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! (C) Copyright 2005- ECMWF.
!
! This software is licensed under the terms of the Apache Licence Version 2.0
! which can be obtained at http://www.apache.org/licenses/LICENSE-2.0.
!
! In applying this licence, ECMWF does not waive the privileges and immunities granted to it by
! virtue of its status as an intergovernmental organisation nor does it submit to any jurisdiction.
!
!
! Description: How to control decimal precision when packing GRIB fields.
!
!
!
program precision
use eccodes
implicit none
integer(kind=4) :: size1
integer :: infile, outfile
integer :: igrib
real(kind=8), dimension(:), allocatable :: values1
real(kind=8), dimension(:), allocatable :: values2
real(kind=8) :: maxa, a, maxv, minv, maxr, r=0
integer(kind=4) :: decimalPrecision, bitsPerValue1, bitsPerValue2
integer :: i, iret
call codes_open_file(infile, &
'../../data/regular_latlon_surface_constant.grib1', 'r')
call codes_open_file(outfile, &
'../../data/regular_latlon_surface_prec.grib1', 'w')
! a new grib message is loaded from file
! igrib is the grib id to be used in subsequent calls
call codes_grib_new_from_file(infile, igrib)
! bitsPerValue before changing the packing parameters
call codes_get(igrib, 'bitsPerValue', bitsPerValue1)
! get the size of the values array
call codes_get_size(igrib, "values", size1)
allocate (values1(size1), stat=iret)
allocate (values2(size1), stat=iret)
! get data values before changing the packing parameters
call codes_get(igrib, "values", values1)
! setting decimal precision=2 means that 2 decimal digits
! are preserved when packing.
decimalPrecision = 2
call codes_set(igrib, "changeDecimalPrecision", decimalPrecision)
! bitsPerValue after changing the packing parameters
call codes_get(igrib, "bitsPerValue", bitsPerValue2)
! get data values after changing the packing parameters
call codes_get(igrib, "values", values2)
! computing error
maxa = 0
maxr = 0
maxv = values2(1)
minv = maxv
do i = 1, size1
a = abs(values2(i) - values1(i))
if (values2(i) .gt. maxv) maxv = values2(i)
if (values2(i) .lt. maxv) minv = values2(i)
if (values2(i) .ne. 0) then
r = abs((values2(i) - values1(i))/values2(i))
end if
if (a .gt. maxa) maxa = a
if (r .gt. maxr) maxr = r
end do
write (*, *) "max absolute error = ", maxa
write (*, *) "max relative error = ", maxr
write (*, *) "min value = ", minv
write (*, *) "max value = ", maxv
write (*, *) "old number of bits per value=", bitsPerValue1
write (*, *) "new number of bits per value=", bitsPerValue2
! write modified message to a file
call codes_write(igrib, outfile)
call codes_release(igrib)
call codes_close_file(infile)
call codes_close_file(outfile)
deallocate (values1)
deallocate (values2)
end program precision
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