Moving data between pixel and lat/lng domain

mercator.rb

module Projection
  MAP_WIDTH = [128, 256, 512, 1024, 2048, 4096, 8192, 16384, 32768, 65536, 131072, 262144, 524288, 1048576, 2097152, 4194304, 8388608, 16777216, 33554432, 67108864, 134217728, 268435456, 536870912, 1073741824, 2147483648, 4294967296, 8589934592, 17179869184, 34359738368, 68719476736, 137438953472]
  LNG_SCALE_AT_ZOOM = [0.7111111111111111, 1.4222222222222223, 2.8444444444444446, 5.688888888888889, 11.377777777777778, 22.755555555555556, 45.51111111111111, 91.02222222222223, 182.04444444444445, 364.0888888888889, 728.1777777777778, 1456.3555555555556, 2912.711111111111, 5825.422222222222, 11650.844444444445, 23301.68888888889, 46603.37777777778, 93206.75555555556, 186413.51111111112, 372827.02222222224, 745654.0444444445, 1491308.088888889, 2982616.177777778, 5965232.355555556, 11930464.711111112, 23860929.422222223, 47721858.844444446, 95443717.68888889, 190887435.37777779, 381774870.75555557, 763549741.5111111]
  LAT_SCALE_AT_ZOOM = [40.74366543152521, 81.48733086305042, 162.97466172610083, 325.94932345220167, 651.8986469044033, 1303.7972938088067, 2607.5945876176133, 5215.189175235227, 10430.378350470453, 20860.756700940907, 41721.51340188181, 83443.02680376363, 166886.05360752725, 333772.1072150545, 667544.214430109, 1335088.428860218, 2670176.857720436, 5340353.715440872, 10680707.430881744, 21361414.86176349, 42722829.72352698, 85445659.44705395, 170891318.8941079, 341782637.7882158, 683565275.5764316, 1367130551.1528633, 2734261102.3057265, 5468522204.611453, 10937044409.222906, 21874088818.445812, 43748177636.891624]
end

class MercatorProjection
  include Projection

  def latlng_to_pixel(lat,lng,zoom)
    current_width = MAP_WIDTH[zoom]
  
    x = current_width + (lng * LNG_SCALE_AT_ZOOM[zoom])
  
    tmp = Math.sin(lat * Math::PI / 180.0)
  
    # This prevents coordinates wrapping around the map
    if tmp < -0.9999
      tmp = -0.9999
    elsif tmp > 0.9999
      tmp = 0.9999
    end  
  
    y = current_width + (0.5 * Math.log( (1.0+tmp) / (1.0-tmp)) * -LAT_SCALE_AT_ZOOM[zoom] )
    
    [x.round,y.round]
  end

  def pixel_to_latlng(x,y,zoom)
    current_width = MAP_WIDTH[zoom]
  
    lng = (x - current_width) / LNG_SCALE_AT_ZOOM[zoom]
    tmp_lat = (y - current_width) / -LAT_SCALE_AT_ZOOM[zoom]
    trans = 2 * Math.atan(Math.exp(tmp_lat)) - Math::PI / 2
    lat = trans / (Math::PI / 180.0)
    
    [lat,lng]
  end
end