Shared data between controllers using factory and promises - angularjs

Question

Ok so there is a lot out there about sharing data between controllers using factory/service, but I'm not finding what applies to my issue. Either I'm interpreting the answers incorrectly or this is a valid question I'm about to ask! Hopefully the latter.
I would like controller 2 to recognize when a new http call has been made and the factory images object has been updated. at the moment it resolves once and then ignores any subsequent updates. What am i overlooking?
My view:
<div>
<ul class="dynamic-grid" angular-grid="pics" grid-width="150" gutter-size="0" angular-grid-id="gallery" refresh-on-img-load="false" >
<li data-ng-repeat="pic in pics" class="grid" data-ng-clock>
<img src="{{pic.image.low_res.url}}" class="grid-img" data-actual-width = "{{pic.image.low_res.width}}" data-actual-height="{{pic.image.low_res.height}}" />
</li>
</ul>
</div>
factory:
.factory('imageService',['$q','$http',function($q,$http){
var images = {}
var imageServices = {};
imageServices.homeImages = function(){
console.log('fire home images')
images = $http({
method: 'GET',
url: '/api/insta/geo',
params: homeLoc
})
};
imageServices.locImages = function(placename){
console.log('fire locImages')
images = $http({
method: 'GET',
url: '/api/geo/loc',
params: placename
})
};
imageServices.getImages = function(){
console.log('fire get images', images)
return images;
}
return imageServices;
}]);
controller1:
angular.module('trailApp.intro', [])
.controller('introCtrl', function($scope, $location, $state, showTrails, imageService) {
// run the images service so the background can load
imageService.homeImages();
var intro = this;
intro.showlist = false;
intro.data = [];
//to get all the trails based on user's selected city and state (collected in the location object that's passed in)
intro.getList = function(location) {
intro.city = capitalize(location.city);
intro.state = capitalize(location.state);
//get placename for bg
var placename = {placename: intro.city + ',' + intro.state};
imageService.locImages(placename);
... do other stuff...
controller2:
angular.module('trailApp.bkgd', [])
.controller('bkgdCtrl', ['$scope','imageService', 'angularGridInstance', function ($scope,imageService, angularGridInstance) {
$scope.pics = {};
imageService.getImages().then(function(data){
$scope.pics = data;
console.log($scope.pics);
});
}]);

Answer 1

Your controller2 implementation only got the images once, you probably need a $watch to keep to updated:
angular.module('trailApp.bkgd', [])
.controller('bkgdCtrl', ['$scope','imageService', 'angularGridInstance', function ($scope,imageService, angularGridInstance) {
$scope.pics = {};
$scope.$watch(function(){
return imageService.getImages(); // This returns a promise
}, function(images, oldImages){
if(images !== oldImages){ // According to your implementation, your images promise changes reference
images.then(function(data){
$scope.pics = data;
console.log($scope.pics);
});
}
});
}]);