File content as of revision 1:c266b90b4c74:

/* GPSINT.cpp
 * jbradshaw (20141101)
 * GPS functions are work of Tyler Weavers mbed gps library page 
 * (http://mbed.org/users/tylerjw/code/GPS/file/39d75e44b214/GPS.cpp)
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

#include "GPSINT.h"

GPSINT::GPSINT(PinName tx, PinName rx) : _gps(tx, rx) {
    _gps.baud(4800);
    GPSidx=0;          // Index for GPS buffer
    GPSstate=0;        // Used to wait for '$' in GPS interrupt
    _gps.attach(this,&GPSINT::GPSSerialRecvInterrupt, _gps.RxIrq);    // Recv interrupt handler
}

int GPSINT::nmea_validate(char *nmeastr){
    char check[3];
    char checkcalcstr[3];
    int i;
    int calculated_check;

    i=0;
    calculated_check=0;

    // check to ensure that the string starts with a $
    if(nmeastr[i] == '$')
        i++;
    else
        return 0;

    //No NULL reached, 75 char largest possible NMEA message, no '*' reached
    while((nmeastr[i] != 0) && (nmeastr[i] != '*') && (i < 75)){
        calculated_check ^= nmeastr[i];// calculate the checksum
        i++;
    }

    if(i >= 75){
        return 0;// the string was too long so return an error
    }

    if (nmeastr[i] == '*'){
        check[0] = nmeastr[i+1];    //put hex chars in check string
        check[1] = nmeastr[i+2];
        check[2] = 0;
    }
    else
        return 0;// no checksum separator found therefor invalid

    sprintf(checkcalcstr,"%02X",calculated_check);
    return((checkcalcstr[0] == check[0])
        && (checkcalcstr[1] == check[1])) ? 1 : 0 ;
} 

void GPSINT::parseGPSString(char *GPSstrParse){
    //check if $GPGGA string
    if(!strncmp(GPSstrParse, "$GPGGA", 6)){
        if (sscanf(GPSstrParse, "$GPGGA,%f,%f,%c,%f,%c,%d,%d,%f,%f,%c", &utc_time, &nmea_latitude, &ns, &nmea_longitude, &ew, &lock, &satelites, &hdop, &msl_altitude, &msl_units) >= 1) {
//            printf("%s", GPSstrParse);
            return;
        }
        else{
 //           printf("BAD parse %s", GPSstrParse);    
        }
    }
    // Check if $GPRMC string
    else if (!strncmp(GPSstrParse, "$GPRMC", 6)){
        if(sscanf(GPSstrParse, "$GPRMC,%f,%f,%c,%f,%c,%f,%f,%d", &utc_time, &nmea_latitude, &ns, &nmea_longitude, &ew, &speed_k, &course_d, &date) >= 1) {
//            printf("%s", GPSstrParse);
            return;
        }
        else{
 //           printf("BAD parse %s", GPSstrParse);    
        }
    }
    // GLL - Geographic Position-Lat/Lon
    else if (!strncmp(GPSstrParse, "$GPGLL", 6)){
        if(sscanf(GPSstrParse, "$GPGLL,%f,%c,%f,%c,%f,%c", &nmea_latitude, &ns, &nmea_longitude, &ew, &utc_time, &gll_status) >= 1) {
//            printf("%s", GPSstrParse);
            return;
        }
        else{
 //           printf("BAD parse %s", GPSstrParse);    
        }        
    }
    // VTG-Course Over Ground and Ground Speed
    else if (!strncmp(GPSstrParse, "$GPVTG", 6)){
        if(sscanf(GPSstrParse, "$GPVTG,%f,%c,%f,%c,%f,%c,%f,%c", &course_t, &course_t_unit, &course_m, &course_m_unit, &speed_k, &speed_k_unit, &speed_km, &speed_km_unit) >= 1) {
//            printf("%s", GPSstrParse);
            return;
        }
        else{
//            printf("BAD parse %s", GPSstrParse);    
        }        
    }            
}//parseGPSstring()

