How does GPS work?

[jorgemartin]

Hello,

I'm planning a trip to Russia and Mongolia and I'd be interested in knowing how GPS works. I'm not saying I'll use it, I'd like to know how it works so I can make an informed decision. Does GPS work in these countries? What kind of device should I use? Does software need to be downloaded? Are there GPS maps for these countries? In a nutshell, I don't know anything about GPS and I'd very thankful if someone could help me understand it and its relevance to a cycling trip in these parts of the world. Many thanks!

 

[Bman]

Basically, GPS' (Global Positioning Systems) use satellites to work out the position on the surface.

Once the position is worked out, some GPS systems have maps and other features to enable you to navigate.

Yes, it will work everywhere in the world.
The kind of device you need depends on what you want it to do.
Some devices do need extra maps to be downloded.
Im pretty sure you can find any map you need.

I use a Garmin Edge 305. All that does is record my position, speed etc. So I can upload the data to my pc and see it on a map. I could set waypoints and routes to follow, but it doesnt have mapping functionality as such.

A Satnav is a little different. It uses GPS to track your position, and uses downloaded maps to allow you to navigate to your destination (turn left in 300 yards, etc).

More info here: http://en.wikipedia.org/wiki/Gps

 

[ColinJ]

Hello,

I'm planning a trip to Russia and Mongolia and I'd be interested in knowing how GPS works. I'm not saying I'll use it, I'd like to know how it works so I can make an informed decision. Does GPS work in these countries? What kind of device should I use? Does software need to be downloaded? Are there GPS maps for these countries? In a nutshell, I don't know anything about GPS and I'd very thankful if someone could help me understand it and its relevance to a cycling trip in these parts of the world. Many thanks!

GPS works using the signals from a network of satellites that the US government kindly put into orbit for that purpose. The original use was to allow the US military to know exactly where they were when they were going out to knock nasty people's huts down or to protect the local opium crop.

Fortunately, the technology has now filtered down to the rest of us and jolly useful it is too! As long as a GPS unit can lock onto the signals from 3 satellites you can get an accurate positional reading.

If at least one extra satellite is in clear view then an accurate elevation reading can be determined too.

Usually there are plenty of satellites in the visible sky but there will be times when there aren't. If you are in a narrow, deep-sided gorge for example the view of the sky for both you and a GPS unit will be limited. That probably wouldn't be a huge problem because you wouldn't have a huge choice of routes to worry about, maybe just one road along the bottom.

Heavily forested roads might present a more serious problem. The signals from the satellites are very weak so it doesn't take much to block them. Older GPS units certainly lost signal-lock under heavy tree cover. I've heard that more modern units can cope better but I'd assume that there might still be problems.

Like any other piece of technology, GPS units can pack up. Mine has been totally reliable, but I always carry a paper map just-in-case.

Some GPS units don't have built-in mapping - my bottom-of-range Garmin Etrex for instance. I have the mapping software installed on my PC and plot routes on that which I then upload to the GPS. It presents me with a 'breadcrumb trail' to follow on the GPS screen. I can see when turns are coming up and am ready for them.

More expensive GPS units have mapping facilities built in. You can buy mapping software to install on such a device. The coverage for places like europe and north America is very good but I'd hazard a guess that Russia and Mongolia are not going to have decent mapping software available. I could be wrong but if you go on Google maps, you won't find many roads away from big Russian cities. Of course that might be because there aren't many roads in such places!

The thing is - my simple GPS can be set to give a very accurate grid reference (it can cater for several different formats including the OS national grid). If you had accurate paper maps for where you are going then a GPS would let you work out where you are at any given time. You could navigate by maps and double-check your location using a GPS.

Sounds like a great trip - enjoy it!

 

[HJ]

For the full answer see here...

As so bear in mind that, should it choose to, the US government can turn it off without notice.

 

[jorgemartin]

Thanks everyone for your replies! The mysterious world of GPS is becoming comprehensible! Another question... If I get a basic device (such as the Garmin Edge 500) to provide me with a reference, how do I use that reference to track my location on a paper map (such as map of Russia or Mongolia)? Cheers

 

[andym]

As so bear in mind that, should it choose to, the US government can turn it off without notice.

on a scale of likeliness that's about as likely as the Pope deciding that god probably doesn't exist after all and the catholic church should jack it in...

Going back to the original questions: there are lots of different ways to use a GPS ranging from blindly following turn-by-turn directions (not advisable) to only using it in extremis to give you a grid reference on a paper map.

If you get a Garmin GPS with built-in mapping then it will come with some basic mapping which should show at least major roads. If you want something more detailed - it could be more difficult, especially if you want topography, or off-road tracks. It's worth researching and there's a good chance there will be something for Russia - Mongolia could be a bit more difficult.

I think they're worth having - if only as an emergency 'where-the-heck-am-I' device.

My personal recommendation would be something like a Garmin Legend HCx or a secondhand monochrome Legend. I'm sceptical about GPSes that are allegedly 'bike-specific' as this usually means they are designed as training aids - and so not necessarily the best devices for the touring cyclist.

