Diff: LowpassFilter.cpp

Revision:

0:bb408887ab78

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/LowpassFilter.cpp	Fri Mar 09 15:29:36 2018 +0000
@@ -0,0 +1,112 @@
+/*
+ * LowpassFilter.cpp
+ * Copyright (c) 2018, ZHAW
+ * All rights reserved.
+ */
+
+#include <cmath>
+#include "LowpassFilter.h"
+
+using namespace std;
+
+/**
+ * Creates a LowpassFilter object with a default cutoff frequency of 1000 [rad/s].
+ */
+LowpassFilter::LowpassFilter() {
+    
+    period = 1.0f;
+    frequency = 1000.0f;
+    
+    a11 = (1.0f+frequency*period)*exp(-frequency*period);
+    a12 = period*exp(-frequency*period);
+    a21 = -frequency*frequency*period*exp(-frequency*period);
+    a22 = (1.0f-frequency*period)*exp(-frequency*period);
+    b1 = (1.0f-(1.0f+frequency*period)*exp(-frequency*period))/frequency/frequency;
+    b2 = period*exp(-frequency*period);
+    
+    x1 = 0.0f;
+    x2 = 0.0f;
+}
+
+/**
+ * Deletes the LowpassFilter object.
+ */
+LowpassFilter::~LowpassFilter() {}
+
+/**
+ * Resets the filtered value to zero.
+ */
+void LowpassFilter::reset() {
+    
+    x1 = 0.0f;
+    x2 = 0.0f;
+}
+
+/**
+ * Resets the filtered value to a given value.
+ * @param value the value to reset the filter to.
+ */
+void LowpassFilter::reset(float value) {
+    
+    x1 = value/frequency/frequency;
+    x2 = (x1-a11*x1-b1*value)/a12;
+}
+
+/**
+ * Sets the sampling period of the filter.
+ * This is typically the sampling period of the periodic task of a controller that uses this filter.
+ * @param the sampling period, given in [s].
+ */
+void LowpassFilter::setPeriod(float period) {
+    
+    this->period = period;
+    
+    a11 = (1.0f+frequency*period)*exp(-frequency*period);
+    a12 = period*exp(-frequency*period);
+    a21 = -frequency*frequency*period*exp(-frequency*period);
+    a22 = (1.0f-frequency*period)*exp(-frequency*period);
+    b1 = (1.0f-(1.0f+frequency*period)*exp(-frequency*period))/frequency/frequency;
+    b2 = period*exp(-frequency*period);
+}
+
+/**
+ * Sets the cutoff frequency of this filter.
+ * @param frequency the cutoff frequency of the filter in [rad/s].
+ */
+void LowpassFilter::setFrequency(float frequency) {
+    
+    this->frequency = frequency;
+    
+    a11 = (1.0f+frequency*period)*exp(-frequency*period);
+    a12 = period*exp(-frequency*period);
+    a21 = -frequency*frequency*period*exp(-frequency*period);
+    a22 = (1.0f-frequency*period)*exp(-frequency*period);
+    b1 = (1.0f-(1.0f+frequency*period)*exp(-frequency*period))/frequency/frequency;
+    b2 = period*exp(-frequency*period);
+}
+
+/**
+ * Gets the current cutoff frequency of this filter.
+ * @return the current cutoff frequency in [rad/s].
+ */
+float LowpassFilter::getFrequency() {
+    
+    return frequency;
+}
+
+/**
+ * Filters a value.
+ * @param value the original unfiltered value.
+ * @return the filtered value.
+ */
+float LowpassFilter::filter(float value) {
+
+    float x1old = x1;
+    float x2old = x2;
+    
+    x1 = a11*x1old+a12*x2old+b1*value;
+    x2 = a21*x1old+a22*x2old+b2*value;
+    
+    return frequency*frequency*x1;
+}
+