Class: SwedishGrid

Inherits:
Object
  • Object
show all
Defined in:
lib/swedishgrid.rb

Instance Method Summary collapse

Constructor Details

#initialize(grid) ⇒ SwedishGrid

Returns a new instance of SwedishGrid.



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# File 'lib/swedishgrid.rb', line 3

def initialize(grid)
  case grid
  when :rt90
    # rt90_2.5_gon_v
    @axis = 6378137.0
    @flattening = 1.0 / 298.257222101
    @central_meridian = 15.806284529
    @lat_of_origin = 0.0
    @scale = 1.00000561024
    @false_northing = -667.711
    @false_easting = 1500064.274 
  when :sweref99tm
    @axis = 6378137.0
    @flattening = 1.0 / 298.257222101
    @central_meridian = 15.00 
    @lat_of_origin = 0.0
    @scale = 0.9996
    @false_northing = 0.0
    @false_easting = 500000.0
  else
    raise "Unknown grid"
  end
end

Instance Method Details

#geodetic_to_grid(latitude, longitude) ⇒ Object

Conversion from geodetic coordinates to grid coordinates.



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# File 'lib/swedishgrid.rb', line 70

def geodetic_to_grid(latitude, longitude)
  # Prepare ellipsoid-based stuff.
  e2 = @flattening * (2.0 - @flattening)
  n = @flattening / (2.0 - @flattening)
  a_roof = @axis / (1.0 + n) * (1.0 + n*n/4.0 + n*n*n*n/64.0)
  a = e2
  b = (5.0*e2*e2 - e2*e2*e2) / 6.0
  c = (104.0*e2*e2*e2 - 45.0*e2*e2*e2*e2) / 120.0
  d = (1237.0*e2*e2*e2*e2) / 1260.0
  beta1 = n/2.0 - 2.0*n*n/3.0 + 5.0*n*n*n/16.0 + 41.0*n*n*n*n/180.0
  beta2 = 13.0*n*n/48.0 - 3.0*n*n*n/5.0 + 557.0*n*n*n*n/1440.0
  beta3 = 61.0*n*n*n/240.0 - 103.0*n*n*n*n/140.0
  beta4 = 49561.0*n*n*n*n/161280.0

  # Convert.
  deg_to_rad = Math::PI / 180.0
  phi = latitude * deg_to_rad
  lambda = longitude * deg_to_rad
  lambda_zero = @central_meridian * deg_to_rad

  phi_star = phi - Math.sin(phi) * Math.cos(phi) * (a + 
          b*(Math.sin(phi) ** 2) +
          c*(Math.sin(phi) ** 4) +
          d*(Math.sin(phi) ** 6))
  delta_lambda = lambda - lambda_zero
  xi_prim = Math.atan(Math.tan(phi_star) / Math.cos(delta_lambda))
  eta_prim = Math.atanh(Math.cos(phi_star) * Math.sin(delta_lambda))
  x = @scale * a_roof * (xi_prim +
          beta1 * Math.sin(2.0*xi_prim) * Math.cosh(2.0*eta_prim) +
          beta2 * Math.sin(4.0*xi_prim) * Math.cosh(4.0*eta_prim) +
          beta3 * Math.sin(6.0*xi_prim) * Math.cosh(6.0*eta_prim) +
          beta4 * Math.sin(8.0*xi_prim) * Math.cosh(8.0*eta_prim)) +
          @false_northing
  y = @scale * a_roof * (eta_prim +
          beta1 * Math.cos(2.0*xi_prim) * Math.sinh(2.0*eta_prim) +
          beta2 * Math.cos(4.0*xi_prim) * Math.sinh(4.0*eta_prim) +
          beta3 * Math.cos(6.0*xi_prim) * Math.sinh(6.0*eta_prim) +
          beta4 * Math.cos(8.0*xi_prim) * Math.sinh(8.0*eta_prim)) +
          @false_easting
  return [(x * 1000.0).round / 1000.0, (y * 1000.0).round / 1000.0]
end

#grid_to_geodetic(x, y) ⇒ Object

Conversion from grid coordinates to geodetic coordinates.



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# File 'lib/swedishgrid.rb', line 28

def grid_to_geodetic(x, y)
  # Prepare ellipsoid-based stuff.
  e2 = @flattening * (2.0 - @flattening)
  n = @flattening / (2.0 - @flattening)
  a_roof = @axis / (1.0 + n) * (1.0 + n*n/4.0 + n*n*n*n/64.0)
  delta1 = n/2.0 - 2.0*n*n/3.0 + 37.0*n*n*n/96.0 - n*n*n*n/360.0
  delta2 = n*n/48.0 + n*n*n/15.0 - 437.0*n*n*n*n/1440.0
  delta3 = 17.0*n*n*n/480.0 - 37*n*n*n*n/840.0  
  delta4 = 4397.0*n*n*n*n/161280.0

  astar = e2 + e2*e2 + e2*e2*e2 + e2*e2*e2*e2
  bstar = -(7.0*e2*e2 + 17.0*e2*e2*e2 + 30.0*e2*e2*e2*e2) / 6.0
  cstar = (224.0*e2*e2*e2 + 889.0*e2*e2*e2*e2) / 120.0
  dstar = -(4279.0*e2*e2*e2*e2) / 1260.0

  # Convert.
  deg_to_rad = Math::PI / 180  
  lambda_zero = @central_meridian * deg_to_rad
  xi = (x - @false_northing) / (@scale * a_roof)
  eta = (y - @false_easting) / (@scale * a_roof)
  xi_prim = xi - 
          delta1*Math.sin(2.0*xi) * Math.cosh(2.0*eta) - 
          delta2*Math.sin(4.0*xi) * Math.cosh(4.0*eta) - 
          delta3*Math.sin(6.0*xi) * Math.cosh(6.0*eta) - 
          delta4*Math.sin(8.0*xi) * Math.cosh(8.0*eta)  
  eta_prim = eta - 
          delta1*Math.cos(2.0*xi) * Math.sinh(2.0*eta) - 
          delta2*Math.cos(4.0*xi) * Math.sinh(4.0*eta) - 
          delta3*Math.cos(6.0*xi) * Math.sinh(6.0*eta) - 
          delta4*Math.cos(8.0*xi) * Math.sinh(8.0*eta)  
  phi_star = Math.asin(Math.sin(xi_prim) / Math.cosh(eta_prim))  
  delta_lambda = Math.atan(Math.sinh(eta_prim) / Math.cos(xi_prim))
  lng_radian = lambda_zero + delta_lambda  
  lat_radian = phi_star + Math.sin(phi_star) * Math.cos(phi_star) *
          (astar + 
           bstar*(Math.sin(phi_star) ** 2) + 
           cstar*(Math.sin(phi_star) ** 4) + 
           dstar*(Math.sin(phi_star) ** 6))
  return [lat_radian * 180.0 / Math::PI, lng_radian * 180.0 / Math::PI]
end