spherical.rb in graticule-0.1.2

- old
+ new

@@ -1,15 +1,22 @@
 module Graticule
   module Distance
 
     #
-    # Distance Measured usign the Spherical Law of Cosines
-    # Simplist though least accurate (earth isn't a perfect sphere)
-    # d = acos(sin(lat1).sin(lat2)+cos(lat1).cos(lat2).cos(long2−long1)).R
+    # The Spherical Law of Cosines is the simplist though least accurate distance
+    # formula (earth isn't a perfect sphere).
     #
     class Spherical < DistanceFormula
 
+      # Calculate the distance between two Locations using the Spherical formula
+      #
+      #   Graticule::Distance::Spherical.distance(
+      #     Graticule::Location.new(:latitude => 42.7654, :longitude => -86.1085),
+      #     Graticule::Location.new(:latitude => 41.849838, :longitude => -87.648193)
+      #   )
+      #   #=> 101.061720831853
+      #
       def self.distance(from, to, units = :miles)
         from_longitude   = deg2rad(from.longitude)
         from_latitude    = deg2rad(from.latitude)
         to_longitude  = deg2rad(to.longitude)
         to_latitude   = deg2rad(to.latitude)
@@ -22,9 +29,24 @@
             Math.cos(to_latitude) *
             Math.cos(to_longitude - from_longitude)
         ) * EARTH_RADIUS[units.to_sym]
       end
 
+      def self.to_sql(options)
+        options = {
+          :units => :miles,
+          :latitude_column => 'latitude',
+          :longitude_column => 'longitude'
+        }.merge(options)
+        %{(ACOS(
+            SIN(RADIANS(#{options[:latitude]})) *
+            SIN(RADIANS(#{options[:latitude_column]})) +
+            COS(RADIANS(#{options[:latitude]})) *
+            COS(RADIANS(#{options[:latitude_column]})) *
+            COS(RADIANS(#{options[:longitude_column]}) - RADIANS(#{options[:longitude]}))
+          ) * #{Graticule::Distance::EARTH_RADIUS[options[:units].to_sym]})
+        }.gsub("\n", '').squeeze(" ")
+      end
   
     end
   end
 end
\ No newline at end of file