What is GNSS? A Beginner’s Guide

In this article we will cover the basic principles behind GNSS positioning and GNSS corrections. For a technical overview of GNSS technology, refer to our blog What is GNSS Positioning?

What is GNSS?

Global Navigation Satellite Systems (GNSS) refers to any satellite constellation that provides global positioning, navigation, and timing services. The most well-known systems include the United States' GPS, Russia's GLONASS, the EU's Galileo, and China's BeiDou. 

How does GNSS work?

GNSS satellites orbit the earth transmitting coded signals containing two pieces of information: where they are in orbit and a stable timestamp from an onboard atomic clock. The time it takes for a signal to reach a GNSS receiver on Earth (the one in your cellphone or car, for example) lets it know how far it is from the satellite. To determine its position, the receiver needs to collect information from a minimum of four satellites. When the receiver knows the precise position of itself with respect to each satellite, it translates its own position into a three dimensional Earth-based coordinate system.

How accurate is GNSS?

Standard GNSS receivers achieve an accuracy of 5 to 10 meters in an outdoor environment.

What causes GNSS errors?

GNSS systems are susceptible to various sources of errors that degrade the accuracy of positioning solutions. The largest source of error is caused by the Earth’s atmosphere as GNSS signals are slowed down and refracted as they pass through the ionosphere (outer layer) and troposphere (layer near the Earth’s surface). While very precise, atomic clocks onboard GNSS satellites are susceptible to slight deviations that affect the receiver’s calculated position. Similarly, satellite orbits can also deviate slightly from their documented paths. Lastly, in complex environments, GNSS receivers receive multiple copies of the same signal as it bounces off nearby objects such as buildings and trees, affecting its location calculation. These errors compound to an overall positioning error that ranges between 5 to 10 meters.

What are GNSS corrections?

GNSS corrections improve the accuracy, integrity, and reliability of positioning information obtained from GNSS systems by accounting for the various errors and applying them to the satellite signal being received on the ground, improving accuracy from 5-10 meters down to 2 cm. 

How do GNSS corrections work?

GNSS corrections typically rely on a single base station, or a network of Continuously Operating Reference Stations (CORS) which consist of high-quality GNSS receivers that continuously collect satellite data. Each station compares the observed satellite data with its known fixed position, thereby inferring the errors that also affect all receivers in its vicinity. Different correction methods employ various algorithms to determine what corrections to transmit to receivers in the field, which apply these to their own raw positioning data.

What types of applications require GNSS corrections?

GNSS corrections are an essential prerequisite in any application requiring precise positioning. 

Autonomous vehicles: GNSS corrections are a crucial sensor for safe navigation of self-driving cars and ADAS. Read our blog post to learn more about enhancing automotive safety through precision GNSS. 

Outdoor robotics: GNSS corrections improve robot safety, navigation and enable features such as virtual geofencing which is essential in use cases such as robotic lawn mowers. Read our blog post to learn how we test the accuracy of GNSS solutions for outdoor robots.

Construction and utilities: GNSS corrections enable precise measurements of land and buildings which is important for accurate and safe construction planning. When mapping utilities, corrections are vital for safely locating and recording underground pipes and cables which prevents future damage and streamlines maintenance callouts. Read our case study to learn how Deutsche Telekom uses precise positioning to quickly and safely lay its fiber optics infrastructure.

GIS mapping: GNSS corrections bring affordable survey-grade precision to GIS processes such as utility pole mapping and urban vegetation management. Read our blog post to learn how to choose a precise positioning solution for your GIS project.

Delivery systems: With GNSS corrections, logistics companies can improve route optimization with lane-level navigation, ensuring accurate and timely delivery to the correct address. It also enables autonomous delivery via robots and drones with safe and precise navigation.