Publications Subscriptions Observe - meteor

Question

I am working on a project where I want to show markers on a map.
These markers should be published from server with a viewport-constraint. That means that just markers are published which are inside the current users viewport.
The publication looks something like this:
//server
Meteor.publish('posts', function(bottom_left_x, bottom_left_y, upper_right_x, upper_right_y, limit) {
return Posts.find({locs: {$geoWithin: {$box:
[[bottom_left_x, bottom_left_y],
[upper_right_x, upper_right_y]]}}},
{sort: {submitted: -1}, limit: limit});
});
I always call this function via subscription when my map_center changes:
//client
google.maps.event.addListener(map, 'idle', function(event) {
var bounds = map.getBounds();
var ne = bounds.getNorthEast();
var sw = bounds.getSouthWest();
postsHandle= Meteor.subscribe('posts', sw.lat(), sw.lng(), ne.lat(), ne.lng(), 10);
});
Till now everything works fine.
Further i created a observefunction on posts, that renders a marker when "added" is called and remove when "removed" is called. Observe is very good to render new markers and to destroy the old ones
//client
Posts.find().observeChanges({
added: function(post) {
// when 'added' callback fires, add HTML element
var marker = new google.maps.Marker({
position: new google.maps.LatLng(post.locs.lat, post.locs.lng),
postId: post._id,
map: map,
});
},removed .... and so on
That problem is that the observe-Callback is triggered on the whole Posts-Collection. But i just want to show markers which are inside the users viewport. Thats why i normally have to do something like this:
//client
Posts.find({locs: {$geoWithin: {$box:
[[bottom_left_x, bottom_left_y],
[upper_right_x, upper_right_y]]}}},
{sort: {submitted: -1}, limit: limit}).observeChanges({
But thats not possible. GeoWithin is not supported inside minimongo and it is not possible to call oberserve with a collection that has a limit.
Has anyone an idea how to accomplish this?
Maybe there is a way to push the posts i get from subcription directly to the map without using a query on minimongo?

Answer 1

The solution is so easy !
Meteor.autosubscribe( function () {
Meteor.subscribe( 'chat', { room: Session.get( 'currentRoom' ) } );
} );
If you want to limit your subscription to the maps viewport with changing viewport-bounds, than you have to use autosubscribe. It seems that autosubscribe takes care of changing subscription-arguments :)
Meteor.autosubscribe( function () {
var a = Session.get('bounds');
if(a)
Meteor.subscribe( 'posts', a.swlat, a.swlng, a.nelat, a.nelng, 5 );
} );