Oct 7
GNSS vs GPS: Satellite-Based Positioning Systems
- Gökçe Bal
- Oct 7
- 7 min read
Updated: Oct 28
When we open a map on our smartphone, our location is actually determined by the synchronized operation of dozens of satellites in the sky. So, what's behind the "GPS" we see on that screen? GPS (Global Positioning System) isn't just a standalone system these days. We're in the age of GNSS (Global Navigation Satellite Systems). GNSS includes multiple satellite constellations, including America's GPS, Russia's GLONASS, Europe's Galileo, and China's BeiDou, in addition to America's GPS. In other words, GPS is just one member of a vast GNSS family! Now, dozens, and in some cases, over a hundred satellites , help us determine our location, one by one. So, at this technological intersection, which one stands out: GNSS or GPS? Under what circumstances is which one more profitable? Let's explore our devices and explore the differences behind the signals coming from the sky, step by step.
Contents
The Power of Location: The Key Engineering Differences Between GNSS and GPS
GPS is a constellation of 31 satellites, initiated by the US Department of Defense in the 1970s. Today, these satellites orbit any given point on Earth with at least four visible. These four satellites enable the "trilateration" calculations needed to determine our device's three-dimensional position. Therefore, when GPS was not yet operational, quite tedious measurements were required.
GNSS , on the other hand, has taken this idea to international coordination: in addition to GPS, it accesses multiple systems, such as Russia's GLONASS with 24 satellites, the EU's Galileo, which aims to expand to 30 satellites and is nearing completion, and China's BeiDou with over 40. Thus, a single GNSS receiver can track the signals of more than 120 satellites mushrooming across the sky; it participates in a whole satellite "carnival," not just one brand.
This difference impacts the location accuracy we envision. While GPS alone typically provides an accuracy of 5-10 meters, thanks to multiple constellations, GNSS devices can easily reach an accuracy of 1-2 meters (or even centimeters in some specialized applications) . GNSS, operating on multiple satellite constellations and multiple frequencies (L1, L2, L5/E5, etc.), mitigates sources of geometric error; when one satellite shuts down, another immediately takes over. Think of this as connecting a phone to multiple channels in the sky simultaneously : instead of relying on a single signal line, it's like gathering the combined information of multiple lines. GPS, on the other hand, relies solely on the American fleet; in this respect, GNSS is much more resilient to signal interruptions or methodological limitations.
For example , a mapping device traveling to high mountains or the Arctic can maintain its position more reliably when it uses not only GPS but also GLONASS and Galileo signals. As Taoglas points out, GNSS offers uninterrupted connectivity compared to GPS alone, especially at high latitudes or in areas with poor infrastructure. While mountainous terrain or a desolate steppe can overwhelm GPS, GNSS combines redundant satellites from all systems. Therefore, while GPS may be sufficient for simple navigation in your car, GNSS is preferred for tasks requiring precision, such as surveying.
Comparison in Real Field: From Urban to Forest, From Construction to Rural
Urban Environment: Tall skyscrapers and narrow streets block GPS signals, creating multipath reflections. Building shadows can cause the GPS signal to travel long, corridor-like paths, confusing position calculations. So, what can GNSS do in this congested urban environment? It can provide a bit more convenience. For example, even if a GPS satellite isn't in line of sight, GLONASS or Galileo can be visible from another part of the sky. In other words, a GNSS receiver attempts to bypass an area shadowed by a satellite by utilizing multiple constellations simultaneously. However, even this may not be sufficient. In reality, concrete canyons in the heart of cities may still require specialized solutions (antenna positioning, 3D building models) .
Rural Areas (Open Fields/Steppes): Things are easier in fields, plains, or flatlands. When you look up in the field, you have a field of view wide enough to detect nearly dozens of satellites: the four GPS satellites are very easily detected. GNSS further enhances this. Even using GPS alone can determine your location with an error of a few meters, but multiple constellations allow you to raise the bar even higher. For example, according to Taoglas, while GNSS can achieve accuracy of up to 1-2 cm in ideal conditions outdoors, GPS alone is only within the 5-10 meter range at best. So, when collecting coordinates of a construction site's corners across a wide area, GNSS gives you a few meters more comfort. Furthermore, with network-RTK systems like TUSAGA-Aktif in Turkey, GNSS receivers can reach real-time centimeter accuracy. In open areas, a GPS device can connect to GNSS-enabled base stations to achieve even extremely high precision. Simply put, GPS alone generally works well outdoors; GNSS comes even closer to perfection with the number of spare satellites and frequency diversity.
