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!! NEMO/OCE 4.0 , NEMO Consortium (2018)
!! $Id: grt_cir_dis.h90 13226 2020-07-02 14:24:31Z orioltp $
!! Software governed by the CeCILL license (see ./LICENSE)
!!----------------------------------------------------------------------
REAL(KIND=wp) FUNCTION grt_cir_dis( pa1, pa2, pb1, pb2, pc1, pc2 )
!!----------------------------------------------------------------------
!! *** FUNCTION grt_cir_dis ***
!!
!! ** Purpose : Great circle distance between pts (lat1,lon1)
!! & (lat2,lon2)
!!
!! ** Method : Geometry.
!!
!! History :
!! ! 1995-12 (G. Madec, E. Durand, A. Weaver, N. Daget) Original
!! ! 2006-03 (A. Vidard) Migration to NEMOVAR
!! ! 2006-10 (A. Weaver) Cleanup
!!----------------------------------------------------------------------
!! * Arguments
REAL(KIND=wp) :: pa1 ! sin(lat1)
REAL(KIND=wp) :: pa2 ! sin(lat2)
REAL(KIND=wp) :: pb1 ! cos(lat1) * cos(lon1)
REAL(KIND=wp) :: pb2 ! cos(lat2) * cos(lon2)
REAL(KIND=wp) :: pc1 ! cos(lat1) * sin(lon1)
REAL(KIND=wp) :: pc2 ! cos(lat2) * sin(lon2)
REAL(KIND=wp) :: cosdist ! cosine of great circle distance
! Compute cosine of great circle distance, constraining it to be between
! -1 and 1 (rounding errors can take it slightly outside this range
cosdist = MAX( MIN( pa1 * pa2 + pb1 * pb2 + pc1 * pc2, 1.0_wp), -1.0_wp )
grt_cir_dis = &
& ASIN( SQRT( 1.0_wp - cosdist**2.0_wp ) )
END FUNCTION grt_cir_dis