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Contents
# encoding: UTF-8
module Graticule
module Distance
#
# 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 = from.longitude.to_radians
from_latitude = from.latitude.to_radians
to_longitude = to.longitude.to_radians
to_latitude = to.latitude.to_radians
Math.acos(
Math.sin(from_latitude) *
Math.sin(to_latitude) +
Math.cos(from_latitude) *
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(LEAST(1,
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
Version data entries
7 entries across 7 versions & 1 rubygems