Forested Area: The dense branches and leaves of a pine forest obscure the GPS signal, almost like a curtain. Like light from a tree canopy, the GPS signal weakens under the tree canopy. This is where the power of multiple constellations comes into play. In a recent study, the average accuracy of a smartphone using GPS alone in a densely wooded area was approximately 20 meters, while a device using GPS and GLONASS was only about 3 meters off. Two low-budget devices were tested: the single-constellation GPS device deviated significantly in the tree canopy, while the dual-constellation device performed much better. This is a prime example of why GNSS is advantageous in forested areas. Furthermore, GNSS receivers capable of accessing both GPS's L1/L2 frequencies and Galileo/BeiDou's new L5/E5 frequencies can mitigate the negative effects of reflections from trees. For example, forest engineers can achieve precise measurements even in wooded areas with a combination of GNSS and robotic total stations (CORS-GNSS). So, when working in dense tree cover, using GNSS is much more accurate than GPS.
Construction Site: Scaffolding rising into the sky, reinforced concrete steel beams, and excavators… The construction site is partly open, partly littered with scattered obstacles. GPS certainly provides the technique here, but multiple reflections of the signal (from metal components) lead to errors. GNSS, on the other hand, offers some breathing room; a wider range of satellite options makes it easier to find the right alternative, especially with signals reflected off roofs. Furthermore, civil engineers benefit from GNSS-RTK solutions. With network-RTK systems like TUSAGA in Turkey, your GNSS receiver can achieve centimeter precision in real-time on the construction site. For example, the position information obtained from GNSS-RTK allows the crew to accurately determine the exact center of the trench. As Taoglas points out, when heavy machinery in construction works with GNSS, it precisely adapts to project tolerances. In summary, while GPS provides a baseline accuracy in the construction field; For more complex work, signals that penetrate under large buildings or detailed infrastructure drawings, the use of GNSS and RTK (or DGPS) is essential.
In the table below, you can compare the preferences based on the conditions on the field:
Decisions and Conclusions
GPS and GNSS, as we understand it, serve essentially the same purpose: determining where we are on the globe. However , choosing based on the specific situation and location makes a critical difference. As a general rule, GPS may be sufficient for simple navigation and daily navigation . Your smartphone, car navigation, or basic logistics tracking will guide your "maps" with GPS. However, when high precision, challenging terrain, or industrial requirements are involved, GNSS offers a significant advantage. In mountainous terrain, the Arctic, maritime operations, or precise mapping, GNSS uses multiple satellite constellations to prevent signal dropouts.
Speaking specifically about Turkey, thanks to national GNSS networks like TUSAGA-Aktif , we can obtain centimeter-level positions across the entire country within seconds. From the Antalya coast to the Erzurum plateau, GNSS can be utilized with RTK-DGPS in any area with adequate satellite visibility. For example, on a construction site, when you identify key points with a GNSS-RTK device and mark them on the field with a picket pole, the resulting accuracy can be reduced to the level required for TÜBİTAK-supported projects. In rural areas, even GPS provides accurate tracking in wide valleys, but if you still want to ensure your location at night in a forest or against a city skyline, GNSS is preferred.
Both technologies are transforming the engineering world, but it's up to the engineer to decide which one prevails in the field . Whether on a windswept mountainside, in the shade of a city, in a dense forest, or on a dusty construction site, the abundance of satellites and frequency diversity provided by GNSS won't leave you wanting. However, for simple map drawing, GPS might be just as effective. In short, an engineer who wants to take bold steps on the map must choose the satellite network wisely based on their needs. The answer to the question of GPS or GNSS depends on where and what you want to measure at that moment.
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