From fbca35bcff9bd1815cee011347d108c8355ac7f0 Mon Sep 17 00:00:00 2001
From: Alex Reisner <alex@alexreisner.com>
Date: Fri, 21 Jan 2011 16:11:42 -0500
Subject: [PATCH] Create Geocoder::Calculations module.
Move some methods into it (organize!).
---
README.rdoc | 8 +--
lib/geocoder.rb | 101 +++--------------------------------
lib/geocoder/calculations.rb | 94 ++++++++++++++++++++++++++++++++
test/geocoder_test.rb | 6 +--
4 files changed, 109 insertions(+), 100 deletions(-)
create mode 100644 lib/geocoder/calculations.rb
diff --git a/README.rdoc b/README.rdoc
index 9b9995d4..fcfde062 100644
--- a/README.rdoc
+++ b/README.rdoc
@@ -68,13 +68,13 @@ To find objects by location, use the following scopes:
Some utility methods are also available:
# distance (in miles) between Eiffel Tower and Empire State Building
- Geocoder.distance_between( 48.858205,2.294359, 40.748433,-73.985655 )
+ Geocoder::Calculations.distance_between( 48.858205,2.294359, 40.748433,-73.985655 )
# look up coordinates of some location (like searching Google Maps)
Geocoder.fetch_coordinates("25 Main St, Cooperstown, NY")
# find the geographic center (aka center of gravity) of objects or points
- Geocoder.geographic_center([ city1, city2, city3, [40.22,-73.99], city4 ])
+ Geocoder::Calculations.geographic_center([ city1, city2, city3, [40.22,-73.99], city4 ])
== More On Configuration
@@ -114,9 +114,9 @@ There are few options for finding objects near a given point in SQLite without i
1. Use a square instead of a circle for finding nearby points. For example, if you want to find points near 40.71, 100.23, search for objects with latitude between 39.71 and 41.71 and longitude between 99.23 and 101.23. One degree of latitude or longitude is at most 69 miles so divide your radius (in miles) by 69.0 to get the amount to add and subtract from your center coordinates to get the upper and lower bounds. The results will not be very accurate (you'll get points outside the desired radius--at worst 29% farther away), but you will get all the points within the required radius.
-2. Load all objects into memory and compute distances between them using the <tt>Geocoder.distance_between</tt> method. This will produce accurate results but will be very slow (and use a lot of memory) if you have a lot of objects in your database.
+2. Load all objects into memory and compute distances between them using the <tt>Geocoder::Calculations.distance_between</tt> method. This will produce accurate results but will be very slow (and use a lot of memory) if you have a lot of objects in your database.
-3. If you have a large number of objects (so you can't use approach #2) and you need accurate results (better than approach #1 will give), you can use a combination of the two. Get all the objects within a square around your center point, and then eliminate the ones that are too far away using <tt>Geocoder.distance_between</tt>.
+3. If you have a large number of objects (so you can't use approach #2) and you need accurate results (better than approach #1 will give), you can use a combination of the two. Get all the objects within a square around your center point, and then eliminate the ones that are too far away using <tt>Geocoder::Calculations.distance_between</tt>.
Because Geocoder needs to provide this functionality as a scope, we must go with option #1, but feel free to implement #2 or #3 if you need more accuracy.
diff --git a/lib/geocoder.rb b/lib/geocoder.rb
index f1a5099f..633c21d7 100644
--- a/lib/geocoder.rb
+++ b/lib/geocoder.rb
@@ -1,3 +1,5 @@
+require "geocoder/calculations"
+
##
# Add geocoding functionality (via Google) to any object.
#
@@ -55,7 +57,7 @@ module Geocoder
# +select+ :: string with the SELECT SQL fragment (e.g. “id, nameâ€)
#
def near_scope_options(latitude, longitude, radius = 20, options = {})
- radius *= km_in_mi if options[:units] == :km
+ radius *= Geocoder::Calculations.km_in_mi if options[:units] == :km
if ActiveRecord::Base.connection.adapter_name == "SQLite"
approx_near_scope_options(latitude, longitude, radius, options)
else
@@ -138,13 +140,6 @@ module Geocoder
longitude + (radius / factor)
]
end
-
- ##
- # Conversion factor: km to mi.
