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| Re: Canarsie CBTC (100298) | |||
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Re: Canarsie CBTC |
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Posted by RonInBayside on Sat Jun 18 09:30:18 2005, in response to Re: Canarsie CBTC, posted by Stephen Bauman on Sat Jun 18 09:17:35 2005. The error bar here is 30 feet (+ or - 15 feet). So if GPS is used entirely unassisted, you could be off, in the worst worst case by the length of a commuter rail car within six seconds; it is likely your error will be less than that.But you can "zero" your error with the use of a double-check (such as a fixed beacon). Recall that pilots can correct the error o an inertial navigation system by double-checking using a magnetic compass (set aside GPS and other aids for a moment in that industry). If you use fixed beacons, using GPS could allow you to use fewer beacons because you would use beacons at intervals to correct the error of your GPS. You would then define how long an interval you could tolerate (how bad the error gets before you have to correct it). That interval could vary depending on where you are. Would your tolerance for position error on GPS not be greater in a marshaling yard, train station or busy interlocking (like Harold) than out on a stretch of track where trains pass once per hour? |
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