forked from Archive/PX4-Autopilot
112 lines
4.0 KiB
C
112 lines
4.0 KiB
C
/****************************************************************************
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*
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* Copyright (C) 2012-2013 PX4 Development Team. All rights reserved.
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* Author: Lorenz Meier <lm@inf.ethz.ch>
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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* 3. Neither the name PX4 nor the names of its contributors may be
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* used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*
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****************************************************************************/
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/**
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* @file airspeed.c
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* Airspeed estimation
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*
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* @author Lorenz Meier <lm@inf.ethz.ch>
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*
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*/
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#include <stdio.h>
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#include <math.h>
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#include "conversions.h"
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#include "airspeed.h"
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/**
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* Calculate indicated airspeed.
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*
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* Note that the indicated airspeed is not the true airspeed because it
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* lacks the air density compensation. Use the calc_true_airspeed functions to get
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* the true airspeed.
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*
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* @param differential_pressure total_ pressure - static pressure
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* @return indicated airspeed in m/s
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*/
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float calc_indicated_airspeed(float differential_pressure)
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{
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if (differential_pressure > 0) {
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return sqrtf((2.0f*differential_pressure) / CONSTANTS_AIR_DENSITY_SEA_LEVEL_15C);
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} else {
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return -sqrtf((2.0f*fabs(differential_pressure)) / CONSTANTS_AIR_DENSITY_SEA_LEVEL_15C);
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}
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}
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/**
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* Calculate true airspeed from indicated airspeed.
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*
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* Note that the true airspeed is NOT the groundspeed, because of the effects of wind
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*
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* @param speed_indicated current indicated airspeed
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* @param pressure_ambient pressure at the side of the tube/airplane
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* @param temperature_celsius air temperature in degrees celcius
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* @return true airspeed in m/s
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*/
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float calc_true_airspeed_from_indicated(float speed_indicated, float pressure_ambient, float temperature_celsius)
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{
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return speed_indicated * sqrtf(CONSTANTS_AIR_DENSITY_SEA_LEVEL_15C / get_air_density(pressure_ambient, temperature_celsius));
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}
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/**
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* Directly calculate true airspeed
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*
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* Note that the true airspeed is NOT the groundspeed, because of the effects of wind
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*
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* @param total_pressure pressure inside the pitot/prandtl tube
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* @param static_pressure pressure at the side of the tube/airplane
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* @param temperature_celsius air temperature in degrees celcius
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* @return true airspeed in m/s
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*/
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float calc_true_airspeed(float total_pressure, float static_pressure, float temperature_celsius)
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{
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float density = get_air_density(static_pressure, temperature_celsius);
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if (density < 0.0001f || !isfinite(density)) {
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density = CONSTANTS_AIR_DENSITY_SEA_LEVEL_15C;
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printf("[airspeed] Invalid air density, using density at sea level\n");
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}
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float pressure_difference = total_pressure - static_pressure;
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if(pressure_difference > 0) {
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return sqrtf((2.0f*(pressure_difference)) / density);
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} else
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{
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return -sqrtf((2.0f*fabs(pressure_difference)) / density);
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}
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}
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