Compass controller

app.js

.controller('compassCtrl', function($scope, $ionicPlatform, Location) {

  $scope.$on('$ionicView.afterLeave', function(){
    console.log("Before leaving clear the compass");
    if(positionTimerId) navigator.geolocation.clearWatch(positionTimerId); 
    if(compassTimerId) navigator.compass.clearWatch(compassTimerId);
  });

  $scope.location = Location.get();
  console.log($scope.location);

  $scope.isError = false;

  var destinationPosition;
  var destinationBearing;

  var positionTimerId;
  var currentPosition;
  var prevPosition;
  var prevPositionError;      

  var compassTimerId;
  var currentHeading;
  var prevHeading;
  var prevCompassErrorCode;

  $scope.initCompass = function(){

      minPositionAccuracy = 50; // Minimum accuracy in metres to accept as a reliable position

      $scope.watchPosition();            
      $scope.watchCompass();

      $scope.updateDestination();
  };

  $scope.watchPosition = function(){

    if(positionTimerId) navigator.geolocation.clearWatch(positionTimerId); 
    positionTimerId = navigator.geolocation.watchPosition($scope.onPositionUpdate, $scope.onPositionError, {
        enableHighAccuracy: true,
        timeout: 1000,
        maxiumumAge: 0
    });

  }

  $scope.watchCompass = function(){
      if(compassTimerId) navigator.compass.clearWatch(compassTimerId);
      compassTimerId = navigator.compass.watchHeading($scope.onCompassUpdate, $scope.onCompassError, {
          frequency: 100 // Update interval in ms
      });
  }

  $scope.onPositionUpdate = function(position){
      if(position.coords.accuracy > minPositionAccuracy) return;

      prevPosition = currentPosition;
      currentPosition = new LatLon(position.coords.latitude, position.coords.longitude);

      $scope.updatePositions();
  }

  $scope.onPositionError = function(error){

      $scope.watchPosition();

      if(prevPositionError && prevPositionError.code == error.code && prevPositionError.message == error.message){
        $scope.isError = false;
        return ;
      }

      $scope.isError = true;
      $scope.errorMessage = "Error while retrieving current position. <br/>Error code: " + error.code + "<br/>Message: " + error.message;

      prevPositionError = {
          code: error.code,
          message: error.message
      };
  }

  $scope.onCompassUpdate = function(heading){
      prevHeading = currentHeading;
      currentHeading = Math.round(heading.magneticHeading);

      if(currentHeading == prevHeading) return;

      $scope.updateHeading();
  }

  function onCompassError(error){
      console.log('COMPASS ERROR');
      console.log(error);
      $scope.watchCompass();

      if(prevCompassErrorCode && prevCompassErrorCode == error.code) return; 

      var errorType;
      switch(error.code){
          case 1:
              errorType = "Compass not supported";
              break;
          case 2:
              errorType = "Compass internal error";
              break;
          default:
              errorType = "Unknown compass error";
      }

      $scope.isError = true;
      $scope.errorMessage = "Error while retrieving compass heading: "+errorType;

      prevCompassErrorCode = error.code;
  }

  $scope.updateDestination = function(){
      destinationPosition = new LatLon($scope.location.lat, $scope.location.lng);
      $scope.updatePositions();
  }       


  $scope.updatePositions = function(){
      if(!currentPosition) return;

      $scope.isError = false;

      destinationBearing = Math.round(currentPosition.bearingTo(destinationPosition)); 

      $scope.distance = Math.round(currentPosition.distanceTo(destinationPosition)*1000);
      $scope.bearing = destinationBearing;

      $scope.updateDifference(); 
  }

  $scope.updateHeading = function(){
      $scope.heading = currentHeading;
      $scope.updateDifference();
  }

  $scope.updateDifference = function(){
      var diff = destinationBearing - currentHeading;
      $scope.difference = diff;
      $scope.animateRotation = "-webkit-transform: rotate("+diff+"deg)";
      $scope.$apply();
  }

  $ionicPlatform.ready(function() {
    $scope.initCompass();
  });

  
});