mirror of https://github.com/ecmwf/eccodes.git
125 lines
3.2 KiB
C
125 lines
3.2 KiB
C
/*
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* Copyright 2005-2014 ECMWF.
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*
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* This software is licensed under the terms of the Apache Licence Version 2.0
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* which can be obtained at http://www.apache.org/licenses/LICENSE-2.0.
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*
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* In applying this licence, ECMWF does not waive the privileges and immunities granted to it by
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* virtue of its status as an intergovernmental organisation nor does it submit to any jurisdiction.
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*/
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/*
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* C Implementation: precision
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*
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* Description: how to control decimal precision when packing fields.
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*
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*
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*
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*
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <math.h>
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#include "grib_api.h"
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int main(int argc, char** argv) {
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int err = 0;
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size_t size=0;
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FILE* in = NULL;
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char* infile = "../data/regular_latlon_surface.grib1";
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FILE* out = NULL;
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char* outfile = "out.grib1";
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grib_handle *h = NULL;
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const void* buffer = NULL;
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double* values1=NULL;
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double* values2=NULL;
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double maxa=0,a=0;
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double maxv=0,minv=0;
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double maxr=0,r=0;
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long decimalPrecision;
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long bitsPerValue1=0, bitsPerValue2=0;
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int i=0;
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in = fopen(infile,"r");
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if(!in) {
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printf("ERROR: unable to open file %s\n",infile);
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return 1;
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}
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out = fopen(outfile,"w");
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if(!in) {
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printf("ERROR: unable to open file %s\n",outfile);
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return 1;
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}
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/* create a new handle from a message in a file */
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h = grib_handle_new_from_file(0,in,&err);
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if (h == NULL) {
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printf("Error: unable to create handle from file %s\n",infile);
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}
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/* bitsPerValue before changing the packing parameters */
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GRIB_CHECK(grib_get_long(h,"bitsPerValue",&bitsPerValue1),0);
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/* get the size of the values array*/
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GRIB_CHECK(grib_get_size(h,"values",&size),0);
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values1 = malloc(size*sizeof(double));
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/* get data values before changing the packing parameters*/
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GRIB_CHECK(grib_get_double_array(h,"values",values1,&size),0);
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/* setting decimal precision=2 means that 2 decimal digits
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are preserved when packing. */
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decimalPrecision=2;
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GRIB_CHECK(grib_set_long(h,"setDecimalPrecision",decimalPrecision),0);
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/* bitsPerValue after changing the packing parameters */
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GRIB_CHECK(grib_get_long(h,"bitsPerValue",&bitsPerValue2),0);
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values2 = malloc(size*sizeof(double));
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/* get data values after changing the packing parameters*/
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GRIB_CHECK(grib_get_double_array(h,"values",values2,&size),0);
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/* computing error */
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maxa=0;
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maxr=0;
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maxv=values2[0];
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minv=maxv;
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for (i=0;i<size;i++) {
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a=fabs(values2[i]-values1[i]);
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if ( values2[i] > maxv ) maxv=values2[i];
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if ( values2[i] < maxv ) minv=values2[i];
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if ( values2[i] !=0 ) r=fabs((values2[i]-values1[i])/values2[i]);
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if ( a > maxa ) maxa=a;
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if ( r > maxr ) maxr=r;
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}
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printf("max absolute error = %g\n",maxa);
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printf("max relative error = %g\n",maxr);
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printf("min value = %g\n",minv);
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printf("max value = %g\n",maxv);
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printf("old number of bits per value=%ld\n",(long)bitsPerValue1);
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printf("new number of bits per value=%ld\n",(long)bitsPerValue2);
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/* get the coded message in a buffer */
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GRIB_CHECK(grib_get_message(h,&buffer,&size),0);
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/* write the buffer in a file*/
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if(fwrite(buffer,1,size,out) != size)
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{
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perror(argv[1]);
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exit(1);
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}
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/* delete handle */
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grib_handle_delete(h);
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fclose(in);
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fclose(out);
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return 0;
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}
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