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AP_Baro: more precise altitude calculation on PX4

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if not using an AVR CPU then use a more computationally expensive
altitude calculation, which is more precise at higher altitudes
This commit is contained in:
Paul Riseborough 2013-06-26 18:30:33 +10:00 committed by Andrew Tridgell
parent 459c47fa46
commit 3b98bbd159
1 changed files with 12 additions and 3 deletions
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15
libraries/AP_Baro/AP_Baro.cpp
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@ -106,12 +106,21 @@ float AP_Baro::get_altitude(void)
return _altitude;
}
// this has no filtering of the pressure values, use a separate
// filter if you want a smoothed value. The AHRS driver wants
// unsmoothed values
#if defined(__AVR_ATmega1280__) || defined(__AVR_ATmega2560__)
// on AVR use a less exact, but faster, calculation
scaling = (float)_ground_pressure / (float)get_pressure();
temp = ((float)_ground_temperature) + 273.15f;
_altitude = logf(scaling) * temp * 29.271267f;
#else
// on faster CPUs use a more exact calculation
scaling = (float)get_pressure() / (float)_ground_pressure;
temp = ((float)_ground_temperature) + 273.15f;
// This is an exact calculation that is within +-2.5m of the standard atmosphere tables
// in the troposphere (up to 11,000 m amsl).
_altitude = 153.8462f * temp * (1.0f - expf(0.190259f * logf(scaling)));
#endif
_last_altitude_t = _last_update;