Android Open Source - Android-Sessions Compass View

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License

The source code is released under:

MIT License

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Java Source Code

package uk.ac.icappsoc.appsocthree.compass;
//  w w w  .  j a va 2s.c  o  m
import android.content.Context;
import android.graphics.Canvas;
import android.util.AttributeSet;
import android.widget.ImageView;

/** The simplest compass - a rotating ImageView. */
public class CompassView extends ImageView {

  private float azimuth;
  
  public CompassView(Context context, AttributeSet attrs) {
    super(context, attrs);
  }
  
  /**
   * Updates the compass, but performs a simple low-pass filter on the input.<p>
   * Note that this causes the compass to jump around when the provided angle wraps.
   * @param newAzimuth relative to magnetic north, in degrees.
   * @param alpha dumb low-pass filter coefficient. 0 - no damping, immediate change; 1 - absolute damping, no change.
   */
  public void setAzimuthDamped(float newAzimuth, float alpha){
    azimuth = alpha * azimuth + (1 - alpha) * newAzimuth;

    // Re-draw ourselves!
    invalidate();
  }
  
  /**
   * Updates the compass, performing a simple IIR filter of order 1
   * and ensuring wrapping angle values do not cause jumpiness.
   * @param newAzimuth relative to magnetic north, in degrees.
   * @param alpha IIR filter coefficient, 0->1. Lower values give smoother response but greater phase lag.
   */
  public void setAzimuthDampedSmart(float newAzimuth, float alpha){
    float diff = newAzimuth - azimuth;
    
    /*
     * When we pass the wrap-around boundary for angular values,
     * Math.abs(difference) will be greater than 180.
     * Catch that, and handle it such that we have smooth angle transitions.
     */
    while(diff >= 180) diff -= 360;
    while(diff < -180) diff += 360;
    
    azimuth += alpha * diff;
    
    // Do same as above for the resulting angle.
    while(azimuth >= 180) azimuth -= 360;
    while(azimuth < -180) azimuth += 360;
    
    // Re-draw ourselves!
    invalidate();
  }
  
  @Override
  public void onDraw(Canvas canvas){
    canvas.save();
    canvas.rotate(-azimuth, getWidth() / 2, getHeight() / 2);
    super.onDraw(canvas);
    canvas.restore();
  }

}

Java Source Code List