Passing scope data from a function to parent scope?

In my controller I have a $http call which retus a json string which I then want to pass to a directive to be added to a map. The string is being passed from the controller to the directive fine but not from from the $http function within the controller to the directive.

 wmm.controller('wapMapClr', ['$rootScope', '$scope', '$window', '$http', function ($rootScope, $scope, $window, $http) {

$scope.geobj = {};
$scope.geobj.geoprop = ""

// Search by postcode
// create a blank object to hold our form information
$scope.formData = {};
$scope.pcSearch = function () {
$scope.data = {};

$http.post('api/api.php', { postcode: $scope.formData } )
    .success(function (result) {

       $scope.geobj = {geoprop : result.json_string};
      console.log($scope.geobj.geoprop);

Any help would really appreciated. Thanks