 

[Norm]

The problem with the requirements of the OP are that he would be looking for maps to cover Russia / Mongolia. If available, to cover that much area, the files would be simply enormous!

Are there any GPS units which have maps to cover that area and would Jorge be able to store them all on a few memory cards? I don't think that stopping to link with a PC to download new maps would be a good solution.

A quick search through the Garmin site, for instance, carries a link to a third party developer's site here, but it's all in Russian, so I can't even see what size the maps are.

Without electronic maps for your GPS, you'd be better off looking at it as a "where am I?" device to use with paper maps.

 

[ColinJ]

As so bear in mind that, should it choose to, the US government can turn it off without notice.

True, but there would be a huge international uproar if the USA went back on their policy:

U.S. policy was expanded in 2004 in response to changing international conditions and the incredible growth in the types and complexities of GPS applications. This policy reaffirms the United States commitment to provide reliable civil space-based positioning, navigation, and timing services through GPS on a continuous, worldwide basis -- freely available to all. The policy also calls for improving the performance of GPS and cooperating with other nations.

I can set my Etrex to display Latitude/Longitude. You can locate your position to within 5-20 metres which should be accurate enough for any bike ride I'd ever contemplate!

The big question is - is it actually possible to get hold of accurate paper maps for the wilds of Russia and Mongolia?

 

[psmiffy]

At present there is a European GPS system being deployed - to be good enough for safety critical uses in aviation -not all there yet - as usual funding , cost overuns etc

One of the things that you should note about GPS is that it does not calculate position on the earths surface - but rather on a theoretical speroid and converts it to the appropriate map projection - so always for best accuracy make sure that the mapping datum you are using is set correctly on your GPS -

In various parts of europe that I have cycled in I have forgoten on occasion with the result that my track has been in the sea

 

[psmiffy]

The big question is - is it actually possible to get hold of accurate paper maps for the wilds of Russia and Mongolia?

They exist but at present the people that own them would prefer that you use the local equivalant of the AA atlas

 

[andym]

The problem with the requirements of the OP are that he would be looking for maps to cover Russia / Mongolia. If available, to cover that much area, the files would be simply enormous!

It depends a bit on your definition of 'enormous' - a 2gb memory card isn't hugely expensive and would hold an awful lot of data. (If you get a GPS that takes SDHC cards then you can go up to 4Gb or more) So the major problem is finding the mapping.

 

[Norm]

I was basing it on TomTom's European maps being nearly 2gb alone.

Western & Central Europe 2GB v8.45
Download 1724.6 MB

Detailed map seamlessly covering Western and Central Europe - modified to fit devices with 2GB memory.
Map coverage statistics:

• countries fully covered (99.9%): Andorra, Austria, Belgium, Czech Republic, Denmark, Estonia, Finland, France, Germany, Great Britain, Italy, Liechtenstein, Lithuania, Luxembourg, Hungary, Malta, Monaco, Norway, Poland, Portugal, San Marino, Slovakia, Slovenia, Spain, Sweden, Switzerland, the Republic of Ireland, the Netherlands, the Canary Islands and the Vatican City.
• countries partially covered: Bulgaria (54%), Latvia (63%) and Croatia (42%, including major cities and coastal areas)
• roads covered (kms): over 8.7 million
• connector roads: other Central European Countries and Russia are covered by a connector network of major roads that allows you seamless navigation throughout the entire region.

On reflection, though, I guess the road network is pretty patchy out east so there won't be as much information on the cards as there is in most of Western Europe. So, yes, if you could find the maps, you could probably get it all onto a 4gb card.

 

[jorgemartin]

Thanks again everyone! I think I'll go for a very simple GPS device such as the Garmin eTrex H and get decent paper maps. Also... doing a bit of research it looks as if bringing GPS devices into Russia might be a problem. Anyone had any experience of this?

 

[psmiffy]

I met several cyclists in Estonia who had cycled from Russia and had GPS on their handlebars- must be able to do it - or maybe they just did not admit to it - sorry not very helpfull

 

[samid]

To the OP: Garmin road maps for Russia seem to be available from Garmin.ru: http://garmin.ru/products/maps/790/ (that page is in Russian - I can translate the critical bits for you if you like, send me a PM). I really doubt that GPS units are forbidden in Russia.

As for the size of the maps - I don't think it should be a problem loading all of Russia's and Mongolia's roads onto a 2GB card as fortunately there are almost no roads in Russia (and that's almost not a joke). My guess is the situation is similar in Mongolia. All of UK's roads (from Garmin Europe maps) take up only about 200Mb - so, 2GB should be more than enough for Russia and Mongolia.

FWIW - I have been using a Garmin Vista HCx for a few years and am pretty satisfied with the unit. A big plus for touring versus bike-specific units is using AA cells rather than some special rechargeables. It also has turn-by-turn navigation - IME, quite usable providing you understand its limitations.