From 13fc6703862862f4263d8d5d085b7a16b87190e1 Mon Sep 17 00:00:00 2001
From: Lorenz Meier <lm@inf.ethz.ch>
Date: Sun, 28 Apr 2013 09:54:11 +0200
Subject: Moved last libs, drivers and headers, cleaned up IO build

---
 src/modules/systemlib/airspeed.c | 111 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 111 insertions(+)
 create mode 100644 src/modules/systemlib/airspeed.c

(limited to 'src/modules/systemlib/airspeed.c')

diff --git a/src/modules/systemlib/airspeed.c b/src/modules/systemlib/airspeed.c
new file mode 100644
index 000000000..264287b10
--- /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);
+	}
+}
-- 
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