On 05/10/2010 10:21, Tobias Bieniek wrote: > Why do you think that the _rounded_ baro altitude would be more > accurate then the GPS height?!
I have sent Tobias a detailed reply with more graphs, but that message is too big for this list. I have edited this replay and attached a graph of GPS altitude verses barometric altitude for the flight. The data came from my volkslogger and the graphs were drawn with a nice utility "GPLIGC". The difference between the two altitudes average between 200 and 400 feet for the flight, The error with the rounded baro altitude from the B500 would be between 0 and 100'. More than this, the rounding is always upwards, which for gliders is usually the "safe" error for airspace considerations. There was a period in this flight when I got to within 100' of controlled airspace (barometric altitude with std QNH). The GPS altitude at this point shows a 200' airspace incursion. Actually I got closer to the airspace than I should have, but I was distracted playing with the PDA ... (Later I got ATC clearance and went higher). So technically the B500's rounded barometric altitude is usefully more accurate than GPS altitude. But having said that, I don't think this is a high priority, just a "nice to have". There are probably not many of us B500 users using Xcsoar. Airspace warning from GPS alitude would still be just about as useful. Thanks for all your efforts! Ian
<<attachment: baro_vs_gps_small.png>>
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