Merge pull request #2 from geocrystal/adjust-earth-radius

set Earth radius to 6371008.8

spec/haversine_spec.cr

@@ -13,9 +13,9 @@ describe Haversine do
     end
 
     describe "calculates the distance between the provided lat/lon pairs" do
-      it { Haversine.distance(0, 0, 0, 0).great_circle_distance.should eq(0) }
-      it { Haversine.distance([0.0, 0.0], [0.0, 0.0]).great_circle_distance.should eq(0) }
-      it { Haversine.distance({0.0, 0.0}, {0.0, 0.0}).great_circle_distance.should eq(0) }
+      it { Haversine.distance(0, 0, 0, 0).distance.should eq(0) }
+      it { Haversine.distance([0.0, 0.0], [0.0, 0.0]).distance.should eq(0) }
+      it { Haversine.distance({0.0, 0.0}, {0.0, 0.0}).distance.should eq(0) }
     end
 
     describe "computes distances correctly" do
@@ -24,11 +24,11 @@ describe Haversine do
 
       dist = Haversine.distance(new_york, london)
 
-      it { dist.to_kilometers.should eq(5570.4744596620685) }
-      it { dist.to_meters.should eq(5570474.459662069) }
-      it { dist.to_miles.should eq(3458.9227691764468) }
-      it { dist.to_nautical_miles.should eq(3005.720267276497) }
-      it { dist.to_feet.should eq(18263112.22125164) }
+      it { dist.to_kilometers.should eq(5570.482153929098) }
+      it { dist.to_meters.should eq(5570482.153929098) }
+      it { dist.to_miles.should eq(3461.3371373237155) }
+      it { dist.to_nautical_miles.should eq(3007.8197375427094) }
+      it { dist.to_feet.should eq(18275860.669896744) }
     end
   end
 end

src/haversine/distance.cr

@@ -2,39 +2,29 @@ module Haversine
   class Distance
     include Comparable(self)
 
-    GREAT_CIRCLE_RADIUS_KILOMETERS     = 6371
-    GREAT_CIRCLE_RADIUS_METERS         = GREAT_CIRCLE_RADIUS_KILOMETERS * 1000
-    GREAT_CIRCLE_RADIUS_MILES          = 3956
-    GREAT_CIRCLE_RADIUS_FEET           = GREAT_CIRCLE_RADIUS_MILES * 5280
-    GREAT_CIRCLE_RADIUS_NAUTICAL_MILES = GREAT_CIRCLE_RADIUS_MILES / 1.15078
+    EARTH_RADIUS = 6371008.8
 
-    property great_circle_distance
+    FACTORS = {
+      kilometers:     EARTH_RADIUS / 1000,
+      meters:         EARTH_RADIUS,
+      miles:          EARTH_RADIUS / 1609.344,
+      feet:           EARTH_RADIUS * 3.28084,
+      nautical_miles: EARTH_RADIUS / 1852,
+    }
 
-    def initialize(@great_circle_distance : Number)
-    end
-
-    def to_kilometers : Number
-      @great_circle_distance * GREAT_CIRCLE_RADIUS_KILOMETERS
-    end
-
-    def to_meters : Number
-      @great_circle_distance * GREAT_CIRCLE_RADIUS_METERS
-    end
-
-    def to_miles : Number
-      @great_circle_distance * GREAT_CIRCLE_RADIUS_MILES
-    end
+    property distance
 
-    def to_nautical_miles : Number
-      @great_circle_distance * GREAT_CIRCLE_RADIUS_NAUTICAL_MILES
+    def initialize(@distance : Number)
     end
 
-    def to_feet : Number
-      @great_circle_distance * GREAT_CIRCLE_RADIUS_FEET
-    end
+    {% for factor in ["meters", "kilometers", "miles", "nautical_miles", "feet"] %}
+      def to_{{factor.id}} : Number
+        @distance * FACTORS[:{{factor.id}}]
+      end
+    {% end %}
 
     def <=>(other : Haversine::Distance)
-      great_circle_distance <=> other.great_circle_distance
+      distance <=> other.distance
     end
   end
 end