class SimpleMercatorLocation

Attributes

lat_deg[RW]

lon_deg[RW]

zoom[RW]

Public Class Methods

new(*args) click to toggle source

# File lib/simple_mercator_location.rb, line 5
def initialize(*args)
    @zoom = 2
    @lat_deg = 0
    @lon_deg = 0

    if args.first.is_a?(Hash)
        @lat_deg = args.first[:lat] if args.first.has_key?(:lat)
        @lon_deg = args.first[:lon] if args.first.has_key?(:lon)
        @zoom = args.first[:zoom] if args.first.has_key?(:zoom)
    end
end

Public Instance Methods

earth_radius() click to toggle source

earth radius in meters

# File lib/simple_mercator_location.rb, line 49
def earth_radius 
  6378137
end

lat_rad() click to toggle source

latitude in radiants

# File lib/simple_mercator_location.rb, line 19
def lat_rad
  shift_to_rad * lat_deg
end

lat_scaled_deg() click to toggle source

returns the scaled latitude as degrees

# File lib/simple_mercator_location.rb, line 91
def lat_scaled_deg
  lat_scaled_rad * shift_to_deg
end

lat_scaled_rad() click to toggle source

scale the latitude via mercator projections see en.wikipedia.org/wiki/Mercator_projection#Derivation_of_the_Mercator_projection return the scaled latitude as radiant

# File lib/simple_mercator_location.rb, line 85
def lat_scaled_rad
  Math.log( Math.tan( Rational(Math::PI,4) + Rational(lat_rad,2) )) 
end

lon_rad() click to toggle source

longitude in radiants

# File lib/simple_mercator_location.rb, line 25
def lon_rad
  shift_to_rad * lon_deg
end

origin_px() click to toggle source

origin of google map lieves on top-left. For getting pixels, we assume displaying the earh an zoomm-level 0 and a square tile of tile_size * tile_size pixels. The origin of our wsg84 system (lat, lon = (0,0) sits and (128,128)px.

# File lib/simple_mercator_location.rb, line 65
def origin_px
  [tile_size / 2, tile_size / 2]
end

pixel_per_degree() click to toggle source

return the pixels per degree

# File lib/simple_mercator_location.rb, line 71
def pixel_per_degree
  Rational(tile_size, 360)
end

pixel_per_rad() click to toggle source

return the pixels per radiant

# File lib/simple_mercator_location.rb, line 77
def pixel_per_rad
  tile_size / (2 * Math::PI) # tile_size / (360 * shift_to_rad)
end

shift_to_deg() click to toggle source

factor for scaling to degrees

# File lib/simple_mercator_location.rb, line 37
def shift_to_deg
  Rational(180.0, Math::PI)
end

shift_to_rad() click to toggle source

factor for scaling to radiants

# File lib/simple_mercator_location.rb, line 31
def shift_to_rad
  Rational(Math::PI, 180)
end

tile_size() click to toggle source

size of our tiles

# File lib/simple_mercator_location.rb, line 43
def tile_size
  256
end

to_m() click to toggle source

returns the mercotors meters count for the location

# File lib/simple_mercator_location.rb, line 97
def to_m
    mx = earth_radius * lon_rad
    my = earth_radius * lat_scaled_rad

    my = (my.round(8) == 0)? 0 : my

    [mx.to_f, my.to_f]
end

to_px() click to toggle source

returns the pixel coordinates at the given zoom level

# File lib/simple_mercator_location.rb, line 118
def to_px
  tiles_count = 2**zoom
  wx,wy = self.to_w
  px = wx * tiles_count
  py = wy * tiles_count
  return [px.to_i, py.to_i]
end

to_tile() click to toggle source

calculates the tile numbers for google maps at the given zoom level

# File lib/simple_mercator_location.rb, line 128
def to_tile
  px,py = self.to_px

  tx = Rational(px, tile_size).to_i
  ty = Rational(py, tile_size).to_i

  return [tx,ty]
end

to_w() click to toggle source

calculates the google world-coordinates as described here: developers.google.com/maps/documentation/javascript/examples/map-coordinates

# File lib/simple_mercator_location.rb, line 109
def to_w
  px = origin_px.first +  pixel_per_rad * lon_rad
  py = origin_px.last  -  pixel_per_rad * lat_scaled_rad

  return [px, py]
end

zoom_at(scale) click to toggle source

set the zoom-level and returns self

# File lib/simple_mercator_location.rb, line 55
def zoom_at(scale)
    @zoom = scale
    self
end