- #
- def km_in_mi
- 0.621371192
- end
end
##
@@ -164,17 +159,19 @@ module Geocoder
##
# Calculate the distance from the object to a point (lat,lon).
- # Valid units are defined in <tt>distance_between</tt> class method.
+ #
+ # <tt>:units</tt> :: <tt>:mi</tt> (default) or <tt>:km</tt>
#
def distance_to(lat, lon, units = :mi)
return nil unless geocoded?
mylat,mylon = read_coordinates
- Geocoder.distance_between(mylat, mylon, lat, lon, :units => units)
+ Geocoder::Calculations.distance_between(mylat, mylon, lat, lon, :units => units)
end
##
# Get other geocoded objects within a given radius.
- # Valid units are defined in <tt>distance_between</tt> class method.
+ #
+ # <tt>:units</tt> :: <tt>:mi</tt> (default) or <tt>:km</tt>
#
def nearbys(radius = 20, units = :mi)
return [] unless geocoded?
@@ -205,88 +202,6 @@ module Geocoder
fetch_coordinates(true)
end
- ##
- # Calculate the distance between two points on Earth (Haversine formula).
- # Takes two sets of coordinates and an options hash:
- #
- # <tt>:units</tt> :: <tt>:mi</tt> (default) or <tt>:km</tt>
- #
- def self.distance_between(lat1, lon1, lat2, lon2, options = {})
-
- # set default options
- options[:units] ||= :mi
-
- # define conversion factors
- conversions = { :mi => 3956, :km => 6371 }
-
- # convert degrees to radians
- lat1 = to_radians(lat1)
- lon1 = to_radians(lon1)
- lat2 = to_radians(lat2)
- lon2 = to_radians(lon2)
-
- # compute distances
- dlat = (lat1 - lat2).abs
- dlon = (lon1 - lon2).abs
-
- a = (Math.sin(dlat / 2))**2 + Math.cos(lat1) *
- (Math.sin(dlon / 2))**2 * Math.cos(lat2)
- c = 2 * Math.atan2( Math.sqrt(a), Math.sqrt(1-a))
- c * conversions[options[:units]]
- end
-
- ##
- # Compute the geographic center (aka geographic midpoint, center of
- # gravity) for an array of geocoded objects and/or [lat,lon] arrays
- # (can be mixed). Any objects missing coordinates are ignored. Follows
- # the procedure documented at http://www.geomidpoint.com/calculation.html.
- #
- def self.geographic_center(points)
-
- # convert objects to [lat,lon] arrays and remove nils
- points = points.map{ |p|
- p.is_a?(Array) ? p : (p.geocoded?? p.read_coordinates : nil)
- }.compact
-
- # convert degrees to radians
- points.map!{ |p| [to_radians(p[0]), to_radians(p[1])] }
-
- # convert to Cartesian coordinates
- x = []; y = []; z = []
- points.each do |p|
- 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 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
- lon = Math.atan2(ya, xa)
- hyp = Math.sqrt(xa**2 + ya**2)
- lat = Math.atan2(za, hyp)
-
- # return answer in degrees
- [to_degrees(lat), to_degrees(lon)]
- end
-
- ##
- # Convert degrees to radians.
- #
- def self.to_radians(degrees)
- degrees * (Math::PI / 180)
- end
-
- ##
- # Convert radians to degrees.
