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What is GNSS and how does it bring you precise positioning
Wondering how to improve your mapping project accuracy with GNSS? This powerful technology leverages signals from multiple satellite constellations to provide positioning with centimeter-level precision. So, let’s explore how GNSS can take your projects to the next level.
- What does GNSS stand for?
- What are the main satellite systems?
- How does GNSS manage to provide global coverage?
- How do you determine your exact location on Earth from GNSS signals?
- What are the factors affecting location accuracy?
- How to improve location and timing precision?
- Emlid GNSS receivers for centimeter-accurate solutions
- FAQs
What does GNSS stand for?
GNSS stands for Global Navigation Satellite Systems, which are used to determine the precise geographic coordinates of objects These systems consist of three key components: space equipment (satellites), a ground control segment for monitoring and maintaining the network, and individual receivers that process signals.
GNSS operates by measuring the distance between the receiver’s antenna and multiple satellites, whose positions are known with exceptional accuracy. GNSS ensures reliable and precise positioning, even in challenging environments by using signals from various satellite constellations, such as GPS, GLONASS, Galileo, and BeiDou.
What are the main satellite systems?
Today, different satellite systems within GNSS operate independently from each other. They were initiated by single countries or regions, with the goal of providing global or regional coverage:
| Satellite system | Country | Number of satellites |
|---|---|---|
GPS: Global Positioning System | United States | 31 satellites |
| GLONASS: Global Navigation Satellite System | Russia | 24 satellites |
| Galileo: Europe’s 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 |
The data accuracy from different constellations depends on various factors, including the quality of the receiver, environmental conditions, and the use of correction methods like RTK or PPK. Each constellation, however, also has its own inherent capabilities and accuracy limits.
How does GNSS manage to provide global coverage?
GNSS satellites orbit at a distance of 20,000 km above the Earth’s surface. A single orbit around the Earth takes about 12 hours. Providing global coverage requires a constellation of satellites, with additional ones deployed for reliability. The largest GPS constellation typically consists of 31 operational satellites.
Most modern satellite systems provide global coverage, allowing satellite signals to be received anywhere on Earth. Similarly, most GNSS receivers and antennas can recover signals from multiple satellites across multiple constellations.
How do you determine your exact location on Earth from GNSS signals?
All different components of a GNSS work together when determining one’s location on Earth:
- The satellites propagate a signal.
- A GNSS receiver and antenna receive and process a signal.
- In the GNSS RTK technique, the second GNSS receiver can be used as a base station to compare the received signal with the supposed satellite location and send corrections to the first GNSS receiver. This setup allows for centimeter-level positioning.
Signal data from at least four satellites in a single GNSS constellation can be used to measure a precise location in three dimensions (x, y, and z coordinates). This requires a line of sight between a GNSS receiver and the satellites.
GNSS receivers use the speed of light to calculate their distance to satellites by measuring the time it takes for a signal to travel from the satellite to the receiver.
GNSS signals are constantly transmitted at the speed of light and include a timestamp and the satellite’s position in orbit. A GNSS receiver has a clock synced with the satellite clock. When the signal reaches the receiver, the arrival time is recorded. By comparing the time it was sent and the time it arrived, the receiver calculates how long the signal took to travel. Since the speed of light is known, this time delay is used to measure the distance to the satellite.
To find a location on Earth, the receiver uses distances from three satellites with a method called trilateration. This method calculates your position based on the distance to three known points. However, a fourth satellite is needed to correct any inaccuracies in the receiver’s clock, which isn’t as precise as a satellite clock. This fourth signal improves accuracy, ensuring precise positioning.
What are the factors affecting location accuracy?
When a satellite signal travels through space to the Earth, it can face various factors that affect signal accuracy.
- Atmospheric conditions, including atmospheric pressure in the troposphere, result in a significant positional error.
- Signal blockage from obstructions, such as high buildings, prevents a clear line of sight to a satellite, affecting signal accuracy.
- Multipath happens when part of the signal reaches the receiver after bouncing off a surface or object.
How to improve location and timing precision?
The following three methods help improve location and timing precision, resulting in centimeter-accurate measurements:
- Real-Time kinematic (RTK) technique corrects common errors in current satellite navigation systems. The main difference between RTK and standard GNSS positioning is that RTK achieves a higher level of accuracy by using two GNSS receivers: a moving rover and a base station at a known location that provides the rover with real-time corrections. At the same time, standard GNSS positioning depends only on a single GNSS receiver that obtains satellite signals.
- Post-processing kinematic (PPK) is an alternative technique to RTK. With PPK workflow, accurate positioning doesn’t happen in real time; all algorithms are applied afterward. Both base and rover record raw GNSS logs, which are then processed in a dedicated PPK software.
Emlid GNSS receivers for centimeter-accurate solutions
Global navigation satellite systems paired with GNSS receivers and antennas enable high-accuracy applications across industries.
Emlid’s GNSS receivers track signals from multiple GNSS constellations, including GPS, GLONASS, BeiDou, Galileo, and QZSS and ensure reliable performance even in challenging environments. Designed for RTK, PPK, and PPP surveying, Emlid Reach receivers can be used for precise surveying, drone mapping, and GIS applications.
Tim Durham’s recent drone mapping project demonstrates how Emlid’s GNSS receivers help to achieve accurate drone mapping results. To create a 3D model of an old barn scheduled for demolition, Tim used a Reach RS2+ base to stream RTK corrections to his DJI RTK drone (used as a rover). This allowed Tim to capture precisely located aerial data, which he then processed using photogrammetry software to create an accurate 3D model.
Ready to achieve centimeter precision in your projects? Explore Emlid’s GNSS receivers and elevate your surveying, mapping, and GIS workflows with precision and reliability.
FAQs
What is the difference between GPS and GNSS?
GPS (Global Positioning System) is a specific satellite navigation system operated by the United States. While GNSS (Global Navigation Satellite System) is a broader term that includes multiple satellite systems such as GPS, GLONASS (Russia), Galileo (Europe), and BeiDou (China). GNSS can utilize signals from multiple constellations, offering better accuracy and reliability than single GPS, which relies solely on its own network.
How many GPS satellites are there?
The GPS constellation typically consists of 31 operational satellites. These satellites work together to provide precise positioning, navigation, and timing services worldwide.
How accurate is GNSS positioning?
Standard GNSS positioning can provide accuracy within several meters. Advanced techniques like RTK (real-time kinematic) and PPK (post-processing kinematic), supported by Emlid GNSS receivers, enhance this to centimeter-level precision.
How do Emlid receivers help mitigate GNSS inaccuracies?
Emlid receivers use advanced correction methods, such as RTK and PPK, to counter common issues affecting GNSS accuracy. They also support multi-constellation tracking, which ensures reliable signals even in challenging environments.
Can I use GNSS receivers for drone mapping?
Yes! Emlid GNSS receivers are ideal for drone mapping. When used as a base station for an RTK/PPK drone, the Emlid Reach receiver enables precise image geotagging and supports workflows such as creating orthophotos and 3D models.