Ruby implementation of getBoundsZoomLevel JS

zoom_level.rb

def zoom_level_for_bounds(bounds, map_dim={ height: 1000, width: 1000 }, zoom_max=21)
  # See: http://stackoverflow.com/a/13274361/72

  return zoom_max if bounds.min_x == bounds.max_x and bounds.min_y == bounds.max_y

  world_dim = { height: 256, width: 256 }

  def lat_rad(lat)
    sin = Math.sin(lat * Math::PI / 180)
    rad_x2 = Math.log((1 + sin) / (1 - sin)) / 2
    [[rad_x2, Math::PI].min, -Math::PI].max / 2
  end

  def zoom(map_px, world_px, fraction)
    (Math.log(map_px / world_px / fraction) / Math.log(2)).floor
  end

  lat_fraction = (lat_rad(bounds.max_x) - lat_rad(bounds.min_x)).abs / Math::PI
  lng_diff = bounds.max_y - bounds.min_y
  lng_fraction = ((lng_diff < 0) ? (lng_diff + 360) : lng_diff) / 360

  lat_zoom = zoom(map_dim[:height], world_dim[:height], lat_fraction)
  lng_zoom = zoom(map_dim[:width], world_dim[:width], lng_fraction)

  return [lat_zoom, lng_zoom, zoom_max].min
end