RNS:: Speedometer GPS forum thread

	Speedo GPS Accuracy/Resolutuon
	ffastffrank wrote: March 18th, 2009 I am interested in measuring with accuracy the speed and path of a model sailboat which is only 1 foot long and called a "Footy". Max speed is ~ 2 MPH. What resolution & accuracy should I expect? You say it is accurate, but there are no specs stated. ffastffrank wrote: March 18th, 2009 By the way, my AMYA membership number (www.modelyacht.org or www.tanglewoodmyc.com) is 14,802 and this is USA only. If there is good resolution (even 0.1 mph) and it would work with a small unit like a "Freedom Keychain" sensor, this could generate a lot of interest in the model sailboat racing world. Set me up w/a system & I will run tests and report on other world wide forums such as www.rcsailing.net Radoslaw Nowak (RNS::) wrote: March 19th, 2009 In short: I'm afraid that the GPS technology is not appropriate for this use. Most GPS receivers do not precisely measure speeds lower than 2 MPH. The high accuracy that is mentioned in our product's description is achieved over 5 MPH and increases with speed. I mean that while tracking at least 4 satellites (which is nothing unusual for GPS receivers) the accuracy of GPS speedometer reaches the accuracy of a typical car speedometer at 5 MPH. Dan wrote: March 27th, 2009 Is velocity calculated in 3 dimensions? Would it correctly show velocity when skydiving or downhill skiing? Frank Thorley wrote: March 27th, 2009 If not GPS, what about some other solutions??? Radoslaw Nowak (RNS::) wrote: March 28th, 2009 No, Dan, the velocity is calculated over the ground only. This is mostly because popular GPS receivers aren't very accurate as far as altitude is concerned. This cannot be fixed by any software. As a result, if you're skydiving directly downwards, then your GPS speed would be zero. You can use PathAway, an application that shows vertical speed - but as I said - it cannot be very accurate.

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