|
|
| Re: Canarsie CBTC (100330) | |||
 |
|||
| Home > SubChat | |||
|
[ Read Responses | Post a New Response | Return to the Index ] |
|
||
|
Re: Canarsie CBTC |
|
|
Posted by AlM on Sat Jun 18 11:03:51 2005, in response to Re: Canarsie CBTC, posted by RonInBayside on Sat Jun 18 10:44:55 2005. This error then grows with succeeding time points.Um, no. The error in position as measured by GPS never exceeds 15 feet from your true psoition. Therefore, the more time between measurements, the less the error in velocity. If I measure my position at t=0 and t=15, the error of each positional estimate is still only 15 feet. Subtracting, my maximum possible mistake is 30 feet, or 2 feet per second. Now if I measure position at t=0 and t=30, my maximum possible positional error in the difference of the measurements is still only 30 feet, so my maximum error in the velocity calculation is 1 foot per second. And as I mentioned elsewhere I think the error in velocity is much less because successive position erros are strongly correlated. There is one other issue, however. What if you don't get a signal? The satellite signals are so weak that some unauthorized nearby interference could kill some of them temporarily. As I mentioned, this happens frequently in Manhattan with a hand held GPS. |
|
|
|