Dynamically load Google Maps Markers with gmaps4ra

How do I load only markers that are inside the map bounds with gmaps4rails? And of course load new ones after pan and/or zoom.

Directly related to that, how can I get the current boundaries and zoomlevel of the map?

回答1:

Here is how I did it, I only replace the markers after the user finishes panning or zooming, if you require different behavior then use a different event listener:

In your view (index.html.erb):

<%= gmaps({ "map_options" => { "zoom" => 15, 
                               "auto_adjust" => false, 
                               "detect_location" => true, 
                               "center_on_user" => true }}, false, true) %>

At the bottom of your view add:

<script type="text/javascript" charset="utf-8">

function gmaps4rails_callback() {
    google.maps.event.addListener(Gmaps4Rails.map, 'idle', function () {
        var bounds = Gmaps4Rails.map.getBounds();
        drawItems(bounds);
    });
}

</script>

In application.js (using jQuery):

function drawItems(theBounds) {
    var url = '/venues.json/?sw_y=' + theBounds.getSouthWest().lng() + 
                           '&sw_x=' + theBounds.getSouthWest().lat() + 
                           '&ne_y=' + theBounds.getNorthEast().lng() +
                           '&ne_x=' + theBounds.getNorthEast().lat();
    $.get(url, function(newItemData) {
        Gmaps4Rails.replace_markers(newItemData);
    });
}

venues_controller#index:

def index
    # Only pull venues within the visible bounds of the map
    if (params[:sw_y] && params[:sw_x] && params[:ne_y] && params[:ne_x])
        bounds = [ [params[:sw_x].to_f, params[:sw_y].to_f], 
                 [params[:ne_x].to_f, params[:ne_y].to_f] ]
        @venues_within_bounds = Venue.within_bounds(bounds)
    else
        @venues_within_bounds = Venue.all
    end   

    respond_to do |format|
        format.html # index.html.erb
        format.json { 
            @data = @venues_within_bounds.collect {|v| {
                     :longitude => v.longitude, 
                     :latitude => v.latitude, 
                     :picture => v.marker_picture, 
                     :title => v.marker_title 
            }
            render :json => @data
        }
    end
end

Venue.rb model (using mongodb and mongoid):

def self.within_bounds(bounds)
    self.where(:location.within => {"$box" => bounds })
end

回答2:

Wow, you really provide much feedback for the gem :)

Here is how I use it:

to load only the useful markers, I filter them using geokit-rails3 and the following scope: Location.in_bounds([@south_west_point, @north_east_point], :origin => @somewhere)
when zoom or span, I only rely on the clustering which fasten the process
to configure, map center and original zoom, see here
you should code yourself the method to get the current boundaries, consider pulling :)