! First include the set of model-wide compiler flags 
#include "tm5.inc"

module misctools

  implicit none

  private

  public :: dist

contains
  !---------------------
  !  subroutine dist
  !     compute distance between points on the globe
  !---------------------

  subroutine dist( x1g, y1g, x2g, y2g, ddg )
    !---------------------------------------------------------------
    !!!   compute distance of two points on the globe.
    !
    !!!   this formula is correct, also for points close together.
    !
    !!!   x1g, y1g : longitude and latitude of first point  (degrees)
    !!!   x2g, y2g : longitude and latitude of second point (degrees)
    !!!   ddg      : distance between these points          (km)
    !----------------------------------------------------------------
    implicit  none
    !
    real,intent(in) :: x1g, x2g, y1g, y2g
    real,intent(out) :: ddg
    !
    real :: x1, x2, y1, y2, dd
    real :: cc, dx, dy, dx2, dy2, dd2
    real,parameter ::  pi=3.141593, rearth=6378.5
    !
    cc = pi / 180.0
    !
    x1 = x1g * cc
    x2 = x2g * cc
    y1 = y1g * cc
    y2 = y2g * cc
    !
    !      print *,'x1,x2,y1,y2', x1,x2,y1,y2
    dy = 0.5 * ( y2 - y1 )
    dy = sin(dy)
    dy2 = dy * dy
    !
    dx = 0.5 * ( x2 - x1 )
    dx = sin(dx)
    dx2 = dx * dx * cos(y1) * cos(y2)
    !
    !     print *,'dx,dy,dx2,dy2',dx,dy,dx2,dy2
    dd2 = dx2 + dy2
    dd = sqrt(dd2)
    dd = 2.0 * asin(dd)
    !
    ddg = dd / cc
    ddg = (ddg * 2.0 * pi * rearth) / 360.0
    !     print *,'dd2,dd,ddg', dd2,dd,ddg
    !
  end subroutine dist

end module misctools