FIR FIlter

OxyPlotExample/GettingStarted/Documentation/FIRFilter.md

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+# FIR Low Pass Filter 개요
+
+- 샘플링 주파수 ($f_s$: Sampling Frequency)
+    - 신호를 샘플링 하는 속도
+- 컷오프 주파수 ($f_c$: Cutoff Frequency)
+    - 필터의 신호를 통과시키거나 차단하기 시작하는 주파수
+- 필터 계수 설계
+    - 필터의 특성을 정의하는 계수. 해밍 창(Hamming Window)등을 이용해 설계
+- 페이즈 지연 보상
+    - 필터로 인한 지연 보상

OxyPlotExample/GettingStarted/Filter/FIRFilter.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace GettingStarted.Filter
+{
+    internal class FIRFilter
+    {
+        private double[] _coefficients;
+        private double[] _buffer;
+        private int _bufferIndex;
+        private int _delay;
+
+        public FIRFilter(double[] coefficients)
+        {
+            _coefficients = coefficients;
+            _buffer = new double[coefficients.Length];
+            _bufferIndex = 0;
+            _delay = (_coefficients.Length - 1) / 2;
+        }
+
+        public double Process(double input)
+        {
+            _buffer[_bufferIndex] = input;
+            double result = 0d;
+
+            int index = _bufferIndex;
+            for (int i = 0; i < _coefficients.Length; i++)
+            {
+                result += _coefficients[i] * _buffer[index];
+                index = (index > 0) ? index - 1 : _buffer.Length - 1;
+            }
+
+            _bufferIndex = (_bufferIndex + 1) % _buffer.Length;
+
+            return result;
+        }
+
+        public double[] ProcessSignal(double[] inputSignal)
+        {
+            int signalLength = inputSignal.Length;
+            double[] outputSignal = new double[signalLength];
+
+            for (int i = 0; i < signalLength; i++)
+            {
+                outputSignal[i] = Process(inputSignal[i]);
+            }
+
+            // 페이즈 지연 보상
+            for (int i = 0; i < signalLength; i++)
+            {
+                if (i + _delay < signalLength)
+                {
+                    outputSignal[i] = outputSignal[i + _delay];
+                }
+                else
+                {
+                    outputSignal[i] = 0; // 지연 보상 후 남은 부분은 0으로 채움
+                }
+            }
+
+            return outputSignal;
+        }
+
+        public static double[] DesignLowPassFilter(int length, double cutoffFrequnecy, double sampleRate)
+        {
+            double[] coefficients = new double[length];
+            double omega_c = 2 * Math.PI * cutoffFrequnecy / sampleRate;
+            int M = length - 1;
+
+            for (int n = 0; n <= M; n++)
+            {
+                if (n - M / 2 == 0)
+                {
+                    coefficients[n] = omega_c / Math.PI;
+                }
+                else
+                {
+                    coefficients[n] = Math.Sin(omega_c * (n - M / 2)) / (Math.PI * (n - M / 2)) * (0.54 - 0.46 * Math.Cos(2 * Math.PI * n / M));
+                }
+            }
+
+            return coefficients;
+        }
+    }
+}

OxyPlotExample/GettingStarted/GettingStarted.csproj

@@ -14,8 +14,4 @@
     <PackageReference Include="OxyPlot.Wpf" Version="2.1.2" />
   </ItemGroup>
 
-  <ItemGroup>
-    <Folder Include="Documentation\" />
-  </ItemGroup>
-
 </Project>

OxyPlotExample/GettingStarted/MainWindow.xaml

@@ -8,9 +8,13 @@
         Title="MainWindow"
         Width="800"
         Height="450"
-        mc:Ignorable="d"
-        Closing="Window_Closing">
+        Closing="Window_Closing"
+        mc:Ignorable="d">
     <Grid>
+        <Grid.ColumnDefinitions>
+            <ColumnDefinition Width="*" />
+            <ColumnDefinition Width="3*" />
+        </Grid.ColumnDefinitions>
         <Grid.RowDefinitions>
             <RowDefinition Height="*" />
             <RowDefinition Height="*" />
@@ -19,6 +23,8 @@
 
         <views:MainViewControl Grid.Row="0" />
         <views:MainViewControl2 Grid.Row="1" />
-        <views:MainViewControl3 Grid.Row="2" x:Name="vcRT"/>
+        <views:MainViewControl3 x:Name="vcRT" Grid.Row="2" />
+
+        <views:FIRFilterView Grid.Column="1" Grid.RowSpan="3" />
     </Grid>
 </Window>

