globalloon wrote:
that’s a nice bit of kit
I covered the mile home from work in 3 minutes before :surprised (is mostly downhill, but the route was cross-town!
technical explanation, GL?
when you first switch on on a GPS receiver it needs to “acquire” the initial position.
to do this the equipment has to pick up signals from up to 12 satellites, work out the signal strength from each one, decode some random bit pattern and the current time, deal with Uncle Sam’s encryption algorithm, and from this huge matrix of constantly changing numbers calculate the current position in latitude and longitude.
Because of the way I always set up GPS receivers used in Britain the software then has to convert it into the ordnance survey grid reference for your location.
That is a lot of very complicated maths, even for a computer.
If you are also moving at the same time this process is happening, there is a chance that an overflow error can occur in the software and/or radio interference can garble the data – and the results of the calculations are bogus.
the logs for when this error happened actually show me proceeding at 80-100mph, 92 feet above sea level in the North Atlantic Ocean between Exmouth and Weymouth. At the time, I was going towards the North of Ipswich, at the side of the Orwell flood barrier. The receiver eventually sorted itself out after 30 seconds and was reporting rather more sensible locations..
This is a good example of why GPS is not a substitute for local knowledge and/or conventional maps/navigation skills, its only an aid to navigation…
My real top speed is about 20-25 mph on the flats. I have reached 40mph downhill around the Wantage area of West Berkshire before on my touring bike, so USEs top speed is perfectly possible.
Bike computers need to be set up correctly for the tyre size, but I’ve checked mine against the GPS (which is accurate when correctly locked on to the satellites!) and they are within 5% of each others readings.
