Use raw sql to calculate distance between latitude/longitude coordinates

raw_sql_to_calculate_distance.rb

# Use raw sql to calculate distance between latitude/longitude coordinates

# From the web
# - http://gis.stackexchange.com/questions/31628/find-points-within-a-distance-using-mysql
"SELECT
  id, (
    3959 * acos (
      cos ( radians(78.3232) )
      * cos( radians( lat ) )
      * cos( radians( lng ) - radians(65.3234) )
      + sin ( radians(78.3232) )
      * sin( radians( lat ) )
    )
  ) AS distance
FROM markers
HAVING distance < 30
ORDER BY distance
LIMIT 0 , 20;"

# Example usage in ActiveRecord Model
# ActiveRecord::Base.connection.quote to prevent SQL injections
class Market < ActiveRecord::Base
  scope :nearest_to, lambda { |latitude, longitude|
    select("markets.*,
            (3963.19 * acos (
              cos ( radians( #{ActiveRecord::Base.connection.quote(latitude)} ) )
              * cos( radians( lat ) )
              * cos( radians( lng ) - radians( #{ActiveRecord::Base.connection.quote(longitude)} ) )
              + sin ( radians( #{ActiveRecord::Base.connection.quote(latitude)} ) )
              * sin( radians( lat ) )
              )) AS distance").
    order(:distance).having("distance < range_in_miles") }

  def find_market
    Market.nearest_to(latitude, longitude).first
  end
end

# Comparison of Raw SQL vs Geokit

# Raw SQL
[1] pry(#<Property>)> Market.with_distance(latitude, longitude).collect(&:distance).sort
=> [0.0,
 184.9088153239107,
 945.0517878990462,
 1099.1091011031144,
 1099.1091011031144,
 2231.5771018419705,
 2552.9080305439775,
 2569.7314203097667,
 8885.790207134487]

# GeoKit
[3] pry(#<Property>)> Market.by_distance(:origin => [latitude, longitude]).collect { |m| m.distance_to(self) }
=> [0.0,
 184.9088153239107,
 945.0517878990462,
 1099.1091011031126,
 1099.1091011031126,
 2231.5771018419714,
 2552.9080305439775,
 2569.7314203097667,
 8885.790207134487]

# Benchmarks
[2] pry(#<Property>)> Benchmark.measure{ Market.with_distance(latitude, longitude).collect(&:distance).sort }
=>   0.000000   0.000000   0.000000 (  0.001536)

[3] pry(#<Property>)> Benchmark.measure{ Market.by_distance(:origin => [latitude, longitude]).collect { |m| m.distance_to(self) } }
=>   0.000000   0.000000   0.000000 (  0.002511)