No Way That Disney is Using GPS for a Ride System

Okay you guys, I've been reading all the hype and hoopla about the new rides at DLP.  All of them seem pretty cool and pretty reasonable until you start reading about how the ride system for the new proposed Ratatouille ride will supposedly use GPS like a ride in Tokyo (Pooh's Hunny Hunt).

First let me say, as an Engineer and as a guy who works for the US Government, there is no way a ride system like this uses GPS.  Right off the bat, it just doesn't pass the smell test. 

First, if a ride system used it, it would presume GPS is incredibly accurate, which by itself IT'S NOT (for lots of complicated reasons related to not only receiver error, but also the way the satellite system is designed).  Secondly, the ride is in a building and any of you who own a portable GPS will know that it doesn't work inside without a lot of work.  Thirdly, most GPS receivers under $1,000 have typical error rates of something like not greater than 15 meters 95% of the time.  That means 5% of the time, you could be anywhere in the world and still meet the accuracy requirement.

You can get fairly accurate with Differential GPS, but even that requires an alternate radio with a position established by other means (usually surveying) that feeds a radio signal to a receiver to augment the satellite.  But even with a good receiver, this is still usually only 1 meter or so accuracy ON AVERAGE.  That means the ride system would have plus or minus 6.5 FEET of slack, which is just bad!

Lastly, you could also check Wikipedia, older Laughing Place articles, etc. to find out that it uses a highly customized, and very secret local positioning system. 

My guess would be that it uses a combination of radio triangulation, markers on the floor/walls, and maybe even a laser range finder type system, which are very accurate.  However, given that one Laughing Place article noted that cell phones interfered with the system, and therefore were banned from the ride, my bet (if that is true) would  be based on a variety of radio based transmitters using a local datum doing something LIKE GPS using differential time signals to establish the cars location. 

If you own an iPhone or a phone were Google Maps uses the radio transmitter to show you location use something very similar using cell phone towers.  It takes at least 2, and preferably 3, to get a decent CEP (circular error of probability, which means how big a circle has to be to make sure you are INSIDE it). 

If you have a highly accurate clock (which you CAN use GPS for BTW) and one highly precise physical location to use as a datum, with enough antennas in the building and a fast enough computer on the vehicle, you can find yourself with pretty darn good accuracy.

But it is NOT GPS.  

If you want to see some fantastic survey pictures of DisneyWorld, go check out this web site!