From 2b7e5411733f8878809018a794db829548f43b84 Mon Sep 17 00:00:00 2001
From: Alex Reisner <alex@alexreisner.com>
Date: Thu, 24 Mar 2011 20:00:29 -0400
Subject: [PATCH] Add calculations for distances btwn lat/lon lines.
---
lib/geocoder/calculations.rb | 15 +++++++++++++++
test/geocoder_test.rb | 12 ++++++++++++
2 files changed, 27 insertions(+)
diff --git a/lib/geocoder/calculations.rb b/lib/geocoder/calculations.rb
index d9333d80..bc97d3b8 100644
--- a/lib/geocoder/calculations.rb
+++ b/lib/geocoder/calculations.rb
@@ -21,6 +21,21 @@ module Geocoder
#
KM_IN_MI = 0.621371192
+ ##
+ # Calculate the distance between latitude lines in the given units.
+ #
+ def distance_between_latitude_lines(units = :mi)
+ 2 * Math::PI * earth_radius(units) / 360
+ end
+
+ ##
+ # Calculate the distance between longitude lines at the given latitude.
+ # This ranges from around 69 miles at the equator to zero at the poles.
+ #
+ def distance_between_longitude_lines(latitude, units = :mi)
+ distance_between_latitude_lines(units) * Math.cos(to_radians(latitude))
+ end
+
##
# Calculate the distance between two points on Earth (Haversine formula).
# Takes two sets of coordinates and an options hash:
diff --git a/test/geocoder_test.rb b/test/geocoder_test.rb
index 5443e64a..91179e41 100644
--- a/test/geocoder_test.rb
+++ b/test/geocoder_test.rb
@@ -139,6 +139,18 @@ class GeocoderTest < Test::Unit::TestCase
# --- calcluations ---
+ def test_distance_between_longitude_lines_at_equator
+ assert_equal 69, Geocoder::Calculations.distance_between_longitude_lines(0).round
+ end
+
+ def test_distance_between_longitude_lines_at_new_york
+ assert_equal 53, Geocoder::Calculations.distance_between_longitude_lines(40).round
+ end
+
+ def test_distance_between_longitude_lines_at_north_pole
+ assert_equal 0, Geocoder::Calculations.distance_between_longitude_lines(89.98).round
+ end
+
def test_distance_between
assert_equal 69, Geocoder::Calculations.distance_between(0,0, 0,1).round
la_to_ny = Geocoder::Calculations.distance_between(34.05,-118.25, 40.72,-74).round
--
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