ngModel and resetting value - angularjs

Question

So have two directives that need to share data. Both are under the same controller, so set up the variable $scope.selection to store the selection, it gets a default value in the controller.
knowledge.controller('industryController', function($scope, mwFactory){
$scope.menudata={sections: [
{group: 'FMP', name: 'Finance'},
{group: 'FinTech', name: 'Financial Technology'},
]
}
if ($scope.selection) {
console.log("This is " + $scope.selection)
} else {
$scope.selection = 'Main_Page'
}
})
I then send that to a menu where you can make selection
<nav-circle group="section.group" ng-model="selection"></nav-circle>
I then set it as follows inside the directive
function nodeclick(d){
//console.log("Name is " + d.url);
console.log("Old model is " + ngModel.$modelValue)
ngModel.$modelValue = d.url;
ngModel.$viewValue = d.url;
console.log("New model is " + ngModel.$modelValue)
}
However, it does not seem like it is updating, or potentially even weirder, that something is resetting ngModel.
Got a call further up,
ngModel.$render = function () {
console.log("ngRender got called " + ngModel.$modelValue);
};
And this kicks off every minute or so, and always returns the value to the original value. What am I missing

Answer 1

OK, this may not be the best way, but it works, and sometimes that is enough:)
Instead of sending a variable I sent an object, and I think (someone who knows angular and javascript better may be able to explain/confirm) this means that the directive will be writing to a memory address rather than to a variable. Which also means that the ng-model will not change (the memory address is the same, the data stored at that memory address is changed).
Might be wrong, but the solution works as if that was the case.
So, define the scope variable:
$scope.selection = {};
$scope.selection.default = 'Main_Page'
$scope.selection.current = '';
Then send the following to the directives:
<nav-circle group="section.group" ng-model="selection.current"></nav-circle>
And to change the scope variable in the directive you just set viewValue
ngModel.$setViewValue(d.url);
As I mentioned, I am not certain if this is the right way, or if my understanding is correct, but it works:)