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Diffstat (limited to 'src/modules/systemlib/airspeed.c')
| -rw-r--r-- | src/modules/systemlib/airspeed.c | 111 |
1 files changed, 111 insertions, 0 deletions
diff --git a/src/modules/systemlib/airspeed.c b/src/modules/systemlib/airspeed.c new file mode 100644 index 000000000..15bb833a9 --- /dev/null +++ b/src/modules/systemlib/airspeed.c @@ -0,0 +1,111 @@ +/**************************************************************************** + * + * Copyright (C) 2012-2013 PX4 Development Team. All rights reserved. + * Author: Lorenz Meier <lm@inf.ethz.ch> + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions + * are met: + * + * 1. Redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer. + * 2. Redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in + * the documentation and/or other materials provided with the + * distribution. + * 3. Neither the name PX4 nor the names of its contributors may be + * used to endorse or promote products derived from this software + * without specific prior written permission. + * + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS + * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT + * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS + * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE + * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, + * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, + * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS + * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED + * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT + * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN + * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE + * POSSIBILITY OF SUCH DAMAGE. + * + ****************************************************************************/ + +/** + * @file airspeed.c + * Airspeed estimation + * + * @author Lorenz Meier <lm@inf.ethz.ch> + * + */ + +#include <stdio.h> +#include <math.h> +#include "conversions.h" +#include "airspeed.h" + + +/** + * Calculate indicated airspeed. + * + * Note that the indicated airspeed is not the true airspeed because it + * lacks the air density compensation. Use the calc_true_airspeed functions to get + * the true airspeed. + * + * @param differential_pressure total_ pressure - static pressure + * @return indicated airspeed in m/s + */ +float calc_indicated_airspeed(float differential_pressure) +{ + + if (differential_pressure > 0) { + return sqrtf((2.0f*differential_pressure) / CONSTANTS_AIR_DENSITY_SEA_LEVEL_15C); + } else { + return -sqrtf((2.0f*fabs(differential_pressure)) / CONSTANTS_AIR_DENSITY_SEA_LEVEL_15C); + } + +} + +/** + * Calculate true airspeed from indicated airspeed. + * + * Note that the true airspeed is NOT the groundspeed, because of the effects of wind + * + * @param speed_indicated current indicated airspeed + * @param pressure_ambient pressure at the side of the tube/airplane + * @param temperature_celsius air temperature in degrees celcius + * @return true airspeed in m/s + */ +float calc_true_airspeed_from_indicated(float speed_indicated, float pressure_ambient, float temperature_celsius) +{ + return speed_indicated * sqrtf(CONSTANTS_AIR_DENSITY_SEA_LEVEL_15C / get_air_density(pressure_ambient, temperature_celsius)); +} + +/** + * Directly calculate true airspeed + * + * Note that the true airspeed is NOT the groundspeed, because of the effects of wind + * + * @param total_pressure pressure inside the pitot/prandtl tube + * @param static_pressure pressure at the side of the tube/airplane + * @param temperature_celsius air temperature in degrees celcius + * @return true airspeed in m/s + */ +float calc_true_airspeed(float total_pressure, float static_pressure, float temperature_celsius) +{ + float density = get_air_density(static_pressure, temperature_celsius); + if (density < 0.0001f || !isfinite(density)) { + density = CONSTANTS_AIR_DENSITY_SEA_LEVEL_15C; +// printf("[airspeed] Invalid air density, using density at sea level\n"); + } + + float pressure_difference = total_pressure - static_pressure; + + if(pressure_difference > 0) { + return sqrtf((2.0f*(pressure_difference)) / density); + } else + { + return -sqrtf((2.0f*fabs(pressure_difference)) / density); + } +} |