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AP_Baro: extend the atmospheric model to higher altitudes

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This commit is contained in:
Andrew Tridgell 2013-07-20 23:00:41 +10:00
parent 5a68c515dc
commit ebebee4f06
1 changed files with 36 additions and 8 deletions
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44
libraries/AP_Baro/AP_Baro_HIL.cpp
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@ -31,18 +31,46 @@ uint8_t AP_Baro_HIL::read()
return result;
}
// ==========================================================================
// based on tables.cpp from http://www.pdas.com/atmosdownload.html
/*
Compute the temperature, density, and pressure in the standard atmosphere
Correct to 20 km. Only approximate thereafter.
*/
static void SimpleAtmosphere(
const float alt, // geometric altitude, km.
float& sigma, // density/sea-level standard density
float& delta, // pressure/sea-level standard pressure
float& theta) // temperature/sea-level standard temperature
{
const float REARTH = 6369.0f; // radius of the Earth (km)
const float GMR = 34.163195f; // gas constant
float h=alt*REARTH/(alt+REARTH); // geometric to geopotential altitude
if (h<11.0)
{ // Troposphere
theta=(288.15f-6.5f*h)/288.15f;
delta=powf(theta, GMR/6.5f);
}
else
{ // Stratosphere
theta=216.65f/288.15f;
delta=0.2233611f*expf(-GMR*(h-11.0f)/216.65f);
}
sigma=delta/theta;
}
void AP_Baro_HIL::setHIL(float altitude_msl)
{
// approximate a barometer
// see http://en.wikipedia.org/wiki/Atmospheric_pressure
float sigma, delta, theta;
const float p0 = 101325;
const float L = 0.0065;
const float T0 = 288.15;
const float M = 0.0289644;
const float R = 8.31447;
float p = p0 * pow(1.0 - (L*altitude_msl)/T0, (GRAVITY_MSS*M)/(R*L));
float T = 31.2 - altitude_msl * L;
SimpleAtmosphere(altitude_msl*0.001, sigma, delta, theta);
float p = p0 * delta;
float T = 30 * theta;
_count++;
_pressure_sum += p;