PROGRAM ETOPO2v2g_to_GRD
   !by Peter Bird, UCLA, 2022.11.16
    IMPLICIT NONE
    INTEGER*2, DIMENSION(5401, 10801) :: DEM_meters
    INTEGER :: i, j, k, k1, k2
    CHARACTER*8 :: elevation
    CHARACTER*240 :: group_of_30 ! or, 31 (at end of each row)

    OPEN (UNIT = 1, FILE = "ETOPO2v2g_i2_MSB.bin", STATUS = "OLD", ACTION = "READ", FORM = "BINARY", CONVERT = "BIG_ENDIAN")
    READ (UNIT = 1) ((DEM_meters(i, j), j = 1, 10801), i = 1, 5401)
    CLOSE (1)

    OPEN (UNIT = 2, FILE = "ETOPO2v2g.grd")
    WRITE (2, "('-180.0  0.0333333  +180.0  ETOPO2v2g  [NOAA National Geophysical Data Center, 2006]')")
    WRITE (2, "(' -90.0  0.0333333   +90.0  from NOAA, specifically from NCEI (formerly NGDC) in 2022')")
    DO i = 1, 5401 ! rows, N to S, 2 arc-minutes apart
        group_of_30 = ' ' ! initialize as empty
        DO j = 1, 360 ! degrees of longitude, running East from -180
            k2 = j * 30 ! most groups have a length of 30 elevations (1 degree)
            k1 = k2 - 29
            IF (j == 360) k2 = k2 + 1 ! creating a group of 31 (including redundant IDL-seam end-cap)
            DO k = k1, k2
                WRITE (elevation, *) DEM_meters(i, k)
                elevation = ADJUSTL(elevation)
                IF (k == k1) THEN
                    group_of_30 = TRIM(elevation)
                ELSE
                    group_of_30 = TRIM(group_of_30) // ' ' // TRIM(elevation)
                END IF
            END DO
            WRITE (2, "(A)") TRIM(group_of_30)
        END DO
    END DO
    CLOSE (2)
END PROGRAM ETOPO2v2g_to_GRD