What is GNSS?
GNSS and GPS are often used as interchangeable terms. Almost everyone thinks they know what GPS is, “it’s satnav, right?”. This leads to my standard answer, “yes… and no”.
GNSS stands for “Global Navigation Satellite System”, GPS for “Global Positioning System”. This doesn’t sound like a big difference. However, GPS is American owned and operated, and is an example of what is known as a GNSS constellation. Following? Essentially, it’s like Hoover. Hoover has become a colloquial term for a vacuum cleaner, despite being a brand name. The same is true for lots of things like Jacuzzi, Kleenex (in the US atleast), or iPad to name but a few.
There are four main GNSS constellations. GPS, GLONASS, Galileo, and BeiDou. As mentioned, GPS is American owned and operated. GLONASS is Russian, Galileo is European, and BeiDou is Chinese. Use of each constellation is therefore dependant on where you are in the world. The other major consideration is the initial purpose of these constellations. GPS and GLONASS where established primarily for military use during the Cold War, so their focus is slightly different to Galileo. We get a good basis for where these satellites are focussed based on who built them. Galileo is an EU constellation made as a collaboration between multiple member states, and is therefore designed primarily for those nations, and focuses more on the Europe region. GPS focuses on America and American “strategic locations”, GLONASS on Russia and Russian “strategic locations”. The same theme is true for BeiDou and China.
So, why does this matter? Basically, if you buy a receiver with just GPS, you’re limited to signals from that constellation of satellites. Most receivers can use any number of satellites, by using just one system you are limited to 24 satellites. Each constellation’s focus also matters. GLONASS has must better coverage in the Northern limits, whilst BeiDou covers Asia with greater consistency. In the UK, GLONASS and increasingly Galileo are the most useful constellations.
Of course, all four constellations face the same issues regarding line of sight and atmospheric conditions.