OxyPlotExample/GettingStarted/ViewModels/FIRFilterViewModel.cs

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+using CommunityToolkit.Mvvm.ComponentModel;
+using CommunityToolkit.Mvvm.Input;
+using GettingStarted.Filter;
+using OxyPlot;
+using OxyPlot.Series;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace GettingStarted.ViewModels
+{
+    internal partial class FIRFilterViewModel : ObservableObject
+    {
+
+        [ObservableProperty]
+        private PlotModel _myModel;
+
+
+        [ObservableProperty]
+        private LineSeries _inputSeries;
+
+
+        [ObservableProperty]
+        private LineSeries _outputSeries;
+
+        [ObservableProperty]
+        private double _sampleRate;
+
+
+        [ObservableProperty]
+        private double _cutoffFrequency;
+
+
+        [ObservableProperty]
+        private int _filterLength;
+
+        double[] _coefficients;
+
+        FIRFilter _filter;
+
+        double[] _inputSignal;
+
+        double _noiseLevel = 0.3;
+        public FIRFilterViewModel()
+        {
+            MyModel = new PlotModel() { Title = "FIR Low Pass Filter" };
+            InputSeries = new LineSeries() { Title = "Input" };
+            OutputSeries = new LineSeries() { Title = "Output" };
+            MyModel.Series.Add(InputSeries);
+            MyModel.Series.Add(OutputSeries);
+
+            SampleRate = 1000d;
+            CutoffFrequency = 100d;
+            FilterLength = 21;
+
+            Random rand = new Random();
+            List<double> inputSimulate = new List<double>();
+            int x = 0;
+            for (int i = 0; i < 100; i++)
+            {
+                double noise = (rand.NextDouble() - 0.5) * _noiseLevel;
+                double value = Math.Sin(x++ * 0.1) + noise;
+                inputSimulate.Add(value);
+            }
+
+            _inputSignal = inputSimulate.ToArray(); ;
+
+            ProcessSignal();
+        }
+
+        [RelayCommand]
+        private void ProcessSignal()
+        {
+            _coefficients = FIRFilter.DesignLowPassFilter(FilterLength, CutoffFrequency, SampleRate);
+            _filter = new FIRFilter(_coefficients);
+
+            double[] outputSignal = _filter.ProcessSignal(_inputSignal);
+
+            {
+                InputSeries.Points.Clear();
+                int x = 0;
+                DataPoint[] dataPoints = _inputSignal.Select(val => new DataPoint(++x, val)).ToArray();
+                InputSeries.Points.AddRange(dataPoints);
+            }
+
+            {
+                OutputSeries.Points.Clear();
+                int x = 0;
+                DataPoint[] dataPoints = outputSignal.Select(val => new DataPoint(++x, val)).ToArray();
+                OutputSeries.Points.AddRange(dataPoints);
+            }
+
+            MyModel.InvalidatePlot(true);
+        }
+    }
+}

OxyPlotExample/GettingStarted/Views/FIRFilterView.xaml

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+<UserControl x:Class="GettingStarted.Views.FIRFilterView"
+             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+             xmlns:local="clr-namespace:GettingStarted.Views"
+             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+             xmlns:oxy="http://oxyplot.org/wpf"
+             xmlns:viewModels="clr-namespace:GettingStarted.ViewModels"
+             d:DesignHeight="450"
+             d:DesignWidth="800"
+             mc:Ignorable="d">
+    <UserControl.DataContext>
+        <viewModels:FIRFilterViewModel />
+    </UserControl.DataContext>
+    <Grid>
+        <Grid.ColumnDefinitions>
+            <ColumnDefinition Width="*" />
+            <ColumnDefinition Width="250" />
+        </Grid.ColumnDefinitions>
+
+        <oxy:PlotView Model="{Binding MyModel}" />
+
+        <StackPanel Grid.Column="1" Orientation="Vertical">
+            <StackPanel Orientation="Horizontal">
+                <Label Width="150" Content="SampleRate" />
+                <TextBox Width="80" Text="{Binding SampleRate}" />
+            </StackPanel>
+            <StackPanel Orientation="Horizontal">
+                <Label Width="150" Content="CutoffFrequency" />
+                <TextBox Width="80" Text="{Binding CutoffFrequency}" />
+            </StackPanel>
+            <StackPanel Orientation="Horizontal">
+                <Label Width="150" Content="FilterLength" />
+                <TextBox Width="80" Text="{Binding FilterLength}" />
+            </StackPanel>
+            <Button Command="{Binding ProcessSignalCommand}" Content="Simulate" />
+        </StackPanel>
+    </Grid>
+</UserControl>

OxyPlotExample/GettingStarted/Views/FIRFilterView.xaml.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using System.Windows;
+using System.Windows.Controls;
+using System.Windows.Data;
+using System.Windows.Documents;
+using System.Windows.Input;
+using System.Windows.Media;
+using System.Windows.Media.Imaging;
+using System.Windows.Navigation;
+using System.Windows.Shapes;
+
+namespace GettingStarted.Views
+{
+    /// <summary>
+    /// FIRFilterView.xaml에 대한 상호 작용 논리
+    /// </summary>
+    public partial class FIRFilterView : UserControl
+    {
+        public FIRFilterView()
+        {
+            InitializeComponent();
+        }
+    }
+}