CTITLESALMPAI -- UNIFORM RESAMPLING USING POLYNOMIAL FITTING
C***********************************************************************
C                 COPYRIGHT ATLANTIC RICHFIELD COMPANY 1991            *
C***********************************************************************
CABS  SALMPAI - UNIFORM RESAMPLING USING POLYNOMIAL FITTING
CA
CSUBROUTINE SALMPAI
C
C     SUBROUTINE SALMPAI (X,Y,NX,ID,TA,S,YY,NYY)
C
C     COPYRIGHT ATLANTIC RICHFIELD COMPANY 1991.
C
C     ALL RIGHTS RESERVED.  NO PART OF THIS PROGRAM MAY BE PHOTOCOPIED,
C     REPRODUCED, OR  TRANSLATED TO ANOTHER PROGRAM LANGUAGE WITHOUT THE
C     PRIOR CONSENT OF ATLANTIC RICHFIELD COMPANY.
C
CA    AUTHOR                      DAVE THOMPSON
CA    DESIGNER                    DAVE THOMPSON
CA    LANGUAGE                    FORTRAN H
CA    SYSTEM                      S/370
C     WRITTEN                     UNKNOWN
CA
CA    PURPOSE OF PROGRAM:
CA
CA    THIS SUBROUTINE DOES UNIFORM RESAMPLING USING POLYNOMIAL FITTING.
CA    YOU MUST SPECIFY THE DEGREE OF POLYNOMIAL YOU ARE USING. IT
CA    RESAMPLES USING UNIFORMED SPACING.
CA
CA
CA    CALLING SEQUENCE:
CA
CA    CALL SALMPAI (X,Y,NX,ID,TA,S,YY,NYY)
CA
CA    IN    X  R4   INDEPENDENT VARIABLE WITH NX VALUES.
CA    IN    Y  R4   DEPENDENT VARIABLE
CA    IN   NX  I4   NUMBER OF SAMPLES IN X AND Y
CA    IN   ID  I4   DEGREE OF POLYNOMIAL
CA    IN   TA  R4   X VALUE OF FIRST INTERPOLATION POSITION
CA    IN    S  R4   SAMPLE PERIOD OF UNIFORM INTERPOLATION
CA    OUT  YY  R4   OUTPUT WITH NYY VALUES
CA    IN  NYY  I4   THE NUMBER OF SAMPLES TO RETURN IN YY
CA
CA
CA    SUBROUTINES CALLED:   SALMPAP
C
CA    EJECT
CAEND
C**********************************************************************
C
C     LOCAL VARIABLES
C
C     IDD        I*4        TEMPORARY VARIABLE USED TO STORE THE POWER
C                           OF THE POLYNOMIAL WHICH CAN BE RESET BASED
C                           ON THE NUMBER OF TRACES IN THE GATHER BEING
C                           USED FOR ANGLE ANALYSIS.
C     J          I*4        USED AS INDEX INTO INDEPENDENT VARIABLE
C                           ARRAY FOR START OF INTERPOLATION.
C     P          R*4        TEMPORARY AVERAGE USED FOR RESAMPLING.
C     PP         R*4        TEMPORARY AVERAGE USED FOR RESAMPLING.
C     T          R*4        LOCAL VARIABLE USED TO HOLD THE INPUT X
C                           VALUE WHERE INTERPOLATION IS DESIRED.
C
      SUBROUTINE SALMPAI(X,Y,NX,ID,TA,S,YY,NYY)
      IMPLICIT INTEGER (A-Z)
C
      REAL      X(1),Y(1),YY(1)
      REAL      P,PP,S,T,TA
C
      IDD = ID
      IF (NX .LT. ID+1) IDD = NX - 1
      J = 1
      NNX = NX - IDD
      T = TA
      DO 140 I = 1, NYY
 100     CONTINUE
         IF (J .EQ. NNX) GO TO 120
         P = (X(J) + X(J + ID) )  * .5
         PP = (X(J + 1) + X(J + ID + 1) )  * .5
         IF (ABS ( T - P )  .LE. ABS ( T-PP ) ) GO TO 120
         J = J + 1
         GO TO 100
 120     CONTINUE
C
         IF (T .LT. X(J)) THEN
            YY(I) = Y(J)
         ELSE
            IF (T .GT. X(J+IDD)) THEN
               YY(I) = Y(J + IDD)
            ELSE
               CALL SALMPAP ( X(J), Y(J), T, YY(I), IDD)
            ENDIF
         ENDIF
C
         T = T + S
 140  CONTINUE
C
      RETURN
      END