grid_clusterer.rb

grid_clusterer.rb

module GeoKit
  #It is half of the earth circumference in pixels at zoom level 21. 
  #You can visualize it by thinking of full map. Full map size is 536870912 × 536870912 pixels. 
  #Center of the map in pixel coordinates is 268435456,268435456 which in latitude and longitude would be 0,0.
  PIXEL_OFFSET = 268435456
  PIXEL_RADIUS = PIXEL_OFFSET / Math::PI
  
  module Mappable  
      
    module ClassMethods     
      def pixel_distance(from, to, zoom)        
        Math.sqrt((from[:x]-to[:x])**2 + (from[:y]-to[:y])**2).to_i >> (21-zoom)
      end
                             
      def cluster(markers, grid_size, zoom)
        # Scale grid-size based upon zoom
        distance = grid_size - (grid_size/ 21 * zoom / 1.5)
        
        # Once markers' pixel-distance become 4*grid_size, break from the each loop.
        threshold = grid_size * 4        
        clusters = []    		
        while(markers.count > 0) do          
          marker = markers.shift          
          cluster = []                    
          markers.each_index do |i|                      
            pd = pixel_distance(marker, markers[i], zoom)
            if distance > pd              
              cluster << markers.slice!(i)           
            elsif pd > threshold
              break
            end            
          end
          
          if cluster.length > 0
            count = 0
            len = 0
            avg_lat = 0
            avg_lng = 0
            cluster.each do |i|
              len += 1
              avg_lat += i[:lat]
              avg_lng += i[:lng]
              count += i[:count]
            end            
            cluster.sort {|i|
              i[:count]
            }   
            last = cluster.last
            clusters << ["cluster:#{last[:id].to_s}", avg_lat/len, avg_lng/len, count]
          else
            clusters << [marker[:id], marker[:lat], marker[:lng], marker[:count]]
          end
        end
        clusters
      end                    
    end
  end
end