4 ms·
From memory the opening of a military technology to the general public forbid using it to this level of accuracy? Maybe it was only sub metre accuracy?
by taitems 5y ago
From memory the opening of a military technology to the general public forbid using it to this level of accuracy? Maybe it was only sub metre accuracy?
- Retric 5y agoThat was removed a long time ago. During the 1990s, GPS quality was degraded by the United States government in a program called "Selective Availability"; this was discontinued on May 1, 2000 by a law signed by President Bill Clinton. GPS can get extreme precision as in mm when given a long tine and a fixed location, which is mostly useful for geologists. However, you can get close to that using extreme precision accelerometers and GPS, but it’s rarely worth the cost.
- dhsysusbsjsi 5y agoA rough guide: The GPS signal works on two codes: coarse acquisition (C/A) and precision (P) codes. The P codes are 1 week long and require a secret key even to this day. C/A is I think a few hundred milliseconds and easily locked onto. They used to use C/A for what it says: coarse acquisition of where you are (space and time), to work out where you are in the P code signal to start looking. Apparently a difficult problem without the C/A to start you in the right place. To stop baddies using GPS for anything evil, the C/A had an error built in. This error in C/A is what Bill Clinton removed. To this day military still can use P codes and it is still possible for the C/A to go out to lunch. But practically this is unlikely to happen given the amount of civil applications dependent on accurate gps.
- taitems 5y agoFascinating replies from both of you, thanks.