title: Make compass in React-Native
body: <p>I'am trying to make a compass but i don't know how to use the data of the Magnetometer.</p>
  
  <p>This is my class Compass:</p>
  
  <pre><code>class Compass extends Component {
    constructor(props) {
      super(props);
    }
    componentWillMount(){
      this._animeRotation = new Animated.Value(0);
    }
    componentDidMount() {
        this.startAnimation();
    }
    startAnimation() {
      Animated.timing(this._animeRotation, {
        toValue: this.props.magn, //&lt;-- What put here?
        duration: 1000,
      }).start(() =&gt; {
        this.startAnimation();
      });
    }
    render() {
      var interpolatedRotateAnimation = this._animeRotation.interpolate({
        inputRange: [0, 100],
        outputRange: ['0deg', '360deg']
      });
      return (
        &lt;View&gt;
          &lt;Animated.View style={[styles.box, {transform: [{rotate: interpolatedRotateAnimation}]}]}&gt;
            &lt;Image style={styles.box} source={require('./arrow.png')}&gt;&lt;/Image&gt;
          &lt;/Animated.View&gt;
        &lt;/View&gt;
      );
    }
  }
  </code></pre>
  
  <p>This is the class App:</p>
  
  <pre><code>class App extends Component {
    constructor(props) {
      super(props);
      this.state = {
        magn: {
          x: 0,
          y: 0,
          z: 0
        }
      };
    }
    componentDidMount() {
      //I can get the gyroscope if is necessary
      SensorManager.startMagnetometer(500);
      // magn is a object with axis z,y and x
      DeviceEventEmitter.addListener('Magnetometer', (magn) =&gt; this.setState({magn})); 
    }
    render() {
      return (
        &lt;View&gt;
            &lt;Compass magn={this.state.magn.x}&gt;&lt;/Compass&gt;
        &lt;/View&gt;
      );
    }
  }
  </code></pre>
  
  <p>With this code the arrow rotate but not as it should. That I have to do?</p>