eccodes/examples/C/grib_nearest.c

/*
 * Copyright 2005-2019 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: nearest
 *
 * Description: How to get nearest point(s).
 *              Assumes all input GRIB messages have the same grid geometry
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "eccodes.h"

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

int main(int argc, char** argv)
{
    int err = 0;
    long step=0;
    size_t nfiles=0;
    size_t i=0, j=0;
    codes_fieldset* set=NULL;
    const size_t max_numfiles = 100;
    codes_handle* h=NULL;
    char param[20]={0,};
    size_t len=20;
    double lats[4]={0,};
    double lons[4]={0,};
    double values[4]={0,};
    double distances[4]={0,};
    int indexes[4]={0,};
    char* order_by="param,step";
    double* pValues = values; /* Default: decode the values */

    size_t size=4;
    double lat=-40,lon=15;
    int mode=0;
    int count;
    char** filenames;
    codes_nearest* nearest=NULL;

    if (argc < 2) usage(argv[0]);

    filenames=(char**)malloc(sizeof(char*)*max_numfiles);

    for(i=1; i<argc; ++i) {
        if (strcmp(argv[i],"-n")==0) {
            pValues = NULL; /* Do not decode the values */
        } else {
            if (j >= max_numfiles)
                break;
            filenames[j++]=(char*)strdup(argv[i]);
        }
    }
    nfiles = j;

    set=codes_fieldset_new_from_files(0,filenames,nfiles,0,0,0,order_by,&err);
    CODES_CHECK(err,0);

    printf("ordering by %s\n",order_by);
    printf("%d fields in the fieldset\n",codes_fieldset_count(set));
    printf("n,step,param\n");

    mode=CODES_NEAREST_SAME_GRID | CODES_NEAREST_SAME_POINT;
    count=1;

    while ((h=codes_fieldset_next_handle(set,&err))!=NULL) {
        CODES_CHECK(codes_get_long(h,"step",&step),0);
        len=20;
        CODES_CHECK(codes_get_string(h,"shortName",param,&len),0);

        printf("%d %ld %s  ",count,step,param);
        if (!nearest) nearest=codes_grib_nearest_new(h,&err);
        CODES_CHECK(err,0);
        CODES_CHECK(codes_grib_nearest_find(nearest,h,lat,lon,mode,lats,lons,pValues,distances,indexes,&size),0);
        if (!pValues) {
            printf("\nIdx\tlat\tlon\tdist\n");
            for (i=0;i<4;i++) printf("%d\t%.2f\t%.2f\t%g\n",
                    (int)indexes[i],lats[i],lons[i],distances[i]);
        } else {
            printf("\nIdx\tlat\tlon\tdist\tval\n");
            for (i=0;i<4;i++) printf("%d\t%.2f\t%.2f\t%g\t%g\n",
                    (int)indexes[i],lats[i],lons[i],distances[i],pValues[i]);
        }
        printf("\n");

        codes_handle_delete(h);
        count++;
    }

    if (nearest) codes_grib_nearest_delete(nearest);

    if (set) codes_fieldset_delete(set);

    return 0;
}