SUBROUTINE READ_NVAP(FLNAME,IFLD,ISTAT)
C
C********************************************************************
C
C  THIS ROUTINE READS IN THE NVAP DATA IN CIRA CLIMATE DATA FORMAT.
C  IT ASSUMES THAT ALL FIELDS IN THE FILE HAVE THE SAME SIZE WITH
C  RESOLUTION = 360X180, (1 DEGREE GLOBAL RESOLUTION)
C
C  WRITTEN BY DAVE RANDEL CIRA/CSU
C          IN OCTOBER, 1994
C
C               INPUT PARAMETERS        FLNAME*  : DATA FILENAME
c                                       IFLD     : FIELD NUMBER
C
C              OUTPUT PARAMETERS        ISTAT    : STATUS CODE
C
C********************************************************************
C
       CHARACTER FLNAME*(*)
       INTEGER*4 IFLD,IDT,ISTAT
C
       CHARACTER TAPEC*4
       REAL*4 OFFSET,SCALE
       CHARACTER BLANK6*6, BLANK5*5, HEADBUFF*144

       BYTE BYTEBUFF(720)
       REAL*4 DATBUFF(360)
C
C--------COMMON BLOCK WHICH HOLDS THE DATA AND HEADER INFORMATION---------
C
       REAL DATA(360,180), HEADR(4), ZINDEF
       INTEGER*2 HEADI(11)
       CHARACTER LABEL*40
       COMMON /GRDDATA/ DATA,HEADR,ZINDEF,HEADI,LABEL,OFFSET, SCALE
C
C-------------------------------------------------------------------------
C
       ISTAT = -1
       IXSIZE = 360
       IYSIZE = 180
C
C** SET INTERGER SWAPPING TYPE AND RECL IN OPEN ***********
C                                                        !*
c      IDT = 1       ! INT*2  TESTED ON VAX VMS          !*
       IDT = 2       ! INT*2 - TESTED ON HP or PC        !*
C       IDT = 3       ! INT*2 - TESTED ON SGI             !*
C                                                        !*
C**********************************************************
C
C**OPEN INPUT DATA FILE
C
       IF(IDT .EQ. 1) THEN
           OPEN(UNIT=101,FILE=FLNAME,FORM='UNFORMATTED',
     >       ACCESS='DIRECT', STATUS='OLD', ERR=90, RECL=180)    !FOR VAX
       ELSEIF(IDT .EQ. 2) THEN
           OPEN(UNIT=101,FILE=FLNAME,FORM='UNFORMATTED',
     >       ACCESS='DIRECT', STATUS='OLD', ERR=90, RECL=720)    !FOR HP
       ELSEIF(IDT .EQ. 3) THEN
           OPEN(UNIT=101,FILE=FLNAME,FORM='UNFORMATTED',
     >       ACCESS='DIRECT', STATUS='OLD', ERR=90, RECL=180)    !FOR SGI
       ENDIF
C
C**COMPUTE STARTING HEADER RECORD FROM INPUT FIELD NUMBER AND FIELD SIZE
C
       ISHEAD  = ( (IFLD-1) * (IYSIZE+1) ) + 1
C
C**READ IN REQUESTED FIELD HEADER
C
       READ(101,REC=ISHEAD,ERR=91) HEADBUFF
       READ(HEADBUFF,11)TAPEC,(HEADI(J),J=1,3),BLANK5,
     >            (HEADI(J),J=4,11),
     >            (HEADR(J),J=1,4),
     >            OFFSET, SCALE, ZINDEF, BLANK6, LABEL
C
 11    FORMAT( A4, I3, I3, I1, A5,
     >         I2, I3, I2, I2, I3, I2,
     >         I4, I4, F6.2, F6.2, F7.3, F8.3,
     >         E11.5, E11.5, E11.5, A6, A40)
C
c**INITIALIZE DATA ARRAY WITH ZINDEF VALUES
c
       DO I = 1,180
         DO J = 1,360
           DATA(J,I) = ZINDEF
         ENDDO
       ENDDO
C
C**READ IN 720 BYTE DATA RECORDS, CONVERT TO REALS, FILL OUTPUT DATA ARRAY
C
       DO I = 1,IYSIZE
         READ(101,REC=ISHEAD+I,ERR=92)(BYTEBUFF(J), J = 1,720)
         CALL CCDA_CONVRTDT(BYTEBUFF, IDT, HEADI(10), OFFSET, ZINDEF,
     >                                SCALE, DATBUFF)
         DO J = 1, IXSIZE
           DATA(J,I) = DATBUFF(J)
         ENDDO
       ENDDO
C
C**CLOSE FILE AND RETURN
C
       ISTAT = 0
       CLOSE(UNIT=101)
       RETURN
C
C**ERROR FOUND
C
 90    WRITE(6,*)'ERROR OPENING FILE'
       ISTAT = -1
       RETURN
 91    WRITE(6,*)'    ERROR READING REQUESTED HEADER REC', ISHEAD
       WRITE(6,*)' ERROR MAY SIMPLY BE THAT LAST FIELD HAS BEEN READ'
       ISTAT = -3
       CLOSE(UNIT=101)
       RETURN
 92    WRITE(6,*)'ERROR READING REQUESTED DATA'
       ISTAT = -4
       CLOSE(UNIT=101)
       RETURN
       END
C
C--------------------------------------------------------------------------
C
      SUBROUTINE CCDA_CONVRTDT(BBUF, IDT, NUMVAL, OFFSET, ZINDEF,
     >                         SCALE, DBUF)
C
C***************************************************************************
C
C   THIS ROUTINE TAKES THE BYTE ARRAY AND USING THE INPUT DATA_TYPE PUTS
C   ALL THE DATA IN THE RECORD INTO THE REAL ARRAY DBUF. THIS DOES THE
C   NECESSARY BYTE SWAPPING.
C
C   WRITTEN BY DAVE RANDEL CIRA/CSU
C           IN JUNE 1992
C
C***************************************************************************
C
        REAL*4  DBUF(360), OFFSET, SCALE, ZINDEF
        BYTE BBUF(720), B2A(2)
        INTEGER*2 INT2, NUMVAL
        integer*4 IDT
        EQUIVALENCE(INT2, B2A)
C
        IF(NUMVAL .EQ. 0) THEN
             WRITE(6,*)'FROM CONVRT: NUMBER OF POINTS = 0 '
             STOP 99
        ENDIF
        IF(IDT .EQ. 1) THEN                          !I*2
             DO I = 1,NUMVAL
               ISB = (I-1)*2 + 1
               B2A(1) = BBUF(0+ISB)
               B2A(2) = BBUF(1+ISB)
               IF(FLOAT(INT2) .EQ. ZINDEF) THEN
                       DBUF(I) = ZINDEF
               ELSE
                       DBUF(I) = (FLOAT(INT2) * SCALE) + OFFSET
               ENDIF
             ENDDO
C
        ELSEIF(IDT.EQ.2 .OR. IDT.EQ.3) THEN          !I*2 NEEDING BYTE SWAP
             DO I = 1,NUMVAL
               ISB = (I-1)*2 + 1
               B2A(1) = BBUF(1+ISB)
               B2A(2) = BBUF(0+ISB)
               IF(FLOAT(INT2) .EQ. ZINDEF) THEN
                       DBUF(I) = ZINDEF
               ELSE
                       DBUF(I) = (FLOAT(INT2) * SCALE) + OFFSET
               ENDIF
             ENDDO
        ELSE
             WRITE(6,*)'DATA TYPE CONVERSION NOT SUPPORTED '
             STOP 99
        ENDIF
C
C
      RETURN
      END