coordinate distance

gistfile1.txt

class StationLog < ActiveRecord::Base
  
  belongs_to :boat_log
  has_many :rep_logs, :dependent => :destroy
  accepts_nested_attributes_for :rep_logs, :reject_if => lambda {  |a| a[:replicate].blank? }, :allow_destroy => true


  

  def self.coorDist

    stn1_coordinates = [ self.where(stn_number: 1).first.latitude, self.where(stn_number: 1).first.longitude ]
    stn2_coordinates = [ self.where(stn_number: 2).first.latitude, self.where(stn_number: 2).first.longitude ]
    
    earthRadius = 6371000 # Earth's radius in meters

        # convert degrees to radians
        def self.convDegRad(value)
          unless value.nil? or value == 0
                value = (value/180) * Math::PI
          end
        return value
        end

    deltaLat = (stn2_coordinates[0] - stn1_coordinates[0])
    deltaLon = (stn2_coordinates[1] - stn1_coordinates[1])
    deltaLat = convDegRad(deltaLat)
    deltaLon = convDegRad(deltaLon)

    # Calculate square of half the chord length between latitude and longitude
    a = Math.sin(deltaLat/2) * Math.sin(deltaLat/2) +
        Math.cos((stn1_coordinates[0]/180 * Math::PI)) * Math.cos((stn2_coordinates[0]/180 * Math::PI)) *
        Math.sin(deltaLon/2) * Math.sin(deltaLon/2); 

    # Calculate the angular distance in radians
    c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a))

    distance = earthRadius * c

    return distance

  end
end


from console log...
irb(main):032:0> BoatLog.first.station_logs.coorDist
  BoatLog Load (0.4ms)  SELECT "boat_logs".* FROM "boat_logs" LIMIT 1
  StationLog Load (0.2ms)  SELECT "station_logs".* FROM "station_logs" WHERE "station_logs"."boat_log_id" = 4 AND "station_logs"."stn_number" = 1 LIMIT 1
  StationLog Load (0.3ms)  SELECT "station_logs".* FROM "station_logs" WHERE "station_logs"."boat_log_id" = 4 AND "station_logs"."stn_number" = 1 LIMIT 1
  StationLog Load (0.2ms)  SELECT "station_logs".* FROM "station_logs" WHERE "station_logs"."boat_log_id" = 4 AND "station_logs"."stn_number" = 2 LIMIT 1
  StationLog Load (0.2ms)  SELECT "station_logs".* FROM "station_logs" WHERE "station_logs"."boat_log_id" = 4 AND "station_logs"."stn_number" = 2 LIMIT 1
=> 3428.1395884519347