- #
- def self.to_degrees(radians)
- (radians * 180.0) / Math::PI
- end
-
##
# Query Google for geographic information about the given phrase.
# Returns a hash representing a valid geocoder response.
diff --git a/lib/geocoder/calculations.rb b/lib/geocoder/calculations.rb
new file mode 100644
index 00000000..1e71c787
--- /dev/null
+++ b/lib/geocoder/calculations.rb
@@ -0,0 +1,94 @@
+module Geocoder
+ module Calculations
+ extend self
+
+ ##
+ # Calculate the distance between two points on Earth (Haversine formula).
+ # Takes two sets of coordinates and an options hash:
+ #
+ # <tt>:units</tt> :: <tt>:mi</tt> (default) or <tt>:km</tt>
+ #
+ def distance_between(lat1, lon1, lat2, lon2, options = {})
+
+ # set default options
+ options[:units] ||= :mi
+
+ # define conversion factors
+ conversions = { :mi => 3956, :km => 6371 }
+
+ # convert degrees to radians
+ lat1 = to_radians(lat1)
+ lon1 = to_radians(lon1)
+ lat2 = to_radians(lat2)
+ lon2 = to_radians(lon2)
+
+ # compute distances
+ dlat = (lat1 - lat2).abs
+ dlon = (lon1 - lon2).abs
+
+ a = (Math.sin(dlat / 2))**2 + Math.cos(lat1) *
+ (Math.sin(dlon / 2))**2 * Math.cos(lat2)
+ c = 2 * Math.atan2( Math.sqrt(a), Math.sqrt(1-a))
+ c * conversions[options[:units]]
+ end
+
+ ##
+ # Compute the geographic center (aka geographic midpoint, center of
+ # gravity) for an array of geocoded objects and/or [lat,lon] arrays
+ # (can be mixed). Any objects missing coordinates are ignored. Follows
+ # the procedure documented at http://www.geomidpoint.com/calculation.html.
+ #
+ def geographic_center(points)
+
+ # convert objects to [lat,lon] arrays and remove nils
+ points = points.map{ |p|
+ p.is_a?(Array) ? p : (p.geocoded?? p.read_coordinates : nil)
+ }.compact
+
+ # convert degrees to radians
+ points.map!{ |p| [to_radians(p[0]), to_radians(p[1])] }
+
+ # convert to Cartesian coordinates
+ x = []; y = []; z = []
+ points.each do |p|
+ 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 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
+ lon = Math.atan2(ya, xa)
+ hyp = Math.sqrt(xa**2 + ya**2)
+ lat = Math.atan2(za, hyp)
+
+ # return answer in degrees
+ [to_degrees(lat), to_degrees(lon)]
+ end
+
+ ##
+ # Convert degrees to radians.
+ #
+ def to_radians(degrees)
+ degrees * (Math::PI / 180)
+ end
+
+ ##
+ # Convert radians to degrees.
+ #
+ def to_degrees(radians)
+ (radians * 180.0) / Math::PI
+ end
+
+ ##
+ # Conversion factor: km to mi.
+ #
+ def km_in_mi
+ 0.621371192
+ end
+ end
+end
diff --git a/test/geocoder_test.rb b/test/geocoder_test.rb
index 518c88d9..d8f78948 100644
--- a/test/geocoder_test.rb
+++ b/test/geocoder_test.rb
@@ -10,14 +10,14 @@ class GeocoderTest < Test::Unit::TestCase
# sanity check
def test_distance_between
- assert_equal 69, Geocoder.distance_between(0,0, 0,1).round
+ assert_equal 69, Geocoder::Calculations.distance_between(0,0, 0,1).round
end
# sanity check
def test_geographic_center
assert_equal [0.0, 0.5],
- Geocoder.geographic_center([[0,0], [0,1]])
+ Geocoder::Calculations.geographic_center([[0,0], [0,1]])
assert_equal [0.0, 1.0],
- Geocoder.geographic_center([[0,0], [0,1], [0,2]])
+ Geocoder::Calculations.geographic_center([[0,0], [0,1], [0,2]])
end
end
--
GitLab