mirror of https://github.com/ecmwf/eccodes.git
132 lines
3.9 KiB
C
132 lines
3.9 KiB
C
/*
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* (C) Copyright 2005- 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: grib_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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#include <stdio.h>
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#include <stdlib.h>
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#include <math.h>
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#include <assert.h>
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#include "eccodes.h"
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#define EPSILON 1e-6
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#define EXPECTED_MIN 270.466796875
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#define EXPECTED_MAX 311.096796875
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int main(int argc, char** argv)
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{
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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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const char* infile = "../../data/regular_latlon_surface.grib1";
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FILE* out = NULL;
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const char* outfile = "out.precision.grib1";
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codes_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;
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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, "rb");
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if (!in) {
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fprintf(stderr, "Error: unable to open input file %s\n", infile);
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return 1;
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}
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out = fopen(outfile, "wb");
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if (!out) {
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fprintf(stderr, "Error: unable to open output file %s\n", outfile);
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fclose(in);
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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 = codes_handle_new_from_file(0, in, PRODUCT_GRIB, &err);
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if (h == NULL) {
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fprintf(stderr, "Error: unable to create handle from file %s\n", infile);
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fclose(out);
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return 1;
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}
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/* bitsPerValue before changing the packing parameters */
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CODES_CHECK(codes_get_long(h, "bitsPerValue", &bitsPerValue1), 0);
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assert(bitsPerValue1 == 16);
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/* get the size of the values array*/
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CODES_CHECK(codes_get_size(h, "values", &size), 0);
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assert(size == 496);
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values1 = (double*)malloc(size * sizeof(double));
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/* get data values before changing the packing parameters*/
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CODES_CHECK(codes_get_double_array(h, "values", values1, &size), 0);
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/* changing decimal precision to 2 means that 2 decimal digits
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are preserved when packing. */
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decimalPrecision = 2;
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CODES_CHECK(codes_set_long(h, "changeDecimalPrecision", decimalPrecision), 0);
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/* bitsPerValue after changing the packing parameters */
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CODES_CHECK(codes_get_long(h, "bitsPerValue", &bitsPerValue2), 0);
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assert(bitsPerValue2 == 12);
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values2 = (double*)malloc(size * sizeof(double));
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/* get data values after changing the packing parameters*/
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CODES_CHECK(codes_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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double a = fabs(values2[i] - values1[i]);
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if (values2[i] > maxv) maxv = values2[i];
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if (values2[i] < minv) 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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assert(fabs(minv - EXPECTED_MIN) < EPSILON);
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assert(fabs(maxv - EXPECTED_MAX) < EPSILON);
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/* get the coded message in a buffer */
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CODES_CHECK(codes_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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perror(argv[1]);
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exit(1);
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}
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codes_handle_delete(h);
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fclose(in);
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fclose(out);
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free(values1);
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free(values2);
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return 0;
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}
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