eccodes/examples/C/grib_iterator_bitmap.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.
 */

/*
 * Description: How to use an iterator on lat/lon/values and query the bitmap
 *              for missing values
 *              (rather than compare each value with the missingValue key)
 */

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include "eccodes.h"

static void usage(const char* prog)
{
    printf("Usage: %s grib_file\n", prog);
    exit(1);
}

int main(int argc, char** argv)
{
    FILE* in = NULL;
    int err  = 0;
    double lat, lon, value;
    int n          = 0;
    size_t bmp_len = 0, values_len = 0;
    char* filename       = NULL;
    long bitmapPresent   = 0;
    long* bitmap         = NULL;
    double* values       = NULL;
    codes_handle* h      = NULL;
    codes_iterator* iter = NULL;

    if (argc != 2) usage(argv[0]);
    filename = argv[1];
    in       = fopen(filename, "rb");
    if (!in) {
        fprintf(stderr, "ERROR: unable to open file %s\n", filename);
        return 1;
    }

    while ((h = codes_handle_new_from_file(0, in, PRODUCT_GRIB, &err)) != NULL) {
        if (err != CODES_SUCCESS) CODES_CHECK(err, 0);

        CODES_CHECK(codes_get_long(h, "bitmapPresent", &bitmapPresent), 0);
        if (bitmapPresent) {
            CODES_CHECK(codes_get_size(h, "bitmap", &bmp_len), 0);
            bitmap = (long*)malloc(bmp_len * sizeof(long));
            CODES_CHECK(codes_get_long_array(h, "bitmap", bitmap, &bmp_len), 0);
            printf("Bitmap is present. Num = %zu\n", bmp_len);
        }
        /* sanity check. Number of values must match number in bitmap */
        CODES_CHECK(codes_get_size(h, "values", &values_len), 0);
        values = (double*)malloc(values_len * sizeof(double));
        CODES_CHECK(codes_get_double_array(h, "values", values, &values_len), 0);
        if (bitmapPresent) {
            assert(values_len == bmp_len);
        }

        /* a new iterator on lat/lon/values is created from the message handle h */
        iter = codes_grib_iterator_new(h, 0, &err);
        if (err != CODES_SUCCESS) CODES_CHECK(err, 0);

        n = 0;
        /* loop on all the lat/lon/values. Only print non-missing values */
        while (codes_grib_iterator_next(iter, &lat, &lon, &value)) {
            /* consult bitmap to see if the n'th value is missing */
            int is_missing_val = (bitmapPresent && bitmap[n] == 0);
            if (!is_missing_val) {
                printf("- %d - lat=%f lon=%f value=%f\n", n, lat, lon, value);
            }
            n++;
        }
        /* check number of elements in iterator matches value count */
        assert(n == values_len);

        codes_grib_iterator_delete(iter);
        codes_handle_delete(h);
    }

    fclose(in);
    return 0;
}