require File.dirname(__FILE__) + '/../test_helper'
class ShortLinkTest < ActiveSupport::TestCase
##
# tests that encoding and decoding are working to within
# the acceptable quantisation range.
def test_encode_decode
cases = Array.new
1000.times do
cases << [ 180.0 * rand - 90.0, 360.0 * rand - 180.0, (18 * rand).to_i ]
end
cases.each do |lat, lon, zoom|
lon2, lat2, zoom2 = ShortLink.decode(ShortLink.encode(lon, lat, zoom))
# zooms should be identical
assert_equal zoom, zoom2, "Decoding a encoded short link gives different zoom for (#{lat}, #{lon}, #{zoom})."
# but the location has a quantisation error introduced at roughly
# one pixel (i.e: zoom + 8). the sqrt(5) is because each position
# has an extra bit of accuracy in the lat coordinate, due to the
# smaller range.
distance = Math.sqrt((lat - lat2) ** 2 + (lon - lon2) ** 2)
max_distance = 360.0 / (1 << (zoom + 8)) * 0.5 * Math.sqrt(5)
assert max_distance > distance, "Maximum expected error exceeded: #{max_distance} <= #{distance} for (#{lat}, #{lon}, #{zoom})."
end
end
end