# Each character encodes 3 bits of x and 3 of y, so there are extra characters
# tacked on the end to make the zoom levels "work".
module ShortLink
-
# array of 64 chars to encode 6 bits. this is almost like base64 encoding, but
# the symbolic chars are different, as base64's + and / aren't very
# URL-friendly.
- ARRAY = ('A'..'Z').to_a + ('a'..'z').to_a + ('0'..'9').to_a + ['_','~']
+ ARRAY = ("A".."Z").to_a + ("a".."z").to_a + ("0".."9").to_a + ["_", "~"]
+
+ class << self
+ ##
+ # Given a string encoding a location, returns the [lon, lat, z] tuple of that
+ # location.
+ def decode(str)
+ x = 0
+ y = 0
+ z = 0
+ z_offset = 0
- ##
- # Given a string encoding a location, returns the [lon, lat, z] tuple of that
- # location.
- def self.decode(str)
- x = 0
- y = 0
- z = 0
- z_offset = 0
+ # keep support for old shortlinks which use the @ character, now
+ # replaced by the ~ character because twitter is horribly broken
+ # and we can't have that.
+ str.tr!("@", "~")
- # keep support for old shortlinks which use the @ character, now
- # replaced by the ~ character because twitter is horribly broken
- # and we can't have that.
- str.gsub!("@","~")
+ str.each_char do |c|
+ t = ARRAY.index c
+ if t.nil?
+ z_offset -= 1
+ else
+ 3.times do
+ x <<= 1
+ x |= 1 unless t.nobits?(32)
+ t <<= 1
- str.each_char do |c|
- t = ARRAY.index c
- if t.nil?
- z_offset -= 1
- else
- 3.times do
- x <<= 1; x = x | 1 unless (t & 32).zero?; t <<= 1
- y <<= 1; y = y | 1 unless (t & 32).zero?; t <<= 1
+ y <<= 1
+ y |= 1 unless t.nobits?(32)
+ t <<= 1
+ end
+ z += 3
end
- z += 3
end
+ # pack the coordinates out to their original 32 bits.
+ x <<= (32 - z)
+ y <<= (32 - z)
+
+ # project the parameters back to their coordinate ranges.
+ [(x * 360.0 / (2**32)) - 180.0,
+ (y * 180.0 / (2**32)) - 90.0,
+ z - 8 - (z_offset % 3)]
end
- # pack the coordinates out to their original 32 bits.
- x <<= (32 - z)
- y <<= (32 - z)
- # project the parameters back to their coordinate ranges.
- [(x * 360.0 / 2**32) - 180.0,
- (y * 180.0 / 2**32) - 90.0,
- z - 8 - (z_offset % 3)]
- end
+ ##
+ # given a location and zoom, return a short string representing it.
+ def encode(lon, lat, z)
+ code = interleave_bits(((lon + 180.0) * (2**32) / 360.0).to_i,
+ ((lat + 90.0) * (2**32) / 180.0).to_i)
+ str = ""
+ # add eight to the zoom level, which approximates an accuracy of
+ # one pixel in a tile.
+ ((z + 8) / 3.0).ceil.times do |i|
+ digit = (code >> (58 - (6 * i))) & 0x3f
+ str << ARRAY[digit]
+ end
+ # append characters onto the end of the string to represent
+ # partial zoom levels (characters themselves have a granularity
+ # of 3 zoom levels).
+ ((z + 8) % 3).times { str << "-" }
- ##
- # given a location and zoom, return a short string representing it.
- def self.encode(lon, lat, z)
- code = interleave_bits(((lon + 180.0) * 2**32 / 360.0).to_i,
- ((lat + 90.0) * 2**32 / 180.0).to_i)
- str = ""
- # add eight to the zoom level, which approximates an accuracy of
- # one pixel in a tile.
- ((z + 8)/3.0).ceil.times do |i|
- digit = (code >> (58 - 6 * i)) & 0x3f
- str << ARRAY[digit]
+ str
end
- # append characters onto the end of the string to represent
- # partial zoom levels (characters themselves have a granularity
- # of 3 zoom levels).
- ((z + 8) % 3).times { str << "-" }
- return str
- end
-
- private
+ private
- ##
- # interleaves the bits of two 32-bit numbers. the result is known
- # as a Morton code.
- def self.interleave_bits(x, y)
- c = 0
- 31.downto(0) do |i|
- c = (c << 1) | ((x >> i) & 1)
- c = (c << 1) | ((y >> i) & 1)
+ ##
+ # interleaves the bits of two 32-bit numbers. the result is known
+ # as a Morton code.
+ def interleave_bits(x, y)
+ c = 0
+ 31.downto(0) do |i|
+ c = (c << 1) | ((x >> i) & 1)
+ c = (c << 1) | ((y >> i) & 1)
+ end
+ c
end
- c
end
-
end
projects / rails.git / blobdiff