Galileo High Accuracy Service (HAS), it offers location data with sub-meter accuracy.
BeiDou	• Standard BeiDou: 2.5-5 meters • With SBAS (Satellite-Based Augmentation System): 1 meter • With RTK: Centimeter-level accuracy	BeiDou is particularly accurate in the Asia-Pacific region, where its regional coverage is optimized. In global applications, BeiDou provides similar accuracy to GPS and Galileo. With SBAS, it can offer a meter-level accuracy.
QZSS	• Standard QZSS: 1-3 meters • With SBAS: Sub-meter to centimeter-level accuracy	QZSS, also known as Michibiki, primarily enhances GPS accuracy in the Asia-Pacific region, especially Japan. It works in tandem with GPS to improve performance in urban canyons and areas with poor satellite visibility
IRNSS	• Standard IRNSS: 5-20 meters • With SBAS: Sub-meter to meter-level accuracy with SBAS • With RTK: Centimeter-level accuracy	IRNSS, also known as NavIC (Navigation with Indian Constellation), provides accurate positioning services primarily over India and surrounding regions. Used with augmentation, it offers sub-meter to meter-level accuracy.

Reach GNSS receivers for accurate surveying

If you are looking for surveying equipment, consider Reach RS3. This is an easy-to-use RTK GNSS receiver with centimeter precision. If you need to collect data in hard-to-reach places at greater angles or need a connection to a third-party base, Reach RS3 is tailored for this. It comes with the handy Emlid Flow mobile app and the Emlid Flow 360 web application. Reach RS3 is available in the Emlid online store and ships worldwide.