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;
00033     char ns, ew;
00034     int lock;
00035 
00036     while(1) {        
00037         getline();
00038 
00039         // Check if it is a GPGGA msg (matches both locked and non-locked msg)
00040         if(sscanf(msg, "GPGGA,%f,%f,%c,%f,%c,%d", &time, &latitude, &ns, &longitude, &ew, &lock) >= 1) { 
00041             if(!lock) {
00042                 longitude = 0.0;
00043                 latitude = 0.0;        
00044                 return 0;
00045             } else {
00046                 if(ns == 'S') {    latitude  *= -1.0; }
00047                 if(ew == 'W') {    longitude *= -1.0; }
00048                 float degrees = trunc(latitude / 100.0f);
00049                 float minutes = latitude - (degrees * 100.0f);
00050                 latitude = degrees + minutes / 60.0f;    
00051                 degrees = trunc(longitude / 100.0f);
00052                 minutes = longitude - (degrees * 100.0f);
00053                 longitude = degrees + minutes / 60.0f;
00054                 rtime = time;
00055                 return 1;
00056             }
00057         }
00058     }
00059 }
00060 
00061 float GPS::trunc(float v) {
00062     if(v < 0.0) {
00063         v*= -1.0;
00064         v = floor(v);
00065         v*=-1.0;
00066     } else {
00067         v = floor(v);
00068     }
00069     return v;
00070 }
00071 
00072 void GPS::getline() {
00073     while(_gps.getc() != '$');    // wait for the start of a line
00074     for(int i=0; i<256; i++) {
00075         msg[i] = _gps.getc();
00076         if(msg[i] == '\r') {
00077             msg[i] = 0;
00078             return;
00079         }
00080     }
00081     error("Overflowed message limit");
00082 }