!c****************************************************************
!c
!c       Various curvature functions
!c 
!c
!c****************************************************************
!c**
!c**	FILE NAME: curvature.f
!c**
!c**     DATE WRITTEN: 12/02/93
!c**
!c**     PROGRAMMER:Scott Hensley
!c**
!c** 	FUNCTIONAL DESCRIPTION: This routine computes the curvature for 
!c**     of various types required for ellipsoidal or spherical earth 
!c**     calculations.  
!c**
!c**     ROUTINES CALLED: none
!c**  
!c**     NOTES: none
!c**
!c**     UPDATE LOG:
!c**
!c*****************************************************************

        real*8 function reast(r_a,r_e2,r_lat)

       	implicit none
        real*8 r_a,r_e2,r_lat
        
        reast = r_a/sqrt(1.d0 - r_e2*sin(r_lat)**2) 
      
        end  

        real*8 function rnorth(r_a,r_e2,r_lat)

       	implicit none
        real*8 r_a,r_e2,r_lat
        
        rnorth = (r_a*(1.d0 - r_e2))/(1.d0 - r_e2*sin(r_lat)**2)**(1.5d0) 

        end

        real*8 function rdir(r_a,r_e2,r_hdg,r_lat)

       	implicit none
        real*8 r_a,r_e2,r_lat,r_hdg,r_re,r_rn,reast,rnorth
        
        r_re = reast(r_a,r_e2,r_lat)
        r_rn = rnorth(r_a,r_e2,r_lat)

        rdir = (r_re*r_rn)/(r_re*cos(r_hdg)**2 + r_rn*sin(r_hdg)**2) 

        end