distance_away_report.rb

MAX_DISTANCE_AWAY_IN_KM = 100.0
RAD_PER_DEG             = 0.017453293

Rmiles  = 3956           # radius of the great circle in miles
Rkm     = 6371           # radius in kilometers, some algorithms use 6367
Rfeet   = Rmiles * 5282  # radius in feet
Rmeters = Rkm * 1000     # radius in meters

def haversine_distance( lat1, lon1, lat2, lon2 )
  dlon = lon2 - lon1
  dlat = lat2 - lat1

  dlon_rad = dlon * RAD_PER_DEG
  dlat_rad = dlat * RAD_PER_DEG

  lat1_rad = lat1 * RAD_PER_DEG
  lon1_rad = lon1 * RAD_PER_DEG

  lat2_rad = lat2 * RAD_PER_DEG
  lon2_rad = lon2 * RAD_PER_DEG

  a = (Math.sin(dlat_rad/2))**2 + Math.cos(lat1_rad) *
       Math.cos(lat2_rad) * (Math.sin(dlon_rad/2))**2
  c = 2 * Math.atan2( Math.sqrt(a), Math.sqrt(1-a))

  dMi     = nil #Rmiles * c      # delta between the two points in miles
  dKm     = Rkm * c         # delta in kilometers
  dFeet   = nil #Rfeet * c       # delta in feet
  dMeters = nil #Rmeters * c     # delta in meters

  { :mi => dMi, :km => dKm, :ft => dFeet, :m => dMeters }
end

property_count, too_far_away_count = 0, 0

Property.find(:all, :conditions => ['location_id IS NOT NULL AND latitude IS NOT NULL AND longitude IS NOT NULL'], :joins => :location).each do |p|
  distance = haversine_distance(p.latitude, p.longitude, p.location.lat, p.location.lng)
  if distance[:km] > MAX_DISTANCE_AWAY_IN_KM
    puts "#{distance[:km].to_i} - Property:#{p.id} is #{distance[:km]} (km) from Location:#{p.location_id}"
    too_far_away_count += 1
  end
  property_count += 1
end

puts "Summary, #{property_count} scanned, #{too_far_away_count} deemed too far away (more than #{MAX_DISTANCE_AWAY_IN_KM})"