void GPSINT::GPSSerialRecvInterrupt(void)
{
    char c;
    c =_gps.getc();            // On receive interrupt, get the character.          
    //    pc.printf("%c", c);
    
    switch(GPSstate){
        case 0:
            if(c =='$'){
                GPSidx=0;
                Temp_GPSbuf[GPSidx] = c;  //load char in current idx of array
                GPSidx++;
                GPSstate = 1;
            }            
            break;
        case 1:                    
            Temp_GPSbuf[GPSidx] = c;  //load char in current idx of array
            GPSidx++;            
            if(c == '\n'){  //if last char was a newline
                Temp_GPSbuf[GPSidx] = '\0'; //append a NULL
                strcpy(GPSbuf, Temp_GPSbuf);    //copy temp buf into GPS buf
                GPSidx=0;                       //reset index
                GPSstate = 0;                   //reset GPS state
                if(nmea_validate(GPSbuf)){
                    parseGPSString(GPSbuf);
                }
            }            
            break;
        
        default:
            break;
            
    }//switch state                                 
}
     
float GPSINT::nmea_to_dec(float deg_coord, char nsew) {
    int degree = (int)(deg_coord/100);
    float minutes = deg_coord - degree*100;
    float dec_deg = minutes / 60;
    float decimal = degree + dec_deg;
    if (nsew == 'S' || nsew == 'W') { // return negative
        decimal *= -1;
    }
    return decimal;
}

// NAVIGATION FUNCTIONS ////////////////////////////////////////////////////////////
float GPSINT::calc_course_to(float pointLat, float pontLong) {
    const double d2r = PI / 180.0;
    const double r2d = 180.0 / PI;
    double dlat = abs(pointLat - dec_latitude) * d2r;
    double dlong = abs(pontLong - dec_longitude) * d2r;
    double y = sin(dlong) * cos(pointLat * d2r);
    double x = cos(dec_latitude*d2r)*sin(pointLat*d2r) - sin(dec_latitude*d2r)*cos(pointLat*d2r)*cos(dlong);
    return atan2(y,x)*r2d;
}    
 
/*
var y = Math.sin(dLon) * Math.cos(lat2);
var x = Math.cos(lat1)*Math.sin(lat2) -
        Math.sin(lat1)*Math.cos(lat2)*Math.cos(dLon);
var brng = Math.atan2(y, x).toDeg();
*/
 
/*
            The Haversine formula according to Dr. Math.
            http://mathforum.org/library/drmath/view/51879.html
                
            dlon = lon2 - lon1
            dlat = lat2 - lat1
            a = (sin(dlat/2))^2 + cos(lat1) * cos(lat2) * (sin(dlon/2))^2
            c = 2 * atan2(sqrt(a), sqrt(1-a)) 
            d = R * c
                
            Where
                * dlon is the change in longitude
                * dlat is the change in latitude
                * c is the great circle distance in Radians.
                * R is the radius of a spherical Earth.
                * The locations of the two points in 
                    spherical coordinates (longitude and 
                    latitude) are lon1,lat1 and lon2, lat2.
*/
double GPSINT::calc_dist_to_mi(float pointLat, float pontLong) {
    const double d2r = PI / 180.0;
    double dlat = pointLat - dec_latitude;
    double dlong = pontLong - dec_longitude;
    double a = pow(sin(dlat/2.0),2.0) + cos(dec_latitude*d2r) * cos(pointLat*d2r) * pow(sin(dlong/2.0),2.0);
    double c = 2.0 * asin(sqrt(abs(a)));
    double d = 63.765 * c;
    
    return d;
}
 
double GPSINT::calc_dist_to_ft(float pointLat, float pontLong) {
    return calc_dist_to_mi(pointLat, pontLong)*5280.0;
}
 
double GPSINT::calc_dist_to_km(float pointLat, float pontLong) {
    return calc_dist_to_mi(pointLat, pontLong)*1.609344;
}
 
double GPSINT::calc_dist_to_m(float pointLat, float pontLong) {
    return calc_dist_to_mi(pointLat, pontLong)*1609.344;
}