GNSS has become a crucial part of our lives from everyday consumer tools such as navigation apps and fitness tracking, to highly specialized industries such as transportation, agriculture, construction, mining, utilities, military, and emergency services. So, what is GNSS and how does Juniper Systems Geode GNSS Receiver work for you?
GNSS stands for Global Navigation Satellite System, providing positioning, navigation, and timing (PNT) information anywhere on earth with a clear line of sight to multiple satellites. The Geode GNSS Receiver is a simple one-button design that receives GNSS data to deliver sub-meter, sub-foot, decimeter, and centimeter accuracy options.
How It Works
There are three parts to a GNSS location: constellation of satellites, a model of the shape and size of the Earth and a portable/moveable GNSS receiver. These three elements work together to determine a location. The precision and accuracy of the location is affected by many factors. To get the most precise and accurate data from the Geode, consider the following factors.
The Satellite Relationship
In days of old, sailors would use the observation of stars in the sky to determine their location at sea. GNSS satellites operate as “artificial stars” by transmitting highly accurate timing signals from known locations in space. GNSS satellites transmit using specific radio frequencies. The better the Geode receives data from the satellite(s) the more precise and accurate your location can be. For the best performance, consider the following:
Line of sight
The Geode must have a clear line of sight to satellites to function most effectively. Operating your Geode inside a building may work, but not optimally. Similarly, if there are large trees or buildings between the Geode and the satellite(s), the signal will not be as strong or clear as it could be without the obstructions and may provide a less accurate position. The Geode is capable of receiving many satellites from multiple GNSS constellations which can help to reduce the effect of nearby obstructions.
Atmosphere
Since the signal from the satellite(s) to the Geode moves through the air, it is affected by earth’s atmosphere and solar events. Unfortunately, there isn’t much that can be done to minimize the disruptions from solar events. In general, signals from multiple satellites can provide reliable location data despite the uncontrollable nature of air and space. (SBAS correction services are designed to detect and mathematically correct atmospheric disruptions.)
Corrections
There are a variety of mathematical approaches to create the most precise location data possible. These function in different ways and mitigate various possible errors or inconsistencies. (See the Augmentation section below.)
Satellite constellations
GNSS Satellites are put into space by various countries and companies. They travel around the earth in different ways. Not all satellites providing GNSS signals are available to your Geode at all times. The position and availability of a signal from the various satellite constellations may affect some settings and choices using your Geode.
| Satellite Constellation | Owner |
| GPS | US |
| GLONASS | Russia |
| GALILEO | European Union |
| BeiDou | China |
The Map Model
The geode delivers data based on a model of the Earth, and a coordinate system, latitude and longitude. Together these are represented as a coordinate reference system (CRS). These reference systems can vary depending on the correction service used with the Geode.
Representing a three-dimensional globe
It is challenging to create a flat map of a rounded surface. The precise location combines the map projection (a digital display of a flattened shape representing the 3D earth) with coordinates (latitude, longitude) to create your location. Depending on how you use the collected data you may prefer one type of map projection over another.
GNSS systems use the WGS84 model of the Earth (EPSG 4326), and the Geode uses this to output data in latitude and longitude. When maps are displayed in an application, this is often converted to a new projection, (EPSG 3857) to make the maps look smooth and seamless when you scroll or zoom out. The Geode will deliver data in different reference systems, based on the correction being applied (see Augmentation, below).
Elevation
If you need precise elevation data along with location coordinates, make sure you know your Geode’s height above ground, and use the same starting reference point, like sea level, for all measurements. If very accurate elevation is essential, you might want to use a geoid model for even better precision. Details on setting up geoids default can be found in Conversion Tools for Transforming Geode Data and specific instructions on how to install and select a specific geoid when using them in Uinta are available in Uinta- Coordinate Reference Systems.
Plate Tectonics
Even though the ground feels solid, it is slowly moving due to plate tectonics. Some coordinate systems account for these movements to improve accuracy.
Augmentation
To improve accuracy, the Geode uses mathematical adjustments called “corrections” from different services. These adjustments help ensure accurate real-time positions, even in rough environments with limited satellite visibility.
Here is a brief overview of augmentation services used by the Geode.
| Augmentation Type | Details | |
| SBAS | Differential Correction | SBAS (Satellite-Based Augmentation System): What: SBAS improves GNSS accuracy by broadcasting corrections for signal errors (ionospheric delay) and signal integrity information. How: It uses fixed ground reference points to monitor and correct GNSS signals within a specific region. Corrections are sent via geostationary satellites to users. Examples of SBAS services include WAAS, EGNOS, MSAS, and GAGAN. For further details, see Geode User Manual, Section 2.3.1. |
| NTRIP | Delivery method that makes networks of localized base stations possible. | NTRIP (Networked Transport of RTCM via Internet Protocol): What: A protocol to deliver GNSS corrections over the internet for RTK (Real-Time Kinematic) and CORS (Continuously Operating Reference Stations). How: The Geode device accesses RTK/CORS corrections via internet or cellular data, providing high-precision locations (centimeter-level) using an NTRIP subscription and a stable internet connection. |
| Atlas | Correction Service | Atlas Correction Service: What: Satellite-based GNSS corrections with higher-level accuracy that corrects for several sources of signal error. How: Atlas uses multiple satellites to deliver corrections for areas up to 75° latitude. These services require a subscription. |
In conclusion, maximizing the performance of your GNSS receiver comes down understanding its relationship with satellites and with the earth. Remember, GNSS technology is rapidly advancing, so keeping up with new developments can help you leverage even greater accuracy and reliability over time. By following these tips and refining your understanding of GNSS data, you’ll be well-equipped to get the most accurate, dependable results, no matter where your work or adventures take you.
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NOTES
From <https://www.u-blox.com/en/technologies/what-is-ntrip>
NTRIP is a messaging protocol based on HTTP and used for streaming GNSS corrections data over the internet for real time kinematic positioning, commonly referred to as RTK. NTRIP is the messaging format or the ‘packaging’ around the message being sent. RTCM is a standardized data format used to ‘structure’ the message itself. NTRIP protocol is typically used in combination with RTCM.