How do these things work??

EKRIUQ

How do these things work??, not the console but,

1) If I buy one for my car is it a case of taking it out of the box and placing it on the dash or does it have to be installed by a professional installer.

2) Are they easily transfered from one vehicle to another.

3) Now if I get past the install stage How does it work, Is it being connected to a satelite in the sky than can pinpoint my exact location and thus knowing when to tell me when to take turns etc..

Thanks for just clearing up these things before I purchase:)

robinph

BingoBongo wrote:

1) If I buy one for my car is it a case of taking it out of the box and placing it on the dash or does it have to be installed by a professional installer.

Buy it, take it out of box, use suction cup thing and attach it to windscreen or dash, press the on button.

BingoBongo wrote:

2) Are they easily transfered from one vehicle to another.

Yep, just remmeber to never leave it behind in the vehicle, or the holder attached to the dash which would then suggest to a thief that you might have "hidden" it in the glove box.

BingoBongo wrote:

3) Now if I get past the install stage How does it work, Is it being connected to a satelite in the sky than can pinpoint my exact location and thus knowing when to tell me when to take turns etc..

There are a load of satelites, about 30ish I think in total, that it will connect to for it to determine your location. It needs to be able to see at least 4 to get a good fix on your location but the more it can see the more accurate it will be down to nearly +/- 3 meters, I'm generally getting a claimed accuracy of about +/- 8 meters around Dublin as the surrounding buildings will affect the quality of the signals that it can get from the satellites. What is more important though is the quality of the maps that the unit will come with though as knowing your longtitude and lattitude is not much use to you without the map in the unit as well, some unit have pretty poor maps of Ireland outside of the major cities though so you should check out the maps for your area on any unit.

EKRIUQ

Thank you robinph for that information:)

Positive rep points

Krusty_Clown

A GPS receiver doesn't actually connect to a satellite. I'm not trying to be picky, it's just that many people get confused with how GPS receivers actually work, and the analogy that they connect doesn't help matters.

What happens is that you have satellites orbiting the earth (around 2.5k of them, of which as robinph points out, 24 are used to provide GPS data). At any time, your GPS receiver (in theory) can see at least six of these satellites. Each of thesesatellites is broadcasting data, which is picked up by your receiver. So each of the satellites are sending something similar to a timestamp. Your GPS receiver compares the satellites timestamp, to it's own clock (this is a gross over-simplification!) and uses the difference to calculate how far away the particular satellite is. When it calculates its distance from three or more satellites, it can use a form of triangulation, to figure out exactly where on the earth's surface you are (and even make educated guesses at your altitude on the earths surface). So, what does this mean (and some common mis-conceptions):

1) There is no subscription service for GPS. Your device is just reading information that is broadcasted by satellites (like a radio picking up radio signals)
2) Data is only communicated in one direction (i.e. your GPS receiver receives data - it does not / cannot send data. The government can't track you (unless it's a purpose built GPS device that has something like GPRS transmission)
3) There is no expensive/complicated wiring etc.. It'll work anywhere (of course it needs power of some sort) as long as it can receive data from three or more satellites (Don't expect it to work too well indoors). Things get a little more complicated if you want to have it hard-wired into your stereo system etc.. Many come with their own speaker and are powered by your cigarette lighter socket.
4) As robinph pointed out, knowing when to turn left and right depends on the devices maps. The satellites don't know where you are.
5) It can also use this satellite data to establish useful information, like speed, distance, routing etc.

Battlejuice

That was a brilliant explanation Krusty_Clown!
Have got hold of a Forerunner Garmin 305 GPS for outdoor activities and it's functionality seems a little extra-terrestrial to me. Do you know where I could get any more detailed information online (been trawling through the net for a 'dummies' explanation that is also concise but haven't had much luck so far).
I was told that a new system will be launched with the GPS being able to measure coordinates to 1 metre accuracy. Probably just a rumour though.

robinph

A GPS for dummies explanation would be pretty hard to do I expect and we just have to accept that us mere mortals are not meant to fully understand such things.

The page on the ever reliable Wikipedia goes into a bit more detail, but I'm still not able to get my head round some of the explanation there and I suspect that the people writing that page don't know themselves. The "triangulation" to the satelites is made that much more difficult buy the fact that none of them are in stationary orbits* and the atomic clocks on board run at a different speed to those on the ground becasue of that Einstein fellow and one of his theorys. The accuracy is still more limted by what the US government wants to allow though, and their recivers will be better than anything we can get.

