eccodes/examples/C/bufr_read_temp.c

/*
 * (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: bufr_read_temp
 *
 * Description: how to read temperature significant levels from TEMP BUFR messages.
 */

/*
 * Please note that TEMP reports can be encoded in various ways in BUFR. Therefore the code
 * below might not work directly for other types of TEMP messages than the one used in the
 * example. It is advised to use bufr_dump to understand the structure of the messages.
 */

#include "eccodes.h"

static void free_memory(double* sigt_pres, double* sigt_geo, double* sigt_t, double* sigt_td)
{
    free(sigt_pres);
    free(sigt_geo);
    free(sigt_t);
    free(sigt_td);
}

int main(int argc, char* argv[])
{
    FILE* in = NULL;

    /* message handle. Required in all the ecCodes calls acting on a message.*/
    codes_handle* h = NULL;

    double *sigt_pres = NULL, *sigt_geo = NULL, *sigt_t = NULL;
    double* sigt_td = NULL;
    size_t sigt_len = 0, len = 0, i = 0;
    int err            = 0;
    int cnt            = 0;
    const char* infile = "../../data/bufr/temp_101.bufr";
    char key_name[128];

    in = fopen(infile, "rb");
    if (!in) {
        fprintf(stderr, "Error: unable to open file %s\n", infile);
        return 1;
    }

    /* loop over the messages in the BUFR file */
    while ((h = codes_handle_new_from_file(NULL, in, PRODUCT_BUFR, &err)) != NULL || err != CODES_SUCCESS) {
        if (h == NULL) {
            fprintf(stderr, "Error: unable to create handle for message %d\n", cnt);
            cnt++;
            continue;
        }

        printf("message: %d\n", cnt);

        /* we need to instruct ecCodes to expand the descriptors
           i.e., unpack the data values */
        CODES_CHECK(codes_set_long(h, "unpack", 1), 0);

        /* in what follows we rely on the fact that for
         * temperature significant levels the value of key
         * verticalSoundingSignificance is 4 (see flag table 8001 for details).
         *
         * In our BUFR message verticalSoundingSignificance is always followed by
         *    geopotential, airTemperature, dewpointTemperature,
         *    windDirection, windSpeed and pressure.
         * So in order to access any of these keys we need to use the
         * condition: verticalSoundingSignificance=4.
         */

        /* get the number of the temperature significant levels.*/

        /* we find out the number of temperature significant levels by
         * counting how many pressure values we have on these levels.*/

        snprintf(key_name, sizeof(key_name), "/verticalSoundingSignificance=4/pressure");
        CODES_CHECK(codes_get_size(h, key_name, &sigt_len), 0);

        printf("Number of T significant levels: %zu\n", sigt_len);

        /* allocate memory for the values to be read. Each
         * parameter must have the same number of values. */
        sigt_pres = (double*)malloc(sigt_len * sizeof(double));
        sigt_geo  = (double*)malloc(sigt_len * sizeof(double));
        sigt_t    = (double*)malloc(sigt_len * sizeof(double));
        sigt_td   = (double*)malloc(sigt_len * sizeof(double));

        /* get pressure */
        snprintf(key_name, sizeof(key_name), "/verticalSoundingSignificance=4/pressure");
        len = sigt_len;
        CODES_CHECK(codes_get_double_array(h, key_name, sigt_pres, &len), 0);

        /* get geopotential */
        snprintf(key_name, sizeof(key_name), "/verticalSoundingSignificance=4/nonCoordinateGeopotential");

        /* check the size */
        CODES_CHECK(codes_get_size(h, key_name, &len), 0);
        if (len != sigt_len) {
            fprintf(stderr, "Error: inconsistent number of geopotential values found!\n");
            free_memory(sigt_pres, sigt_geo, sigt_t, sigt_td);
            return 1;
        }

        /* get the values */
        CODES_CHECK(codes_get_double_array(h, key_name, sigt_geo, &len), 0);

        /* get temperature */
        if (len != sigt_len) { /* check the size */
            fprintf(stderr, "Error: inconsistent number of temperature values found!\n");
            free_memory(sigt_pres, sigt_geo, sigt_t, sigt_td);
            return 1;
        }

        /* get the values */
        snprintf(key_name, sizeof(key_name), "/verticalSoundingSignificance=4/airTemperature");
        CODES_CHECK(codes_get_double_array(h, key_name, sigt_t, &len), 0);

        /* get dew point */
        if (len != sigt_len) { /* check the size */
            fprintf(stderr, "Error: inconsistent number of dewpoint temperature values found!\n");
            free_memory(sigt_pres, sigt_geo, sigt_t, sigt_td);
            return 1;
        }

        /* get the values */
        snprintf(key_name, sizeof(key_name), "/verticalSoundingSignificance=4/dewpointTemperature");
        CODES_CHECK(codes_get_double_array(h, key_name, sigt_td, &len), 0);

        /* print the values */
        printf("lev  pres    geo    t    td\n");
        printf("-------------------------------\n");

        for (i = 0; i < sigt_len; i++) {
            printf("%3lu %6.0f %6.0f %.1f %.1f\n",
                   (unsigned long)(i + 1), sigt_pres[i], sigt_geo[i], sigt_t[i], sigt_td[i]);
        }

        /* release memory */
        codes_handle_delete(h);
        free_memory(sigt_pres, sigt_geo, sigt_t, sigt_td);

        cnt++;
    }

    fclose(in);
    return 0;
}