dejwoo/GPS.js

A GPS NMEA parser library

GPS.js is an extensible parser for NMEA sentences, given by any common GPS receiver. The output is tried to be as high-level as possible to make it more useful than simply splitting the information. The aim is, that you don't have to understand NMEA, just plug in your receiver and you're ready to go.

Usage

The interface of GPS.js is as simple as the following few lines. You need to add an event-listener for the completion of the task and invoke the update method with a sentence you want to process. There are much more examples in the examples folder.

var gps = new GPS;

// Add an event listener on all protocols
gps.on('data', function(raw, parsed) {
    
    console.log(parsed);
});

// Call the update routine directly with a NMEA sentence, which would
// come from the serial port or stream-reader normally
gps.update("$GPGGA,224900.000,4832.3762,N,00903.5393,E,1,04,7.8,498.6,M,48.0,M,,0000*5E");

It's also possible to add event-listeners only on one of the following protocols, by stating gps.on('GGA', ...) for example.

State

The real advantage over other NMEA implementations is, that the GPS information is interpreted and normalized. The most high-level API is the state object, which changes with every new event. You can use this information with:

gps.on('data', function(raw, data) {
  console.log(gps.state);
});

Installation

Installing GPS.js is as easy as cloning this repo or use the following command:

npm install --save gps

Examples

GPS.js comes with some examples, like drawing the current latutude and longitude to Google Maps, displaying a persistent state and displaying the parsed raw data. In some cases you have to adjust the serial path to your own GPS receiver to make it work.

Simple serial example

var SerialPort = require('serialport');
var port = new SerialPort.SerialPort('/dev/tty.usbserial', { // change path
  baudrate: 4800,
  parser: SerialPort.parsers.readline('\r\n')
});

var GPS = require('gps');
var gps = new GPS;

gps.on('data', function(data) {
  console.log(data, gps.state);
});

port.on('data', function(data) {
  gps.update(data);
});

Dashboard

Go into the folder examples/dashboard and start the server with

node server

After that you can open the browser and go to http://localhost:3000 The result should look like

Google Maps

Go into the folder examples/maps and start the server with

node server

After that you can open the browser and go to http://localhost:3000 The result should look like

Available Methods

update(line)

The update method is the most important function, it adds a new NMEA sentence and forces the callback to trigger

updatePartial(chunk)

Will call update() when a full NMEA sentence has been arrived

on(event, callback)

Adds an event listener for a protocol to occur (see implemented protocols, simply use the name - upper case) or for all sentences with data. Because GPS.js should be more general, it doesn't inherit EventEmitter, but simply invokes the callback.

off(event)

Removes an event listener

Implemented Protocols

GGA - Fix information

Gets the data, you're most probably looking for: latitude and longitude

The parsed object will have the following attributes:

• type: "GGA"
• time: The time given as a JavaScript Date object
• lat: The latitude
• lon: The longitude
• alt: The altitude
• quality: Fix quality (either invalid, fix or diff)
• satelites: Number of satellites being tracked
• hdop: Horizontal dilution of precision
• geoidal: Height of geoid (mean sea level)
• age: time in seconds since last DGPS update
• stationID: DGPS station ID number
• valid: Indicates if the checksum is okay

RMC - NMEAs own version of essential GPS data

Similar to GGA but gives also delivers the velocity

The parsed object will have the following attributes:

• type: "RMC"
• time: The time given as a JavaScript Date object
• status: Status active or void
• lat: The latitude
• lon: The longitude
• speed: Speed over the ground in km/h
• track: Track angle in degrees
• variation: Magnetic Variation
• faa: The FAA mode, introduced with NMEA 2.3
• valid: Indicates if the checksum is okay

GSA - Active satellites

The parsed object will have the following attributes:

• type: "GSA"
• mode: Auto selection of 2D or 3D fix (either auto or manual)
• fix: The selected fix mode (either 2D or 3D)
• satellites: Array of satellite IDs
• pdop: Position dilution of precision
• vdop: Vertical dilution of precision
• hdop: Horizontal dilution of precision
• valid: Indicates if the checksum is okay

GLL - Geographic Position - Latitude/Longitude

The parsed object will have the following attributes:

• type: "GLL"
• lat: The latitude
• lon: The longitude
• status: Status active or void
• time: The time given as a JavaScript Date object
• valid: Indicates if the checksum is okay

GSV - List of Satellites in view

GSV messages are paginated. msgNumber indicates the current page and msgsTotal is the total number of pages.

The parsed object will have the following attributes:

• type: "GSV"
• msgNumber: Current page
• msgsTotal: Number of pages
• satellites: Array of satellite objects with the following attributes:
  • prn: Satellite PRN number
  • elevation: Elevation in degrees
  • azimuth: Azimuth in degrees
  • snr: Signal to Noise Ratio (higher is better)
• valid: Indicates if the checksum is okay

VTG - vector track and speed over ground

The parsed object will have the following attributes:

• type: "VTG"
• track: Track in degrees
• speed: Speed over ground in km/h
• faa: The FAA mode, introduced with NMEA 2.3
• valid: Indicates if the checksum is okay

ZDA - UTC day, month, and year, and local time zone offset

The parsed object will have the following attributes:

• type: "ZDA"
• time: The time given as a JavaScript Date object

GPS State

If the streaming API is not needed, but a solid state of the system, the gps.state object can be used. It has the following properties:

• time: Current time
• lat: Latitude
• lon: Longitude
• alt: Altitude
• sats_active: Array of active satellites
• speed: Speed over ground in km/h
• track: Track in degrees
• sats_visible: Array of all visible satellites

Adding new protocols is a matter of minutes. If you need a protocol which isn't implemented, I'm happy to see a pull request or a new ticket.

Functions

GPS.js comes with a few static functions, which help by working with geo-coordinates.

GPS.Parse(line)

Parses a single line and returns the resulting object, in case the callback system isn't needed/wanted

GPS.Distance(latFrom, lonFrom, latTo, lonTo)

Calculates the distance between two geo-coordinates using Haversine formula

GPS.Bearing(latFrom, lonFrom, latTo, lonTo)

Calculates the angle from one coordinate to another

Using GPS.js with the browser

The use cases should be rare to parse NMEA directly inside the browser, but it works too.

<script src="gps.js"></script>
<script>
   var gps = new GPS;
   gps.update('...');
</script>

Testing

If you plan to enhance the library, make sure you add test cases and all the previous tests are passing. You can test the library with

npm test

Copyright and licensing

Copyright (c) 2016, Robert Eisele (robert@xarg.org) Dual licensed under the MIT or GPL Version 2 licenses.