GLONASS is Russia’s version of America’s GPS. It is used to tell electronic devices where you are.
“GPS” specifically refers to the American system of navigational satellites rather than generic satellite navigation. We all use the term ‘GPS’ incorrectly in that sense.
GLONASS capability is increasingly used in high-end SMART devices, including the new Garmin Fenix 5 and Suunto SPARTAN.
GLONASS is neither particularly better nor worse than GPS.
HOWEVER, when they are used TOGETHER the likelihood of accuracy *IS* increased. Simply because there are more satellites available in both ‘constellations’ and hence a higher chance that your watch will be able to see enough of them for a good positional fix.
It is said that using GPS+GLONASS can give accuracy down to 4.5/5m and can also improve accuracy in built-up areas; especially in the Northern Hemishpere.
Downsides: None really. Might use a tad more battery power though depending on how well the watch manufacturer has optimised the navigational chip inside the device. Well…I say “none really” but, in my experience, turning on GLONASS does take a big hit on battery.
Do I really need it? It will help with tree cover and nearby tall buildings. It may also help in mountainous areas or areas of high latitude (nearer to Arctic circle). I would say “It shouldn’t hurt” but, from my experience, occasionally it does NOT SEEM to improve positional tracking
Don’t be fooled: Just because a device is advertised to have GLONASS doesn’t mean that much for the ACTUAL level of accuracy you will receive. There are VERY MANY OTHER factors that will affect this such as: quality of GPS/GLONASS chip; position of antennae; electromagnetic shielding within the device; algorithm used by the manufacturer of the end device. Indeed anecdotal evidence is that sometimes GLONASS might lower accuracy. Why? One of the factors is the quality of the manufacturer’s algorithm might be sub-par.
ESSENTIAL READING: (Here) are my GPS/GLONASS tests on sports watches – as of 11Feb 2017 best performers so far are: TomTom Adventurer/Spark/Runner 3; Suunto SPARTAN Sport (not ULTRA); and Garmin’s Fenix 3.
Future: Europe’s Galileo system will come into action around 2020. Many chips currently enabled with GPS and GLONASS also support Galileo. GREATLY increased accuracy is hopefully going to happen then with 1m accuracy. HOWEVER my suspicion is that there will be an increased USER-cost associated with obtaining the 1m accuracy of Galileo and hence the extra accuracy may not be passed on to you or, if it is, you may well be charged more for it. Thus, for most of us, Galileo may well make no difference other than, like GLONASS, giving more satellites for us to see and get a higher chance of achieving the 4.5/5m accuracy that we should have had all along!
FWIW I *DO* have it ‘always on’ on the devices that I have that support it. I only turn it off on the rare occasion where I am doing a long exercise that might be battery dependent.
SUMMARY: It’s a nice-to-have for most people that will make little difference.
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