GPS signal Offshore

"Add you need do is drive somewhere there is no cell service (In in North American west or Australia this is not hard), and use the GPS to drop a pin on your blank map. Then drive back to cell service area and see that the pin is exactly where you were."



er..... wut?


A true gps device does not need cell towers or wifi for a fix. The iphone is not a stand alone gps.

where the iPhone falls short in the GPS department is it's power. The iPhone has to share it's available power with so many other functions or receivers while true GPS devices A) do not share power or B) have way more available power I.E. 12 volt car electrical system. Sad to say but the iPhone is a weak and girly GPS device. Though if you turn your wifi and Bluetooth off itcan be amazingly accurate.

The iPhone doesn't need a wi-fi or cell connection to get a fix either. It needs a wi-fi or cell signal to load Google Maps data. This has nothing to do with the hardware, it is simply the way Google Maps works. iPhone is perfectly capable of storing maps data in the phone's flash memory.

In what way is it weak and girly?

You're comparing the device to sat sav systems, which is like comparing apples to oranges. If and when the iPhone gets a proper sat nav app, and I can see no reason why it is not capable of running one, it would then be a fair comparison.

And surely the power issue you mention is easily resolved by getting a car charger?

Your choice of pejoratives (girly) reveals more about you than about iPhone.

Make sure you turn off 3G, since that seems to confuse it when getting a first fix.

Also make sure the time and timezone are correct.

Then leave it on for at least 15 minutes.

In your case, make sure it's got a clear view from above you, down towards the South. (There are no GPS satellites orbiting north of the North Sea.)

The iPhone GPS system can only locate you up to 30 feet of your actual position. Dedicated GPS systems can locate you up to a couple of feet, so I would have to agree that the GPS system on the iPhone is weak, but then again with all that technology crammed into such a small device it does a pretty good job (when it works!) Beware of golf apps in the Apps Store that can provide accurate distances to the green, as it can be misleading. 30 feet is 2 club lengths for most people!

[QUOTE]In your case, make sure it's got a clear view from above you, down towards the South. (There are no GPS satellites orbiting north of the North Sea.)[/QUOTE]

I believe you may want to check your info -- the GPS satellite constellation is a low-Earth orbit matrix, not an Equator (have to face south) geosynchronous orbit constellation (~23,000 miles out). The GPS sat orbits look very much like a net which encloses the entire planet. Because they are in low Earth orbit, they are in constant motion relative to the surface of the Earth, with some in near polar orbits -- so there's lots of times when there are birds at higher latitudes than the North Sea.

So there's no need to face in any particular direction; as long as your device has a clear view of the sky, it can try to pick up any GPS sat signal which is above the horizon in any direction. Of course, the sats down by the horizon will have weaker signals until they are move overhead, but it doesn't matter which direction around the device they are.

The GPS orbits only look like a net in poorly drawn graphics. They are neither arranged in a sphere, nor do they ever come even close to crossing the poles.

The GPS satellites are divided into six medium earth orbital planes at 60 degree intervals around the equator. They orbit in their plane around the earth twice a day.

Each of the six orbital planes are set at an inclination of 55 degrees. That means they never orbit directly above anything past +/-55 degress latitude. Visualize Saturn's rings tilted at about half way to vertical and you'll get the right idea.

One of the side effects of the 55 degrees, is that it's difficult (or impossible) to get overhead coverage in high latitude cities which have tall buildings. To get around this for their own country's needs, the Russian satellites orbit at a greater inclination of ~65 degrees.

As you go even further towards the poles, you'll see some satellites from the other side of the earth, but most will be pretty low on the horizon. Usable but not nearly as good as the view is from lower latitudes. This is by design.

Well, in MobilDev's defense, if the chipset can use the WAAS, EGNOS and MSAS satellites then a good view to the equator is also useful.

Most modern chipsets can use these birds if they can see them, which is not that easy from northern locations. (For some values of "Northern").

These are located on geostationary satellites.

The geostationary satellites do provide a signals very similar to that of the GPS-satellites and on the same frequency. Therefor these satellites may be used for position calculation and additionally, the correction data sent out can be used to improve accuracy for position calculation with all GPS satellites.

Here, this graphic of a sample GPS satellite ground track (in red) should help. Notice that because of the 55 degree inclination, their overhead ground tracks never go past that amount in north or south latitude. [More info on orbits|http://www.kowoma.de/en/gps/orbits.htm].

!http://www.kowoma.de/en/gps/groundtrack_prn18.gif!

The shaded blue area is the coverage area when the satellite is at the yellow dot. You can easily grasp that if you're in the North Sea, you'll always have to look anywhere from directly above you, to down towards the equator, to listen to any particular satellite.

Now that we've established the phone does indeed have GPS receiver, take a look at this: http://www.inavx.net/

Carrying the maps 'preloaded' would eliminate the need for a network connection.

The most pressing question is why are you using a non-intrinsically safe mobile phone outside of the accomodation of an offshore installation.