From fab110d21f147e5064ff140aadac649017fa466e Mon Sep 17 00:00:00 2001
From: Lorenz Meier <lm@inf.ethz.ch>
Date: Wed, 21 Aug 2013 18:13:01 +0200
Subject: Moved math library to library dir, improved sensor-level HIL, cleaned
 up geo / conversion libs

---
 src/lib/mathlib/math/filter/LowPassFilter2p.cpp | 77 +++++++++++++++++++++++++
 1 file changed, 77 insertions(+)
 create mode 100644 src/lib/mathlib/math/filter/LowPassFilter2p.cpp

(limited to 'src/lib/mathlib/math/filter/LowPassFilter2p.cpp')

diff --git a/src/lib/mathlib/math/filter/LowPassFilter2p.cpp b/src/lib/mathlib/math/filter/LowPassFilter2p.cpp
new file mode 100644
index 000000000..efb17225d
--- /dev/null
+++ b/src/lib/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
+
-- 
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