GH-337 Android Low Pass Filter (#354)

* Implemented low pass filter as requested by issue 337 * Added value to sample page. * Updated docs for ApplyLowPassFilter * Enabled ApplyLowPassFilter Switch on Android, disabled on all other platforms * Moved LowPassFilter to shared, removed unnecessary usings. * Updated Docs
2018-07-17 22:08:22 +02:00 · 2018-07-17 22:08:22 +02:00 · 56bc8dca66
--- a/Samples/Samples/View/CompassPage.xaml
+++ b/Samples/Samples/View/CompassPage.xaml
@ -11,6 +11,12 @@
    <StackLayout>
        <Label Text="Monitor compass for changes." FontAttributes="Bold" Margin="12" />

+        <Switch IsToggled="{Binding CompassApplyLowPassFilter}" >
+            <Switch.IsVisible>
+                <OnPlatform x:TypeArguments="x:Boolean" Android="True" Default="False"/>
+            </Switch.IsVisible>
+        </Switch>
+
        <ScrollView>
            <Grid Padding="12,0,12,12">
                <Grid.RowDefinitions>
--- a/Samples/Samples/ViewModel/CompassViewModel.cs
+++ b/Samples/Samples/ViewModel/CompassViewModel.cs
@ -10,6 +10,7 @@ namespace Samples.ViewModel
    {
        bool compass1IsActive;
        bool compass2IsActive;
+        bool compassApplyLowPassFilter;
        double compass1;
        double compass2;
        int speed1 = 2;
@ -43,6 +44,16 @@ namespace Samples.ViewModel
            set => SetProperty(ref compass2IsActive, value);
        }

+        public bool CompassApplyLowPassFilter
+        {
+            get => compassApplyLowPassFilter;
+            set
+            {
+                SetProperty(ref compassApplyLowPassFilter, value);
+                Compass.ApplyLowPassFilter = value;
+            }
+        }
+
        public double Compass1
        {
            get => compass1;
--- a/Xamarin.Essentials/Compass/Compass.android.cs
+++ b/Xamarin.Essentials/Compass/Compass.android.cs
@ -54,6 +54,7 @@ namespace Xamarin.Essentials

    class SensorListener : Java.Lang.Object, ISensorEventListener, IDisposable
    {
+        LowPassFilter filter = new LowPassFilter();
        float[] lastAccelerometer = new float[3];
        float[] lastMagnetometer = new float[3];
        bool lastAccelerometerSet;
@ -92,6 +93,11 @@ namespace Xamarin.Essentials
                SensorManager.GetRotationMatrix(r, null, lastAccelerometer, lastMagnetometer);
                SensorManager.GetOrientation(r, orientation);
                var azimuthInRadians = orientation[0];
+                if (Compass.ApplyLowPassFilter)
+                {
+                    filter.Add(azimuthInRadians);
+                    azimuthInRadians = filter.Average();
+                }
                var azimuthInDegress = (Java.Lang.Math.ToDegrees(azimuthInRadians) + 360.0) % 360.0;

                var data = new CompassData(azimuthInDegress);
--- a/Xamarin.Essentials/Compass/Compass.shared.cs
+++ b/Xamarin.Essentials/Compass/Compass.shared.cs
@ -1,5 +1,4 @@
 using System;
-using System.Threading;

