fix alpha formula

OxyPlotExample/GettingStarted/Filter/HighPassFilter.cs

@@ -12,12 +12,14 @@ namespace GettingStarted.Filter
         private double _previousOutput;
         private double _previouseInput;
 
-        public HighPassFilter(double alpha)
+        public HighPassFilter(double cutoffFreq, double dt)
         {
-            if (alpha < 0.0 || alpha > 1.0)
-                throw new ArgumentException(nameof(alpha), "Alpha must be between 0 and 1.");
+            if (cutoffFreq <= 0.0 || dt <= 0.0)
+                throw new ArgumentException("Cutoff frequency and dt must be greater than 0.");
+
+            double rc = 1.0 / (2 * Math.PI * cutoffFreq);
+            _alpha = rc / (rc + dt);
 
-            _alpha = alpha;
             _previousOutput = 0.0;
             _previouseInput = 0.0;
         }

OxyPlotExample/GettingStarted/Filter/LowPassFilter.cs

@@ -11,12 +11,14 @@ namespace GettingStarted.Filter
         private double _alpha;
         private double _previousOutput;
 
-        public LowPassFilter(double alpha)
+        public LowPassFilter(double cutoffFreq, double dt)
         {
-            if (alpha < 0.0 || alpha > 1.0)
-                throw new ArgumentException(nameof(alpha), "Alpha must be between 0 and 1.");
+            if (cutoffFreq <= 0.0 || dt <= 0.0)
+                throw new ArgumentException("Cutoff frequency and dt must be greater than 0.");
+
+            double rc = 1.0 / (2 * Math.PI * cutoffFreq);
+            _alpha = dt / (rc + dt);
 
-            _alpha = alpha;
             _previousOutput = 0.0;
         }
 

OxyPlotExample/GettingStarted/ViewModels/MainViewModel3.cs

@@ -16,6 +16,8 @@ namespace GettingStarted.ViewModels
 {
     internal partial class MainViewModel3 : ObservableObject
     {
+        private readonly double DT = 0.01;
+
         [ObservableProperty]
         private PlotModel _myModel;
 
@@ -40,7 +42,7 @@ namespace GettingStarted.ViewModels
             LineSeries = new LineSeries() { Title = "Dynamic Data" };
             LpfSeries = new LineSeries() { Title = "Filtered" };
 
-            _filter = new HighPassFilter(0.5);
+            _filter = new LowPassFilter(5d, DT);
 
             DateTimeAxis timeAxis = new DateTimeAxis()
             {
@@ -67,7 +69,7 @@ namespace GettingStarted.ViewModels
             CutOffSecond = 10d;
 
             _timer = new System.Timers.Timer();
-            _timer.Interval = 10;
+            _timer.Interval = DT * 1000;
             _timer.Elapsed -= _timer_Elapsed;
             _timer.Elapsed += _timer_Elapsed;
         }