Hello everybody, check out this nice article about the limitations of GPS-Altitude and Barometric Altitude
http://docs.controlvision.com/pages/gps_altimetry.php Somewhere I read that the vertical GPS-error is about 1,5 to 3 times greater than the lateral error. Please correct me if thats wrong. According to this Article http://de.wikipedia.org/wiki/Global_Positioning_System#Genauigkeit_der_Positionsbestimmung the lateral error is at the moment within 7,8 m in 95% of the measurements. Which would make the vertical error maximum 24m. Good enough for my final glide, I think. Personally, as for the accuracy of the GPS Altitude, I have only made very good experience. With the error seldom more than 10m. However for airpace limits corrected baro altitude is relevant. Please also note that the raw pressure readouts that for example Volkslogger gives you are not yet corrected. It is the pressure altitude above a hardware specific pressure level. (Not sure if it's calibrated to 1013, but I will ask the Garrechts about this) When the glider is on the ground at known airfield elevation, the NMEA-Pressure-readout can be calibrated to correct pressure altitude (QHN-correction) This is the same as if you set your altimeter to airfield elevation before takeoff. If the actual QNH is known, as it is during competions (on your task sheet), it is also possible to calibrate your NMEA-Pressure-Source (e.g. Volkslogger) to 1013 hPa pressure level. This gives you correct readouts for FL-Airspaces. With the set QNH the correct pressure altitude (for ASL-Airspaces) is easily calculated from the altitude above 1013, and the advantage is that you can correct the QNH in flight and that will affect Pressure Altitude (QNH) but not Pressure Altitude (1013) If that didn't confuse you, you might want to read and comment on the Trac ticket I created on this issue. It's my idea on how xcsoar could handle the different altitudes... http://www.xcsoar.org/trac/ticket/442 Greets Henrik Am 06.10.2010 01:48, schrieb karaka29211: > Be aware of the difference between the terms "flight level" which is > referenced to the standard pressure of 1013.2 mb and "altitude" referenced > to local area pressure. Depending on whether the flight is conducted above > or below the transition layer, the ATC airspace violations are judged with > different base pressure criteria. Whether they are judged by the > competition director to have occured is a matter for the local competition > rules. > > ian-187 wrote: >> On 05/10/2010 00:02, Ian wrote: >> >> >> >> During that flight I got ATC clearance to enter the local TMA. So with >> valid airspace data I get lots of warnings on the replay. However they >> would be more accurate using the B500's "rounded off to flight level" >> barometric hight than GPS hights. Can we relook at this one? >> >> Thanks >> >> Ian >> >> ------------------------------------------------------------------------------ >> Beautiful is writing same markup. Internet Explorer 9 supports >> standards for HTML5, CSS3, SVG 1.1, ECMAScript5, and DOM L2& L3. >> Spend less time writing and rewriting code and more time creating great >> experiences on the web. Be a part of the beta today. >> http://p.sf.net/sfu/beautyoftheweb >> _______________________________________________ >> Xcsoar-user mailing list >> Xcsoar-user@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/xcsoar-user >> >> ------------------------------------------------------------------------------ Beautiful is writing same markup. Internet Explorer 9 supports standards for HTML5, CSS3, SVG 1.1, ECMAScript5, and DOM L2 & L3. Spend less time writing and rewriting code and more time creating great experiences on the web. Be a part of the beta today. http://p.sf.net/sfu/beautyoftheweb _______________________________________________ Xcsoar-user mailing list Xcsoar-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/xcsoar-user