 namespace Xamarin.Essentials
 {
@ -11,6 +10,8 @@ namespace Xamarin.Essentials

        public static bool IsMonitoring { get; private set; }

+        public static bool ApplyLowPassFilter { get; set; }
+
        public static void Start(SensorSpeed sensorSpeed)
        {
            if (!IsSupported)
--- a/Xamarin.Essentials/Compass/LowPassFilter.shared.cs
+++ b/Xamarin.Essentials/Compass/LowPassFilter.shared.cs
@ -0,0 +1,39 @@
+using System;
+using System.Collections.Generic;
+
+namespace Xamarin.Essentials
+{
+    class LowPassFilter
+    {
+        const int length = 10;
+
+        float sin;
+        float cos;
+        Queue<float> history = new Queue<float>(length);
+
+        internal void Add(float radians)
+        {
+            sin += (float)Math.Sin(radians);
+
+            cos += (float)Math.Cos(radians);
+
+            history.Enqueue(radians);
+
+            if (history.Count > length)
+            {
+                var old = history.Dequeue();
+
+                sin -= (float)Math.Sin(old);
+
+                cos -= (float)Math.Cos(old);
+            }
+        }
+
+        internal float Average()
+        {
+            var size = history.Count;
+
+            return (float)Math.Atan2(sin / size, cos / size);
+        }
+    }
+}
--- a/docs/en/FrameworksIndex/xamarin-essentials-android.xml
+++ b/docs/en/FrameworksIndex/xamarin-essentials-android.xml
@ -67,6 +67,7 @@
      <Member Id="E:Xamarin.Essentials.Compass.ReadingChanged" />
      <Member Id="M:Xamarin.Essentials.Compass.Start(Xamarin.Essentials.SensorSpeed)" />
      <Member Id="M:Xamarin.Essentials.Compass.Stop" />
+      <Member Id="P:Xamarin.Essentials.Compass.ApplyLowPassFilter" />
      <Member Id="P:Xamarin.Essentials.Compass.IsMonitoring" />
    </Type>
    <Type Name="Xamarin.Essentials.CompassChangedEventArgs" Id="T:Xamarin.Essentials.CompassChangedEventArgs">
--- a/docs/en/FrameworksIndex/xamarin-essentials-ios.xml
+++ b/docs/en/FrameworksIndex/xamarin-essentials-ios.xml
@ -67,6 +67,7 @@
      <Member Id="E:Xamarin.Essentials.Compass.ReadingChanged" />
      <Member Id="M:Xamarin.Essentials.Compass.Start(Xamarin.Essentials.SensorSpeed)" />
      <Member Id="M:Xamarin.Essentials.Compass.Stop" />
+      <Member Id="P:Xamarin.Essentials.Compass.ApplyLowPassFilter" />
      <Member Id="P:Xamarin.Essentials.Compass.IsMonitoring" />
      <Member Id="P:Xamarin.Essentials.Compass.ShouldDisplayHeadingCalibration" />
    </Type>
--- a/docs/en/FrameworksIndex/xamarin-essentials-uwp.xml
+++ b/docs/en/FrameworksIndex/xamarin-essentials-uwp.xml
@ -67,6 +67,7 @@
      <Member Id="E:Xamarin.Essentials.Compass.ReadingChanged" />
      <Member Id="M:Xamarin.Essentials.Compass.Start(Xamarin.Essentials.SensorSpeed)" />
      <Member Id="M:Xamarin.Essentials.Compass.Stop" />
+      <Member Id="P:Xamarin.Essentials.Compass.ApplyLowPassFilter" />
      <Member Id="P:Xamarin.Essentials.Compass.IsMonitoring" />
    </Type>
    <Type Name="Xamarin.Essentials.CompassChangedEventArgs" Id="T:Xamarin.Essentials.CompassChangedEventArgs">
--- a/docs/en/FrameworksIndex/xamarin-essentials.xml
+++ b/docs/en/FrameworksIndex/xamarin-essentials.xml
@ -67,6 +67,7 @@
      <Member Id="E:Xamarin.Essentials.Compass.ReadingChanged" />
      <Member Id="M:Xamarin.Essentials.Compass.Start(Xamarin.Essentials.SensorSpeed)" />
      <Member Id="M:Xamarin.Essentials.Compass.Stop" />
+      <Member Id="P:Xamarin.Essentials.Compass.ApplyLowPassFilter" />
      <Member Id="P:Xamarin.Essentials.Compass.IsMonitoring" />
    </Type>
    <Type Name="Xamarin.Essentials.CompassChangedEventArgs" Id="T:Xamarin.Essentials.CompassChangedEventArgs">
--- a/docs/en/Xamarin.Essentials/Compass.xml
+++ b/docs/en/Xamarin.Essentials/Compass.xml
@ -17,6 +17,26 @@
    </remarks>
  </Docs>
  <Members>
+    <Member MemberName="ApplyLowPassFilter">
+      <MemberSignature Language="C#" Value="public static bool ApplyLowPassFilter { get; set; }" />
+      <MemberSignature Language="ILAsm" Value=".property bool ApplyLowPassFilter" />
+      <MemberSignature Language="DocId" Value="P:Xamarin.Essentials.Compass.ApplyLowPassFilter" />
+      <MemberType>Property</MemberType>
+      <AssemblyInfo>
+        <AssemblyName>Xamarin.Essentials</AssemblyName>
+        <AssemblyVersion>1.0.0.0</AssemblyVersion>
+      </AssemblyInfo>
+      <ReturnValue>
+        <ReturnType>System.Boolean</ReturnType>
+      </ReturnValue>
+      <Docs>
+        <summary>Applies a moving average filter on the Android implementation. Unused on other platforms</summary>
+        <value>If a low pass filter is applied</value>
+        <remarks>
+          <para></para>
+        </remarks>
+      </Docs>
+    </Member>
    <Member MemberName="IsMonitoring">
      <MemberSignature Language="C#" Value="public static bool IsMonitoring { get; }" />
      <MemberSignature Language="ILAsm" Value=".property bool IsMonitoring" />