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(115200);    
00027     longitude = 0.0;
00028     latitude = 0.0;        
00029 }
00030 
00031 int GPS::sample() {
00032 
00033     char ns, ew;
00034         
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,%d", &time, &latitude, &ns, &longitude, &ew, &lock, &sate_in_view) >= 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                 return 1;
00055             }
00056         }
00057     }
00058 }
00059 
00060 float GPS::trunc(float v) {
00061     if(v < 0.0) {
00062         v*= -1.0;
00063         v = floor(v);
00064         v*=-1.0;
00065     } else {
00066         v = floor(v);
00067     }
00068     return v;
00069 }
00070 
00071 void GPS::getline() {
00072     while(_gps.getc() != '$');    // wait for the start of a line
00073     for(int i=0; i<256; i++) {
00074         msg[i] = _gps.getc();
00075         if(msg[i] == '\r') {
00076             msg[i] = 0;
00077             return;
00078         }
00079     }
00080     error("Overflowed message limit");
00081 }