C++*********************************************************************
C
C CENT_3.F
C         REAL(KIND=R_8)     :: C,S,P,T,FI            July 2005 A. Leith
C
C **********************************************************************
C=* FROM: SPIDER - MODULAR IMAGE PROCESSING SYSTEM.   AUTHOR: J.FRANK  *
C=* Copyright (C) 1985-2005  Health Research Inc.                      *
C=*                                                                    *
C=* HEALTH RESEARCH INCORPORATED (HRI),                                *   
C=* ONE UNIVERSITY PLACE, RENSSELAER, NY 12144-3455.                   *
C=*                                                                    *
C=* Email:  spider@wadsworth.org                                       *
C=*                                                                    *
C=* This program is free software; you can redistribute it and/or      *
C=* modify it under the terms of the GNU General Public License as     *
C=* published by the Free Software Foundation; either version 2 of the *
C=* License, or (at your option) any later version.                    *
C=*                                                                    *
C=* This program is distributed in the hope that it will be useful,    *
C=* but WITHOUT ANY WARRANTY; without even the implied warranty of     *
C=* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU  *
C=* General Public License for more details.                           *
C=*                                                                    *
C=* You should have received a copy of the GNU General Public License  *
C=* along with this program; if not, write to the                      *
C=* Free Software Foundation, Inc.,                                    *
C=* 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.      *
C=*                                                                    *
C **********************************************************************
C
C
C  PURPOSE: PHASE APPROXIMATION TO CENTER OF GRAVITY
C
C--*********************************************************************

         SUBROUTINE  CENT_3(LUN,NSAM,NROW,NSLICE,SNS,SNR,SNC)

         DIMENSION  B(NSAM),X(NSAM),Y(NROW),Z(NSLICE)

         INTEGER, PARAMETER :: R_8 = SELECTED_REAL_KIND(P=8)
         REAL(KIND=R_8)     :: C,S,P,T,FI

         X = 0.0
         Y = 0.0
         Z = 0.0
        
         DO K=1,NSLICE
            DO J=1,NROW
               CALL REDLIN(LUN,B,NSAM,J+(K-1)*NROW)
               T    = SUM(B)
               X    = X + B
               Y(J) = Y(J) + T
               Z(K) = Z(K) + T
            ENDDO
         ENDDO
         C = 0.0
         S = 0.0
         P = 8 * DATAN(1.0D0) / NSAM

         DO I=1,NSAM
            C = C + COS(P * (I-1)) * X(I)
            S = S + SIN(P * (I-1)) * X(I)
         ENDDO

         FI = ATAN2(S,C)
         IF (FI .LT. 0.0)  FI = FI + 8 * DATAN(1.0D0)
         SNS = FI / P + 1.0
C
         C = 0.0
         S = 0.0
         P = 8 * DATAN(1.0D0) / NROW

         DO    J=1,NROW
            C = C + COS(P * (J-1)) * Y(J)
            S = S + SIN(P * (J-1)) * Y(J)
         ENDDO

         FI = ATAN2(S,C)
         IF (FI.LT.0.0)  FI = FI + 8 * DATAN(1.0D0)
         SNR=FI/P+1.0

         C = 0.0
         S = 0.0
         P = 8 * DATAN(1.0D0) / NSLICE

         DO K=1,NSLICE
            C = C + COS(P * (K-1)) * Z(K)
            S = S + SIN(P * (K-1)) * Z(K)
         ENDDO

         FI = ATAN2(S,C)
         IF (FI .LT. 0.0)  FI = FI + 8 * DATAN(1.0D0)

         SNC = FI / P + 1.0

         END