*There are actually a couple of geo-stationary satelites up now that improve acuracy a bit further by correcting the GPS, but those ones are only visible from the US yet. WAAS

Sundy

Battlejuice wrote:

I was told that a new system will be launched with the GPS being able to measure coordinates to 1 metre accuracy. Probably just a rumour though.

With survey grade GPS you can get better an accuracy of .020m or less, depends on post processing etc. So sub 1 metre is nothing really. But then you dont put 10 grand worth of equipment in your car, so i guess accuracy is related to cost.

Krusty_Clown

How stuff works is always a useful resource for getting your head around electronics, machinery etc.. Here's their GPS article: How GPS Receivers work

The forerunner is a nice piece of kit.. I usually drive my running routes with my GPS first, to get an idea of distances, elevations etc.. (You can plot the elevation profiles using a website like: www.gpsvisualizer.com).. Here's my current training route for the Connemarathon.

The technology you're referring to is EGNOS (European Geostationary Navigation Overlay Service) and consists of three satellites and a load of ground based transmission stations (which transmit error correction data to the satellites, which then fire it back to you GPS receiver). Thankfully, most modern GPS receivers are already equipped to receive WAAS (US) and EGNOS (Europe) data. If your GPS receiver can receive data from these EGNOS satellites (based on your/their location) then you should be able to use EGNOS already.

You can give it a try by enabling WAAS or EGNOS in the GPS menu of your receiver (if you're using a Garmin receiver, you should get a 'D' beside any satellites from which you are receiving EGNOS/WAAS data, on the GPS Info screen). The 'D' is short for differential.

Supposedly though, the disadvantages currently outweigh the benefits, as (and this may not be 100% accurate, as I'm recalling this from memory!):
1) You may not be able to pick up any of the differential satellites.
2) Enabling WAAS takes up a couple of satellite channels which would otherwise be available for reception of regular GPS satellite data, which could affect your accuracy (typically 2 of 12 channels).
3) Has an impact on the processing power of your GPS receiver (probably a moot argument with more modern GPS receivers).
4) Most people don't actually need 1 metre accuracy (typical users).

Of course, if you plan on doing something like Geo-caching where acurracy is very important, and you can receive these signals, then you should enable it. But on the road, where most receivers use road-lock anyway, and the maps aren't accurate to 1 metre, then it's overkill.

Here's more info on Egnos, WAAS, and MSAS.

JHMEG

WAAS is US only.. there is no coverage here. EGNOS is not operational, and no satnav devices can receive it anyway.

OSI have a series of earth-based stations dotted around the country that improve on GPS accuracy. These are proprietry however, but are free for anyone to use (someone mentioned survey grade).

Krusty_Clown

JHMEG wrote:

WAAS is US only..

I thought that was clear from my post. Maybe you didn't read it?

JHMEG wrote:

EGNOS is not operational, and no satnav devices can receive it anyway.

The system started its initial operations in July 2005, showing outstanding performances in terms of accuracy (less than 2 metres) and availability (above 99%); it is intended to be certified for use in safety of life applications in 2008.

and, direct from the European Space Agency's website:

EGNOS wrote:

Since July 2006 the operational EGNOS signal broadcast on PRN126 and PRN120, is using the MT0/2 and Band 9 of the Ionospoheric grid.

You do need line of sight, but I mentioned that already.

JHMEG wrote:

...and no satnav devices can receive it anyway.

Finally, all recent GPS receivers are equipped to receive both WAAS and EGNOS signals. Here's a really old list (again from European Satellite Agency's EGNOS website) of supported devices:
http://www.egnos-pro.esa.int/SBAS_receivers.pdf
Needless to say, all more recent devices from these manufacturers also include this support..


Maybe you're getting confused with Galileo?

JHMEG

Krusty_Clown wrote:

I thought that was clear from my post. Maybe you didn't read it?

I did.

Krusty_Clown wrote:

The system started its initial operations in July 2005.. it is intended to be certified for use in safety of life applications in 2008.
Finally, all recent GPS receivers are equipped to receive both WAAS and EGNOS signals.

Maybe I should have said that while most current receivers can receive EGNOS, support is turned off by default and cannot be enabled. EGNOS is still in test and is not considered live.

Krusty_Clown wrote:

Maybe you're getting confused with Galileo?

No, I'm not.

Krusty_Clown

JHMEG wrote:

Maybe I should have said that while most current receivers can receive EGNOS, support is turned off by default and cannot be enabled.

The attached screenshot is from my old Garmin Quest...
Maybe non-Garmin devices don't have this support included?