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Global Navigation Satellite Systems (GNSS) is the generic term for a group ("constellation") of satellites that send out radio signals which help a receiver to find its position.
The American Global Position System (GPS) was the first of these but there are now four constellations of navigation satellites, each covering the whole of the Earth - GPS, the Russian Glonass, the Chinese BeiDou and the European Union's Galileo. Some satellites from these constellations should be visible from any point on the Earth's surface with a clear view of the sky. There are other constellations that cover limited areas of the planet.
Greg Milner's book "Pinpoint – How GPS is Changing Technology, Culture, and Our Minds" (pub Granta 2016) is a very readable history of the GPS system.
To find its position, a GNSS receiver must receive at least one signal each from four satellites. Receivers are available that can use the data from any or all of the constellations to find their position.
I have a GNSS receiver in my garden shed. As I write, it has just received:
One use of a GNSS receiver is well-known. A Satellite Navigation (SatNav) system contains a GNSS Receiver, a digital map stored using some sort of Graphical Information System (GIS) and a sophisticated piece of software that keeps track of where the device is and figures out a good route from there to wherever its user wants to get to. SatNavs have been used by drivers, sailors and pedestrians for many years and nowadays the technology is built into smartphones.
Other types of GNSS receiver are used just to find the device's current position. These are used for applications such as land surveying.
A single GNSS device can find its position to within about three metres. That's adequate for a SatNav but land surveying needs more accuracy. Using extra equipment, two or three centimetre accuracy is typical and millimetre accuracy is possible.
Survey-grade GNSS devices have been around since the 1990s. They used to be very expensive and initially only large organisations could afford to use them. The UK's mapping authority the Ordnance Survey was an early adopter. Ordnance Survey maps have been based on GNSS surveys for twenty years or more.
Over the last few years, prices have fallen dramatically and now (in 2024) centimetre-accurate GNSS devices are available for a few hundred dollars, making it feasible for a local architect, a builder or an individual enthusiast like me to buy them.
They can be used for all sorts of purposes. I'm working on a proposal whereby young people (aged eleven to eighteen years) will use accurate GNSS receivers to measure the effects of continental drift.
Although the equipment is now cheap, it can be quite difficult to figure out how to use it properly. Fixing that is one of the purposes of this website.
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