main.js

    $interval(function() {
      if ($scope.markers[1].lat - $scope.markers[3].lat < 0.00100) {
        $scope.markers[3].lat -= 0.00100;
      }
      if ($scope.markers[3].lng - $scope.markers[1].lng < 0.00050) {
        $scope.markers[3].lng += 0.00050;
      }
    }, 200);