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Sunday, January 9, 2011

Using orientation sensors: Simple Compass sample

In this post we will show how to get the sensor informatiĆ³n of the device to do a simple compass application.

Getting the magnetic orientation with the TYPE_ORIENTATION sensor is deprecated, and now you must subscribe to TYPE_ACCELEROMETER and TYPE_MAGNETIC_FIELD to get the correct orientation. This way is a little tricky, but with this sample you will get it very easy.

This is the code for an activity that shows in a canvas a simple compass:


package com.samplecompass;
import android.app.Activity;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Paint.Style;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.os.Bundle;
import android.view.View;

public class CompassActivity extends Activity implements SensorEventListener {

Float azimut; // View to draw a compass

public class CustomDrawableView extends View {
Paint paint = new Paint();
public CustomDrawableView(Context context) {
super(context);
paint.setColor(0xff00ff00);
paint.setStyle(Style.STROKE);
paint.setStrokeWidth(2);
paint.setAntiAlias(true);
};

protected void onDraw(Canvas canvas) {
int width = getWidth();
int height = getHeight();
int centerx = width/2;
int centery = height/2;
canvas.drawLine(centerx, 0, centerx, height, paint);
canvas.drawLine(0, centery, width, centery, paint);
// Rotate the canvas with the azimut
if (azimut != null)
canvas.rotate(-azimut*360/(2*3.14159f), centerx, centery);
paint.setColor(0xff0000ff);
canvas.drawLine(centerx, -1000, centerx, +1000, paint);
canvas.drawLine(-1000, centery, 1000, centery, paint);
canvas.drawText("N", centerx+5, centery-10, paint);
canvas.drawText("S", centerx-10, centery+15, paint);
paint.setColor(0xff00ff00);
}
}

CustomDrawableView mCustomDrawableView;
private SensorManager mSensorManager;
Sensor accelerometer;
Sensor magnetometer;

protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mCustomDrawableView = new CustomDrawableView(this);
setContentView(mCustomDrawableView); // Register the sensor listeners
mSensorManager = (SensorManager)getSystemService(SENSOR_SERVICE);
accelerometer = mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
magnetometer = mSensorManager.getDefaultSensor(Sensor.TYPE_MAGNETIC_FIELD);
}

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

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

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

float[] mGravity;
float[] mGeomagnetic;
public void onSensorChanged(SensorEvent event) {
if (event.sensor.getType() == Sensor.TYPE_ACCELEROMETER)
mGravity = event.values;
if (event.sensor.getType() == Sensor.TYPE_MAGNETIC_FIELD)
mGeomagnetic = event.values;
if (mGravity != null && mGeomagnetic != null) {
float R[] = new float[9];
float I[] = new float[9];
boolean success = SensorManager.getRotationMatrix(R, I, mGravity, mGeomagnetic);
if (success) {
float orientation[] = new float[3];
SensorManager.getOrientation(R, orientation);
azimut = orientation[0]; // orientation contains: azimut, pitch and roll
}
}
mCustomDrawableView.invalidate();
}
}

I hope It will be useful for you.


Note: This is real code from Trackeen: your Mushrooms and Fishing GPS.