Fix a typo, clean up code, use full references to Math module methods.

lib/geocoder.rb

@@ -215,28 +215,28 @@ module Geocoder
   
   ##
   # Compute the geographic center (aka geographic midpoint, center of
-  # gravity) for an array of [lat,lon] points.
+  # gravity) for an array of [lat,lon] points. Follows the procedure
+  # documented at http://www.geomidpoint.com/calculation.html.
   #
   def self.geographic_center(points)
     
     # convert to Cartesian coordinates
-    x = []; y = [], z = []
+    x = []; y = []; z = []
     points.each do |p|
-      x << cos(p[0]) * cos(p[1])
-      y << cos(p[0]) * sin(p[1])
-      z << sin(p[0])
+      x << Math.cos(p[0]) * Math.cos(p[1])
+      y << Math.cos(p[0]) * Math.sin(p[1])
+      z << Math.sin(p[0])
     end
-    
-    # compute average coordinates
-    avg = [x,y,z].map do |c|
-      c.inject(0){ |tot,i| tot += i }
+
+    # compute average coordinate values
+    xa, ya, za = [x,y,z].map do |c|
+      c.inject(0){ |tot,i| tot += i } / c.size.to_f
     end
     
     # convert back to latitude/longitude
-    xa, ya, za = avg
-    lon = atan2(ya, xa)
-    hyp = sqrt(xa * xa + ya * ya)
-    lat = atan2(za, hyp)
+    lon = Math.atan2(ya, xa)
+    hyp = Math.sqrt(xa * xa + ya * ya)
+    lat = Math.atan2(za, hyp)
     
     [lat,lon]
   end

test/geocoder_test.rb

@@ -15,6 +15,9 @@ class GeocoderTest < Test::Unit::TestCase
   
   # sanity check
   def test_geographic_center
-    assert_equal 69, Geocoder.geographic_center([[0,0], [0,1]]).round
+    assert_equal [0.0, 0.5],
+      Geocoder.geographic_center([[0,0], [0,1]])
+    assert_equal [0.0, 1.0],
+      Geocoder.geographic_center([[0,0], [0,1], [0,2]])
   end
 end