subroutine distk(rlon1, rlat1, rlon2, rlat2, dx, dy, rad)
! This routine calculates the distance in km (rad) between the
! points (rlon1,rlat1) and (rlon2,rlat2) using an approximate
! formula. The lon and lat are in deg E and N. The east and
! north components of the distance (dx,dy) are also calculated.

! Modifications:
!   4/26/21 (J. Dostalek) Started this Fortran 90 version
!-------------------------------------------------------------------------------

  implicit none

  real, intent(in) :: rlon1
  real, intent(in) :: rlat1
  real, intent(in) :: rlon2
  real, intent(in) :: rlat2

  real, intent(out) :: dx
  real, intent(out) :: dy
  real, intent(out) :: rad

  real, parameter :: dtk = 111.1
  real, parameter :: dtr = 0.0174533
  real :: cfac

  cfac = cos(0.5*dtr*(rlat1 + rlat2))

  dx  = dtk*(rlon2 - rlon1)*cfac
  dy  = dtk*(rlat2 - rlat1)
  rad = sqrt(dx*dx + dy*dy)

  return
end subroutine distk