Create our Android Compass

Base on last post "Detect Orientation using Accelerometer and Magnetic Field sensors", a Android compass is implemented here. In the implementation, the final result (base on Accelerometer and Magnetic Field sensors) is show in RED, point to the north.



Create a custom View, Compass, extends View. The method update() is called from onSensorChanged() of main activity, with the updated direction.

package com.AndroidDetOrientation;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.View;

public class Compass extends View {

 private float direction;
 
 public Compass(Context context) {
  super(context);
  // TODO Auto-generated constructor stub
 }

 public Compass(Context context, AttributeSet attrs) {
  super(context, attrs);
  // TODO Auto-generated constructor stub
 }

 public Compass(Context context, AttributeSet attrs, int defStyle) {
  super(context, attrs, defStyle);
  // TODO Auto-generated constructor stub
 }

 @Override
 protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
  setMeasuredDimension(
    MeasureSpec.getSize(widthMeasureSpec),
    MeasureSpec.getSize(heightMeasureSpec));
 }

 @Override
 protected void onDraw(Canvas canvas) {
  
  int w = getMeasuredWidth();
  int h = getMeasuredHeight();
  int r;
  if(w > h){
   r = h/2;
  }else{
   r = w/2;
  }
  
  Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
  paint.setStyle(Paint.Style.STROKE);
  paint.setStrokeWidth(5);
  paint.setColor(Color.WHITE);
  
  canvas.drawCircle(w/2, h/2, r, paint);
  
  paint.setColor(Color.RED);
  canvas.drawLine(
    w/2,
    h/2,
    (float)(w/2 + r * Math.sin(-direction)),
    (float)(h/2 - r * Math.cos(-direction)),
    paint);

 }
 
 public void update(float dir){
  direction = dir;
  invalidate();
 }
 
}

Modify main activity, AndroidDetOrientationActivity, to update Compass.

package com.AndroidDetOrientation;

import android.app.Activity;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.os.Bundle;
import android.widget.TextView;

public class AndroidDetOrientationActivity extends Activity
 implements SensorEventListener{
 
 SensorManager sensorManager;
 private Sensor sensorAccelerometer;
 private Sensor sensorMagneticField;
 
 private float[] valuesAccelerometer;
 private float[] valuesMagneticField;
 
 private float[] matrixR;
 private float[] matrixI;
 private float[] matrixValues;
 
 TextView readingAzimuth, readingPitch, readingRoll;
 Compass myCompass;
 
  /** Called when the activity is first created. */
  @Override
  public void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.main);
      readingAzimuth = (TextView)findViewById(R.id.azimuth);
      readingPitch = (TextView)findViewById(R.id.pitch);
      readingRoll = (TextView)findViewById(R.id.roll);
    
      myCompass = (Compass)findViewById(R.id.mycompass);
    
      sensorManager = (SensorManager)getSystemService(SENSOR_SERVICE);
      sensorAccelerometer = sensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
   sensorMagneticField = sensorManager.getDefaultSensor(Sensor.TYPE_MAGNETIC_FIELD);
    
   valuesAccelerometer = new float[3];
   valuesMagneticField = new float[3];

   matrixR = new float[9];
   matrixI = new float[9];
   matrixValues = new float[3];
  }

 @Override
 protected void onResume() {

  sensorManager.registerListener(this,
    sensorAccelerometer,
    SensorManager.SENSOR_DELAY_NORMAL);
  sensorManager.registerListener(this,
    sensorMagneticField,
    SensorManager.SENSOR_DELAY_NORMAL);
  super.onResume();
 }

 @Override
 protected void onPause() {

  sensorManager.unregisterListener(this,
    sensorAccelerometer);
  sensorManager.unregisterListener(this,
    sensorMagneticField);
  super.onPause();
 }

 @Override
 public void onAccuracyChanged(Sensor arg0, int arg1) {
  // TODO Auto-generated method stub
  
 }

 @Override
 public void onSensorChanged(SensorEvent event) {
  // TODO Auto-generated method stub
  
  switch(event.sensor.getType()){
  case Sensor.TYPE_ACCELEROMETER:
   for(int i =0; i < 3; i++){
    valuesAccelerometer[i] = event.values[i];
   }
   break;
  case Sensor.TYPE_MAGNETIC_FIELD:
   for(int i =0; i < 3; i++){
    valuesMagneticField[i] = event.values[i];
   }
   break;
  }
  
  boolean success = SensorManager.getRotationMatrix(
       matrixR,
       matrixI,
       valuesAccelerometer,
       valuesMagneticField);
  
  if(success){
   SensorManager.getOrientation(matrixR, matrixValues);
   
   double azimuth = Math.toDegrees(matrixValues[0]);
   double pitch = Math.toDegrees(matrixValues[1]);
   double roll = Math.toDegrees(matrixValues[2]);
   
   readingAzimuth.setText("Azimuth: " + String.valueOf(azimuth));
   readingPitch.setText("Pitch: " + String.valueOf(pitch));
   readingRoll.setText("Roll: " + String.valueOf(roll));
   
   myCompass.update(matrixValues[0]);
  }
  
 }
}

Modify main.xml to add a View of Compass.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="fill_parent"
  android:layout_height="fill_parent"
  android:orientation="vertical" >

  <TextView
      android:layout_width="fill_parent"
      android:layout_height="wrap_content"
      android:text="@string/hello" />
  <TextView
      android:id="@+id/azimuth"
      android:layout_width="fill_parent"
      android:layout_height="wrap_content"/>
  <TextView
      android:id="@+id/pitch"
      android:layout_width="fill_parent"
      android:layout_height="wrap_content"/>
  <TextView
      android:id="@+id/roll"
      android:layout_width="fill_parent"
      android:layout_height="wrap_content"/>
  <view
      class="com.AndroidDetOrientation.Compass"
      android:id="@+id/mycompass"
      android:layout_width="fill_parent"
      android:layout_height="fill_parent"/>

</LinearLayout>