Android How to - Display the compass direction

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The following code shows how to .

Example

Main layout activity_main.xml file

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="fill_parent"
  android:layout_height="fill_parent">
  <TextView
    android:id="@+id/direction"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_centerInParent="true"
    android:textSize="64dip"
    android:textStyle="bold"
  />
  <TextView  
    android:id="@+id/values"
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content"
    android:layout_alignParentBottom="true"
  />
</RelativeLayout>

Main activity Java code

package com.java2s.myapplication3.app;
// w w w  .  ja  va2  s  . com
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 MainActivity extends Activity implements SensorEventListener {

    //Allocate data arrays once and reuse
    float[] temp = new float[9];
    float[] rotation = new float[9];
    float[] values = new float[3];

    private SensorManager mSensorManager;
    private Sensor mAccelerometer, mField;
    private TextView valueView, directionView;

    private float[] mGravity = new float[3];
    private float[] mMagnetic = new float[3];

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mSensorManager = (SensorManager) getSystemService(SENSOR_SERVICE);
        mAccelerometer = mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
        mField = mSensorManager.getDefaultSensor(Sensor.TYPE_MAGNETIC_FIELD);

        valueView = (TextView) findViewById(R.id.values);
        directionView = (TextView) findViewById(R.id.direction);
    }

    protected void onResume() {
        super.onResume();
        mSensorManager.registerListener(this, mAccelerometer, SensorManager.SENSOR_DELAY_UI);
        mSensorManager.registerListener(this, mField, SensorManager.SENSOR_DELAY_UI);
    }

    protected void onPause() {
        super.onPause();
        mSensorManager.unregisterListener(this);
    }

    private void updateDirection() {
        SensorManager.getRotationMatrix(temp, null, mGravity, mMagnetic);
        SensorManager.remapCoordinateSystem(temp, SensorManager.AXIS_X, SensorManager.AXIS_Z, rotation);
        SensorManager.getOrientation(rotation, values);
        for (int i = 0; i < values.length; i++) {
            Double degrees = (values[i] * 180) / Math.PI;
            values[i] = degrees.floatValue();
        }
        directionView.setText(getDirectionFromDegrees(values[0]));
        valueView.setText(String.format("Azimuth: %1$1.2f, Pitch: %2$1.2f, Roll: %3$1.2f",
                values[0], values[1], values[2]));
    }

    private String getDirectionFromDegrees(float degrees) {
        if (degrees >= -22.5 && degrees < 22.5) {
            return "N";
        }
        if (degrees >= 22.5 && degrees < 67.5) {
            return "NE";
        }
        if (degrees >= 67.5 && degrees < 112.5) {
            return "E";
        }
        if (degrees >= 112.5 && degrees < 157.5) {
            return "SE";
        }
        if (degrees >= 157.5 || degrees < -157.5) {
            return "S";
        }
        if (degrees >= -157.5 && degrees < -112.5) {
            return "SW";
        }
        if (degrees >= -112.5 && degrees < -67.5) {
            return "W";
        }
        if (degrees >= -67.5 && degrees < -22.5) {
            return "NW";
        }

        return null;
    }

    public void onAccuracyChanged(Sensor sensor, int accuracy) {
    }

    public void onSensorChanged(SensorEvent event) {
        switch (event.sensor.getType()) {
            case Sensor.TYPE_ACCELEROMETER:
                System.arraycopy(event.values, 0, mGravity, 0, event.values.length);
                break;
            case Sensor.TYPE_MAGNETIC_FIELD:
                System.arraycopy(event.values, 0, mMagnetic, 0, event.values.length);
                break;
            default:
                return;
        }

        if (mGravity != null && mMagnetic != null) {
            updateDirection();
        }
    }
}

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