AngularJS $ scope。$ apply与$ q

我在理解某个人能解释一下这段代码之间的区别时遇到了一些麻烦：

app.controller('MainCtrl', function($scope,$http) {
if(navigator.geolocation){
    navigator.geolocation.watchPosition(function(position){ //asychronous
        $scope.$apply(function(){
            $scope.position=position;
       });
   });
};

还有这个

function getPosition(){
  var deferred=$q.defer();
  if(navigator.geolocation){
    navigator.geolocation.watchPosition(function(position){
        deferred.resolve(position);
    })
  }return deferred.promise;
}

var promise=getPosition();
promise.then(function(position){
    $scope.position2=position;
})

谢谢