mathlib: added LowPassFilter2p object

used in gyro and accel drivers for better filtering

src/modules/mathlib/math/filter/LowPassFilter2p.cpp

@@ -0,0 +1,77 @@
+// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
+
+/****************************************************************************
+ *
+ *   Copyright (C) 2012 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	LowPassFilter.cpp
+/// @brief	A class to implement a second order low pass filter 
+/// Author: Leonard Hall <LeonardTHall@gmail.com>
+
+#include "LowPassFilter2p.hpp"
+#include "math.h"
+
+namespace math
+{
+
+void LowPassFilter2p::set_cutoff_frequency(float sample_freq, float cutoff_freq)
+{
+    _cutoff_freq = cutoff_freq;
+    float fr = sample_freq/_cutoff_freq;
+    float ohm = tanf(M_PI_F/fr);
+    float c = 1.0f+2.0f*cosf(M_PI_F/4.0f)*ohm + ohm*ohm;
+    _b0 = ohm*ohm/c;
+    _b1 = 2.0f*_b0;
+    _b2 = _b0;
+    _a1 = 2.0f*(ohm*ohm-1.0f)/c;
+    _a2 = (1.0f-2.0f*cosf(M_PI_F/4.0f)*ohm+ohm*ohm)/c;
+}
+
+float LowPassFilter2p::apply(float sample)
+{
+    // do the filtering
+    float delay_element_0 = sample - _delay_element_1 * _a1 - _delay_element_2 * _a2;
+    if (isnan(delay_element_0) || isinf(delay_element_0)) {
+        // don't allow bad values to propogate via the filter
+        delay_element_0 = sample;
+    }
+    float output = delay_element_0 * _b0 + _delay_element_1 * _b1 + _delay_element_2 * _b2;
+    
+    _delay_element_2 = _delay_element_1;
+    _delay_element_1 = delay_element_0;
+
+    // return the value.  Should be no need to check limits
+    return output;
+}
+
+} // namespace math
+

src/modules/mathlib/math/filter/LowPassFilter2p.hpp

@@ -0,0 +1,78 @@
+// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
+
+/****************************************************************************
+ *
+ *   Copyright (C) 2012 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	LowPassFilter.h
+/// @brief	A class to implement a second order low pass filter 
+/// Author: Leonard Hall <LeonardTHall@gmail.com>
+/// Adapted for PX4 by Andrew Tridgell
+
+#pragma once
+
+namespace math
+{
+class __EXPORT LowPassFilter2p
+{
+public:
+    // constructor
+    LowPassFilter2p(float sample_freq, float cutoff_freq) {
+        // set initial parameters
+        set_cutoff_frequency(sample_freq, cutoff_freq);
+        _delay_element_1 = _delay_element_2 = 0;
+    }
+
+    // change parameters
+    void set_cutoff_frequency(float sample_freq, float cutoff_freq);
+
+    // apply - Add a new raw value to the filter 
+    // and retrieve the filtered result
+    float apply(float sample);
+
+    // return the cutoff frequency
+    float get_cutoff_freq(void) const {
+        return _cutoff_freq;
+    }
+
+private:
+    float           _cutoff_freq; 
+    float           _a1;
+    float           _a2;
+    float           _b0;
+    float           _b1;
+    float           _b2;
+    float           _delay_element_1;        // buffered sample -1
+    float           _delay_element_2;        // buffered sample -2
+};
+
+} // namespace math

src/modules/mathlib/math/filter/module.mk

@@ -0,0 +1,44 @@
+############################################################################
+#
+#   Copyright (c) 2012, 2013 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.
+#
+############################################################################
+
+#
+# filter library
+#
+SRCS		 = LowPassFilter2p.cpp
+
+#
+# In order to include .config we first have to save off the
+# current makefile name, since app.mk needs it.
+#
+APP_MAKEFILE	:= $(lastword $(MAKEFILE_LIST))
+-include $(TOPDIR)/.config