docs: def CalcRad(lat):
      "Radius of curvature in meters at specified latitude."
      a = 6378.137
      e2 = 0.081082 * 0.081082
      # the radius of curvature of an ellipsoidal Earth in the plane of a
      # meridian of latitude is given by
      #
      # R' = a * (1 - e^2) / (1 - e^2 * (sin(lat))^2)^(3/2)
      #
      # where a is the equatorial radius,
      # b is the polar radius, and
      # e is the eccentricity of the ellipsoid = sqrt(1 - b^2/a^2)
      #
      # a = 6378 km (3963 mi) Equatorial radius (surface to center distance)
      # b = 6356.752 km (3950 mi) Polar radius (surface to center distance)
      # e = 0.081082 Eccentricity
      sc = math.sin(Deg2Rad(lat))
      x = a * (1.0 - e2)
      z = 1.0 - e2 * sc * sc
      y = pow(z, 1.5)
      r = x / y
  
      r = r * 1000.0      # Convert to meters
      return r