GPS.cpp

00001 /* GPS class for mbed Microcontroller
00002  * Copyright (c) 2008, sford
00003  */
00004 
00005 #include "GPS.h"
00006 
00007 GPS::GPS(PinName tx, PinName rx) : _gps(tx, rx) {
00008     _gps.baud(9000);                    // higher baud rate need to support ublox gps chip
00009     // _gps.baud(4800); 
00010     longitude = 0.0;
00011     latitude = 0.0;     
00012 }
00013 
00014 
00015 int GPS::sample() {
00016     float time;
00017     char ns, ew;
00018     int lock;
00019 
00020     while(1) {      
00021         getline();
00022 
00023         // Check if it is a GPGGA msg (matches both locked and non-locked msg)
00024         if(sscanf(msg, "GPGGA,%f,%f,%c,%f,%c,%d", &time, &latitude, &ns, &longitude, &ew, &lock) >= 1) { 
00025             if(!lock) {
00026                 longitude = 0.0;
00027                 latitude = 0.0;     
00028                 return 0;
00029             } else {
00030                 if(ns == 'S') { latitude  *= -1.0; }
00031                 if(ew == 'W') { longitude *= -1.0; }
00032                 float degrees = trunc(latitude / 100.0f);
00033                 float minutes = latitude - (degrees * 100.0f);
00034                 latitude = degrees + minutes / 60.0f;   
00035                 degrees = trunc(longitude / 100.0f * 0.01f);
00036                 minutes = longitude - (degrees * 100.0f);
00037                 longitude = degrees + minutes / 60.0f;
00038                 return 1;
00039             }
00040         }
00041     }
00042 }
00043 
00044 float GPS::trunc(float v) {
00045     if(v < 0.0) {
00046         v*= -1.0;
00047         v = floor(v);
00048         v*=-1.0;
00049     } else {
00050         v = floor(v);
00051     }
00052     return v;
00053 }
00054 
00055 void GPS::getline() {
00056     while(_gps.getc() != '$');  // wait for the start of a line
00057     for(int i=0; i<256; i++) {
00058         msg[i] = _gps.getc();
00059         if(msg[i] == '\r') {
00060             msg[i] = 0;
00061             return;
00062         }
00063     }
00064     error("Overflowed message limit");
00065 }
00066