Simple example code for geo-based chatting.

GeoChatClient

$(function(){
    ws = new WebSocket("ws://localhost:8080");

    ws.onmessage = function(evt) {
        if ($('#chat tbody tr:first').length > 0){
            $('#chat tbody tr:first').before('<tr><td>' + evt.data + '</td></tr>');  
        } else {
            $('#chat tbody').append('<tr><td>' + evt.data + '</td></tr>');  
        }
    };

    ws.onclose = function() { 
    };

    ws.onopen = function() {
        navigator.geolocation.getCurrentPosition( function (pos) {
            var msg = { text: "Joins the chat!",
                locus: [pos.coords.latitude, pos.coords.longitude] };
            ws.send( JSON.stringify(msg));
        });
    };


    $("form").submit(function(e) {
        if($("#msg").val().length > 0) {
            var theMessage = $("#msg").val();
            navigator.geolocation.getCurrentPosition( function (pos) {
                var msg = { text: theMessage,
                    locus: [pos.coords.latitude, pos.coords.longitude] };
                ws.send( JSON.stringify(msg));
            });
            $("#msg").val("");
        }
        return false;
    });

    $("#clear").click( function() {
        $('#chat tbody tr').remove();
    });

});

GeoChatServer

#thanks https://github.com/amscotti/em_sinatra_chat

require 'rubygems'
require 'em-websocket'
require 'yajl'
require 'haml'
require 'sinatra/base'
require 'thin'
require 'json'

$channel = EM::Channel.new

#thanks http://codingandweb.blogspot.com/2012/04/calculating-distance-between-two-points.html
# distance is in miles
def distance_between_lat_long_pairs( a, b )

    dtor = Math::PI/180
    r = 3959

    rlat1 = a[0] * dtor
    rlong1 = a[1] * dtor
    rlat2 = b[0] * dtor
    rlong2 = b[1] * dtor

    dlon = rlong1 - rlong2
    dlat = rlat1 - rlat2

    a = (Math::sin(dlat/2)**2) + Math::cos(rlat1) * Math::cos(rlat2) * (Math::sin(dlon/2)**2)
    c = 2 * Math::atan2(Math::sqrt(a), Math::sqrt(1-a))
    d = r * c

    return d
end

# hash mapping websockets to latlong pairs.
openConnections = {}

EventMachine.run do
    class App < Sinatra::Base
        get '/' do
            haml :index
        end
    end

    EventMachine::WebSocket.start(:host => '0.0.0.0', :port => 8080) do |ws|
        ws.onopen {
                    openConnections.each do | k,locus|
                        k.send("Hello #{ws.object_id}!")
                    end

            ws.onmessage { |msg|
                    message = JSON.parse(msg)                    

                    # add ourselves to the hash
                    openConnections[ws] = message["locus"]
                    origin = message["locus"]

                    # message everyone else within a mile radius
                    openConnections.each do | k, dest|
                        distance = distance_between_lat_long_pairs( origin, dest)
                        k.send("#{ws.object_id}: #{message["text"]}") unless distance > 1
                    end
            }

            ws.onclose {
                    openConnections.each do | k,locus|
                        k.send("Goodbye #{ws.object_id}!")
                    end
            }
        }

    end

    App.run!({:port => 3000})
end