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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, 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).
Put simply, GNSS is a broad term that covers GPS 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 maintained 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 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 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 signals too, the rover calculates its position with centimeter-level accuracy. Learn more about RTK in this article.
Are there any limitations to using GNSS?
Despite its clear advantages, 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 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:
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.
- RTK corrections explained: from base station to NTRIP service
- Introducing Emlid Reach RX: pocket-sized RTK GNSS receiver
- Basics of RTK GPS and GNSS for non-surveyors
- Accuracy and precision explained: surveying with high precision GPS