GPS.cpp

00001 /* mbed EM-406 GPS Module Library
00002  * Copyright (c) 2008-2010, sford
00003  *
00004  * Permission is hereby granted, free of charge, to any person obtaining a copy
00005  * of this software and associated documentation files (the "Software"), to deal
00006  * in the Software without restriction, including without limitation the rights
00007  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
00008  * copies of the Software, and to permit persons to whom the Software is
00009  * furnished to do so, subject to the following conditions:
00010  *
00011  * The above copyright notice and this permission notice shall be included in
00012  * all copies or substantial portions of the Software.
00013  *
00014  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
00015  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
00016  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
00017  * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
00018  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
00019  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
00020  * THE SOFTWARE.
00021  */
00022  
00023 #include "GPS.h"
00024 
00025 GPS::GPS(PinName tx, PinName rx) : _gps(tx, rx) {
00026     _gps.baud(4800);    
00027     longitude = 0.0;
00028     latitude = 0.0;        
00029 }
00030 
00031 int GPS::sample() {
00032     float time, hdop;
00033     char ns, ew;
00034     int lock;
00035 
00036     while(1) {        
00037         getline();
00038         
00039         printf("MSG: %s\r\n", msg);
00040 
00041         // Check if it is a GPGGA msg (matches both locked and non-locked msg)
00042         if(sscanf(msg, "GPGGA,%f,%f,%c,%f,%c,%d,%d,%f,%f", &time, &latitude, &ns, &longitude, &ew, &lock, &satellites, &hdop, &altitude) >= 1) {
00043             
00044             printf("LOCK: %d\r\n", lock);
00045              
00046             if(lock == 1 || lock == 2 || lock == 6) { // GPS or Differential GPS or Dead Reckoning Fix
00047                 float degrees = trunc(latitude / 100.0f);
00048                 float minutes = latitude - (degrees * 100.0f);
00049                 latitude = degrees + minutes / 60.0f;    
00050                 
00051                 degrees = trunc(longitude / 100.0f);
00052                 minutes = longitude - (degrees * 100.0f);
00053                 longitude = degrees + minutes / 60.0f;
00054                 
00055                 if(ns == 'S') { latitude  *= -1.0; }
00056                 if(ew == 'W') { longitude *= -1.0; }
00057                 
00058                 return 1;
00059             } else {
00060                 longitude = 0.0;
00061                 latitude = 0.0;  
00062                 altitude = 0.0;      
00063                 return 0;
00064             }   
00065         }
00066     }
00067 }
00068 
00069 float GPS::trunc(float v) {
00070     if(v < 0.0) {
00071         v*= -1.0;
00072         v = floor(v);
00073         v*=-1.0;
00074     } else {
00075         v = floor(v);
00076     }
00077     return v;
00078 }
00079 
00080 void GPS::getline() {
00081     while(_gps.getc() != '$');    // wait for the start of a line
00082     for(int i=0; i<256; i++) {
00083         msg[i] = _gps.getc();
00084         if(msg[i] == '\r') {
00085             msg[i] = 0;
00086             return;
00087         }
00088     }
00089     error("Overflowed message limit");
00090 }