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Description

This example shows: 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)

Source code

grib_iterator_bitmap.py
#
# Copyright 2005-2018 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)
#
from __future__ import print_function
import traceback
import sys

from eccodes import *

VERBOSE = 1  # verbose error reporting


def example(INPUT):
    f = open(INPUT, 'rb')

    while 1:
        gid = codes_grib_new_from_file(f)
        if gid is None:
            break

        iterid = codes_grib_iterator_new(gid, 0)

        bitmapPresent = codes_get(gid, 'bitmapPresent')
        if bitmapPresent:
            # Get the bitmap array which contains 0s and 1s
            bitmap = codes_get_array(gid, 'bitmap', int)
            # Do some sanity checking
            assert len(bitmap) == codes_get_size(gid, 'values')
            assert len(bitmap) == codes_get(gid, 'numberOfDataPoints')

        i = 0
        while 1:
            result = codes_grib_iterator_next(iterid)
            if not result:
                break

            [lat, lon, value] = result

            sys.stdout.write("- %d - lat=%.6e lon=%.6e value=" % (i, lat, lon))

            # Consult bitmap to see if the i'th value is missing
            if bitmapPresent and bitmap[i] == 0:
                print("missing")
            else:
                print("%.6f" % value)

            i += 1

        codes_grib_iterator_delete(iterid)
        codes_release(gid)

    f.close()


def main():
    try:
        example(sys.argv[1])
    except CodesInternalError as err:
        if VERBOSE:
            traceback.print_exc(file=sys.stderr)
        else:
            sys.stderr.write(err.msg + '\n')

        return 1


if __name__ == "__main__":
    sys.exit(main())
grib_iterator_bitmap.c
/*
 * Copyright 2005-2018 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 <string.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,"r");
    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 = %lu\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;
}
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