Someone has posted that GPS do not work at Sahara, I will argue that it won't work at places with low coverage from GPS Mountain based antennas.
What happen is that antennas all over the world cover with frequencies a lot of space and then you have your signal to GPS.
The best place to put such an antenna is at mountains, there you can has a lot of connections all over the world, second thing is what we call microwave:
You launch signals from far away and the signal get caught on ground and allow you navigate safely.
Rayzor once said there is a specific frequency - yes this is the frequency for GPS Mountain based antennas.
When we know that antennas are hundreds of kilometers far away even thousands of kilometers we can assume that the antenna is in a very remote part of the world, or at very far away part of the world,
The world is full of signals of antennas that's all.
There are satellites at space they produce useless photos but not GPS signal.
Disclaimer:
That's my theory I am not a professional I am just want to speculate according to the laws of this forum.
How many mountains.are there in the middle of the oceans ?
There are many ways to spread signals across the ocean.
Okay. Like, which?
1) Nearby mountain antennas can launch very powerful rays to the ocean and then you can pick them from high altitude,
2)you can use the stratosphere or the concavity of the earth.
3)powerful antennas can launch very powerful rays and signal to the sky then the rays declining or sinking down and what you have to do is to pick the signal from air.
But you kind of miss some key points.
1. Based on GPS data, you can calculate the exact position of any given GPS satellite that your GPS chip is receiving from
2. "Very powerful rays" is.. Well, vague. What kind of "rays"? Frequency, band etc. Those kind of information are kind of... Important. Different bands and frequencies have different properties, pros and cons, especially when it comes to either bouncing off of he upper atmosphere or following the earth's curvature (like VHF for instance)
3. Picking something from high altitudes, I assume that you them refer to line-of-sight. With what then? Extremely tall GPS antennas?
1)maybe you can calculate the antenna distance from you and it could be very far away antenna as well.
Ok. You didn't answer my two other points. Please make an effort to.
And no. GPS data doesn't simply consist of a frequency data and a simple direction. I can tell you with 100% certainty, that the data I read from a GPS chip doesn't come from an antenna. Besides the actual coordinates you'd expect from positioning, you also get stuff like azimuth, angle, altitude (in centimeters for consumer grade chips), latitude, longitude, speed, day, month, year, time stamps, and heaps of other data specific to your configuration.
Please find a better explanation, and while you do, please know that I work with this every single day.