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language | none |
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title | grib_precision.f90 |
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linenumbers | false |
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| ! (C) Copyright 2005-2017 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 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
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))
endif
if ( a .gt. maxa ) maxa=a
if ( r .gt. maxr ) maxr=r
enddo
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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language | cpp |
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title | grib_precision.c |
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linenumbers | false |
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| /*
* (C) Copyright 2005-2017 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.
*/
/*
* C Implementation: grib_precision
*
* Description: how to control decimal precision when packing fields.
*
*/
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <assert.h>
#include "eccodes.h"
#define EPSILON 1e-6
#define EXPECTED_MIN 270.466796875
#define EXPECTED_MAX 311.096796875
int main(int argc, char** argv)
{
int err = 0;
size_t size=0;
FILE* in = NULL;
const char* infile = "../../data/regular_latlon_surface.grib1";
FILE* out = NULL;
const char* outfile = "out.precision.grib1";
codes_handle *h = NULL;
const void* buffer = NULL;
double* values1=NULL;
double* values2=NULL;
double maxa=0;
double maxv=0,minv=0;
double maxr=0,r=0;
long decimalPrecision;
long bitsPerValue1=0, bitsPerValue2=0;
int i=0;
in = fopen(infile,"r");
if(!in) {
printf("ERROR: unable to open input file %s\n",infile);
return 1;
}
out = fopen(outfile,"w");
if(!out) {
printf("ERROR: unable to open output file %s\n",outfile);
fclose(in);
return 1;
}
/* create a new handle from a message in a file */
h = codes_handle_new_from_file(0, in, PRODUCT_GRIB, &err);
if (h == NULL) {
printf("Error: unable to create handle from file %s\n",infile);
}
/* bitsPerValue before changing the packing parameters */
CODES_CHECK(codes_get_long(h,"bitsPerValue",&bitsPerValue1),0);
assert(bitsPerValue1 == 16);
/* get the size of the values array*/
CODES_CHECK(codes_get_size(h,"values",&size),0);
assert(size == 496);
values1 = (double*)malloc(size*sizeof(double));
/* get data values before changing the packing parameters*/
CODES_CHECK(codes_get_double_array(h,"values",values1,&size),0);
/* changing decimal precision to 2 means that 2 decimal digits
are preserved when packing. */
decimalPrecision=2;
CODES_CHECK(codes_set_long(h,"changeDecimalPrecision",decimalPrecision),0);
/* bitsPerValue after changing the packing parameters */
CODES_CHECK(codes_get_long(h,"bitsPerValue",&bitsPerValue2),0);
assert(bitsPerValue2 == 12);
values2 = (double*)malloc(size*sizeof(double));
/* get data values after changing the packing parameters*/
CODES_CHECK(codes_get_double_array(h,"values",values2,&size),0);
/* computing error */
maxa=0;
maxr=0;
maxv=values2[0];
minv=maxv;
for (i=0;i<size;i++) {
double a=fabs(values2[i]-values1[i]);
if ( values2[i] > maxv ) maxv=values2[i];
if ( values2[i] < minv ) minv=values2[i];
if ( values2[i] !=0 ) r=fabs((values2[i]-values1[i])/values2[i]);
if ( a > maxa ) maxa=a;
if ( r > maxr ) maxr=r;
}
printf("max absolute error = %g\n",maxa);
printf("max relative error = %g\n",maxr);
printf("min value = %g\n",minv);
printf("max value = %g\n",maxv);
assert(fabs(minv - EXPECTED_MIN) < EPSILON);
assert(fabs(maxv - EXPECTED_MAX) < EPSILON);
/* get the coded message in a buffer */
CODES_CHECK(codes_get_message(h,&buffer,&size),0);
/* write the buffer in a file*/
if(fwrite(buffer,1,size,out) != size)
{
perror(argv[1]);
exit(1);
}
codes_handle_delete(h);
fclose(in);
fclose(out);
return 0;
}
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