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