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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.
*/
/*
* C Implementation: precision
*
* Description: how to control decimal precision when packing fields.
*
*
*
*
*/
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include "grib_api.h"
int main(int argc, char** argv) {
int err = 0;
size_t size=0;
FILE* in = NULL;
char* infile = "../data/regular_latlon_surface.grib1";
FILE* out = NULL;
char* outfile = "out.grib1";
grib_handle *h = NULL;
const void* buffer = NULL;
double* values1=NULL;
double* values2=NULL;
double maxa=0,a=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 file %s\n",infile);
return 1;
}
out = fopen(outfile,"w");
if(!in) {
printf("ERROR: unable to open file %s\n",outfile);
return 1;
}
/* create a new handle from a message in a file */
h = grib_handle_new_from_file(0,in,&err);
if (h == NULL) {
printf("Error: unable to create handle from file %s\n",infile);
}
/* bitsPerValue before changing the packing parameters */
GRIB_CHECK(grib_get_long(h,"bitsPerValue",&bitsPerValue1),0);
/* get the size of the values array*/
GRIB_CHECK(grib_get_size(h,"values",&size),0);
values1 = malloc(size*sizeof(double));
/* get data values before changing the packing parameters*/
GRIB_CHECK(grib_get_double_array(h,"values",values1,&size),0);
/* setting decimal precision=2 means that 2 decimal digits
are preserved when packing. */
decimalPrecision=2;
GRIB_CHECK(grib_set_long(h,"setDecimalPrecision",decimalPrecision),0);
/* bitsPerValue after changing the packing parameters */
GRIB_CHECK(grib_get_long(h,"bitsPerValue",&bitsPerValue2),0);
values2 = malloc(size*sizeof(double));
/* get data values after changing the packing parameters*/
GRIB_CHECK(grib_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++) {
a=fabs(values2[i]-values1[i]);
if ( values2[i] > maxv ) maxv=values2[i];
if ( values2[i] < maxv ) 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);
printf("old number of bits per value=%ld\n",(long)bitsPerValue1);
printf("new number of bits per value=%ld\n",(long)bitsPerValue2);
/* get the coded message in a buffer */
GRIB_CHECK(grib_get_message(h,&buffer,&size),0);
/* write the buffer in a file*/
if(fwrite(buffer,1,size,out) != size)
{
perror(argv[1]);
exit(1);
}
/* delete handle */
grib_handle_delete(h);
fclose(in);
fclose(out);
return 0;
}
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