nmea.c

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#include <config.h>

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

#include <cartcomm/nmea.h>
#include "nan.h"


double nmea_to_deg(char *nmea) {
    int b;
    char min[8] = {0};
    double dmin;
    char deg[5] = {0};
    int ideg;
    double ddeg;

    // Position of the first minute digit (zero-based)
    // in the nmea string
    b = strlen(nmea) - 8;

    if(b < 0)
        return NAN; // return NAN value on invalid input

    // Extract the minutes as a string, convert to decimal
    strncpy(min, nmea + b, sizeof(min));
    min[sizeof(min)-1] = '\0';
    dmin = strtod(min, NULL);

    // Extract the degrees as a string, convert to integer
    if(b > sizeof(deg))
        return (0.0/0.0);
    strncpy(deg, nmea, b);
    deg[sizeof(deg)-1] = '\0';
    ideg = atoi(deg);

    // Combine degrees and minutes into decimal degrees
    ddeg = abs(ideg) + dmin / 60.0; // add absolute values
    if(ideg < 0)
        ddeg = -ddeg;   // assign the sign of the degrees

    return ddeg;
}


void deg_to_nmea(double ddeg, char *nmea, int nmeasize) {
    int ideg;
    double dmin;

    // Get the whole degrees as integer
    ideg = (int) abs(ddeg);
    if(ddeg < 0.0)
        ideg = -ideg;

    // Convert the remaining fractional degrees into minutes
    dmin = 60.0 * fabs(ddeg - ideg);

    // Write out the NMEA-formatted string
    snprintf(nmea, nmeasize, "%d%08.5f", ideg, dmin);
}

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