added a weathervane library

- computes a yaw-rate setpoint that tries to rotate the nose of the vehicle
into the relative wind.

Signed-off-by: Roman <bapstroman@gmail.com>

src/lib/WeatherVane/WeatherVane.hpp

@@ -0,0 +1,80 @@
+/****************************************************************************
+ *
+ *   Copyright (c) 2018 PX4 Development Team. All rights reserved.
+ *
+ * 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 WeatherVane.hpp
+ * @author Ivo Drescher
+ * @author Roman Bapst <roman@auterion.com>
+ *
+ * Weathervane controller.
+ *
+ */
+
+#pragma once
+
+#include <matrix/matrix/math.hpp>
+
+class WeatherVane
+{
+public:
+	WeatherVane();
+
+	~WeatherVane() {};
+
+	void activate() {_is_active = true;}
+
+	void deactivate() {_is_active = false;}
+
+	bool is_active() {return _is_active;}
+
+	void update(matrix::Quatf q_sp_prev, float yaw);
+
+	float get_weathervane_yawrate();
+
+	void set_weathervane_gain(float gain) {_wv_gain = gain;}
+
+	void set_min_roll_rad(float min_roll_rad) {_wv_min_roll_rad = min_roll_rad;}
+
+	void set_yawrate_max_rad(float yawrate_max_rad) {_wv_yawrate_max_rad = yawrate_max_rad;}
+
+private:
+	matrix::Quatf _q_sp_prev;	// previous attitude setpoint quaternion
+	float _yaw = 0.0f;					// current yaw angle
+
+	bool _is_active = true;
+
+	float _wv_gain = 1.0f;		// gain that maps excessive roll angle setpoint to yawrate setoint [1/s]
+	float _wv_min_roll_rad = 0.01f;		// minimum roll angle setpoint for the controller to output a non-zero yawrate setpoint
+	float _wv_yawrate_max_rad = 1.0f;	// maximum yaw-rate the controller will output
+
+};