GPS.js

/* Copyright (c) 2013 Gordon Williams, Pur3 Ltd. See the file LICENSE for copying permission. */
/*
Module for interfacing with serial (NMEA) GPS devices

```
Serial4.setup(9600,{tx:C10,rx:C11});
var gps = connect(Serial4, function(data) {
  console.log(data);
});
```
*/
function handleGPSLine(line, callback) {
  var tag = line.substr(3,3);
  if (tag=="GGA") {
    var d = line.split(",");
    var dlat = d[2].indexOf(".");
    var dlon = d[4].indexOf(".");
    callback({
      time : d[1].substr(0,2)+":"+d[1].substr(2,2)+":"+d[1].substr(4,2),
      lat : (parseInt(d[2].substr(0,dlat-2),10)+parseFloat(d[2].substr(dlat-2))/60)*(d[3]=="S"?-1:1),
      lon : (parseInt(d[4].substr(0,dlon-2),10)+parseFloat(d[4].substr(dlon-2))/60)*(d[5]=="W"?-1:1),
      fix : parseInt(d[6],10),
      satellites : parseInt(d[7],10),
      altitude : parseFloat(d[9])
    });
  }
}


exports.connect = function(serial, callback) {
  var gps = {line:""};
  serial.on('data', function(data) {
    gps.line += data;
    var idx = gps.line.indexOf("\n");
    while (idx>=0) {
      var line = gps.line.substr(0, idx);
      gps.line = gps.line.substr(idx+1);
      handleGPSLine(line, callback); 
      idx = gps.line.indexOf("\n");     
    }
    if (gps.line.length > 80)
      gps.line = gps.line.substr(-80);
  });
  return gps;
}