gistfile1.builder

def Math.pow(x,y)
  x**y
end

## Converts from utm to lat_lng. Default zone is the one in which
## Oslo and Akershus falls.
def utm_to_lat_lng(easting, northing, zone=32, northernHemisphere=true)
  if not northernHemisphere then
    northing = 10000000 - northing
  end
  a = 6378137
  e = 0.081819191
  e1sq = 0.006739497
  k0 = 0.9996

  arc = northing / k0
  mu = arc / (a * (1 - Math.pow(e, 2) / 4.0 - 3 * Math.pow(e, 4) / 64.0 - 5 * Math.pow(e, 6) / 256.0))

  ei = (1 - Math.pow((1 - e * e), (1 / 2.0))) / (1 + Math.pow((1 - e * e), (1 / 2.0)))

  ca = 3 * ei / 2 - 27 * Math.pow(ei, 3) / 32.0

  cb = 21 * Math.pow(ei, 2) / 16 - 55 * Math.pow(ei, 4) / 32
  cc = 151 * Math.pow(ei, 3) / 96
  cd = 1097 * Math.pow(ei, 4) / 512
  phi1 = mu + ca * Math.sin(2 * mu) + cb * Math.sin(4 * mu) + cc * Math.sin(6 * mu) + cd * Math.sin(8 * mu)

  n0 = a / Math.pow((1 - Math.pow((e * Math.sin(phi1)), 2)), (1 / 2.0))

  r0 = a * (1 - e * e) / Math.pow((1 - Math.pow((e * Math.sin(phi1)), 2)), (3 / 2.0))
  fact1 = n0 * Math.tan(phi1) / r0

  _a1 = 500000 - easting
  dd0 = _a1 / (n0 * k0)
  fact2 = dd0 * dd0 / 2

  t0 = Math.pow(Math.tan(phi1), 2)
  q0 = e1sq * Math.pow(Math.cos(phi1), 2)

  fact3 = (5 + 3 * t0 + 10 * q0 - 4 * q0 * q0 - 9 * e1sq) * Math.pow(dd0, 4) / 24

  fact4 = (61 + 90 * t0 + 298 * q0 + 45 * t0 * t0 - 252 * e1sq - 3 * q0 * q0) * Math.pow(dd0, 6) / 720

  lof1 = _a1 / (n0 * k0)
  lof2 = (1 + 2 * t0 + q0) * Math.pow(dd0, 3) / 6.0
  lof3 = (5 - 2 * q0 + 28 * t0 - 3 * Math.pow(q0, 2) + 8 * e1sq + 24 * Math.pow(t0, 2)) * Math.pow(dd0, 5) / 120
  _a2 = (lof1 - lof2 + lof3) / Math.cos(phi1)
  _a3 = _a2 * 180 / Math::PI

  latitude = 180 * (phi1 - fact1 * (fact2 + fact3 + fact4)) / Math::PI

  if not northernHemisphere then
    latitude = -latitude
  end
  longitude = ((zone > 0) and (6 * zone - 183.0) or 3.0) - _a3

  return [latitude, longitude]
end