Simple Data Access Example in FORTRAN

The following program reads through the first lane of a mapping data set, and reports the largest pixel value found. It assumes the dataset has the charactersitics listed in the above example header file, and that the program is to be compiled and run on a DEC ALPHA.

Note that this example assumes RECL is in bytes. This assumption is dependent upon FORTRAN compiler options.

      INTEGER*2 BUFFER(1280)
      INTEGER*2 MAXVAL
      INTEGER STATUS
      INTEGER J
      INTEGER INREC

      OPEN ( UNIT=1, FILE='l1', STATUS='OLD', ACCESS='DIRECT',
     :  FORM='UNFORMATTED', RECL=2560 )

      INREC = 0
      STATUS = 0
      MAXVAL = -32767
*
*   Read one row of pixels at a time updating the maximum transmission
*   value
*
      DO WHILE ( STATUS .EQ. 0 )
         INREC = INREC + 1
         READ ( UNIT=1, REC = INREC, IOSTAT=STATUS ) BUFFER
         IF ( STATUS .EQ. 0 ) THEN
            DO J = 1, 1280
               MAXVAL = MAX(BUFFER(J), MAXVAL)
            ENDDO
         ENDIF
      ENDDO

      PRINT *, 'Maximum transmission found was', MAXVAL

      CLOSE ( UNIT=1 )

      END