A GPS NMEA parser library
npm install @iotek/gps
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.
``javascript
const gps = new GPS;
// Add an event listener on all protocols
gps.on('data', 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:
`javascript`
gps.on('data', () => {
console.log(gps.state);
});
Installation
===
Installing GPS.js is as easy as cloning this repo or use the following command:
`
npm install gps
Find the serial device
===
On Linux serial devices typically have names like /dev/ttyS1, on OSX /dev/tty.usbmodem1411 after installing a USB to serial driver and on Windows, you're probably fine by using the highest COM device you can find in the device manager. Please note that if you have multiple USB ports on your computer and use them randomly, you have to lookup the path/device again.
Register device on a BeagleBone
---
If you find yourself on a BeagleBone, the serial device must be registered manually. Luckily, this can be done within node quite easily using octalbonescript:
`javascript`
const obs = require('octalbonescript');
obs.serial.enable('/dev/ttyS1', () => {
console.log('serial device activated');
});
Examples
===
GPS.js comes with some examples, like drawing the current latitude 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
---
`javascript
const SerialPort = require('serialport');
const GPS = require('gps');
const port = new SerialPort('/dev/tty.usbmodem11401', { // change path
baudRate: 9600,
parser: new SerialPort.parsers.Readline({
delimiter: '\r\n'
})
});
const gps = new GPS;
gps.on('data', data => {
console.log(data, gps.state);
})
port.on('data', data => {
gps.updatePartial(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 the following, which in principle is just a visualization of the state object gps.state
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
Confluence
---
Confluence is a project, which tries to travel to and document all integer GPS coordinates. GPS.js can assist on that goal. Go into the examples folder and run:
`
node confluence
You should see something like the following, updating as you move around
`
You are at (48.53, 9.05951),
The closest confluence point (49, 9) is in 51.36 km.
You have to go 355.2° N
Set Time
---
On systems without a RTC - like Raspberry PI - you need to update the time yourself at runtime. If the device has an internet connection, it's quite easy to use an NTP server. An alternative for disconnected projects with access to a GPS receiver can be the high-precision time signal, sent by satellites. Go to the examples folder and run the following to update the time:
`
node set-date
Available Methods
===
update(line)
---
The update method is the most important function, it parses a NMEA sentence and forces the callbacks 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)
- satellites: Number of satellites being tracked
- hdop: Horizontal dilution of precision)
- geoidal: Height of geoid in meters (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
HDT - Heading
---
The parsed object will have the following attributes:
- type: "HDT"
- heading: Heading in degrees
- trueNorth: Indicates heading relative to True North
- valid: Indicates if the checksum is okay
GST - Position error statistics
---
The parsed object will have the following attributes:
- type: "GST"
- time: The time given as a JavaScript Date object
- rms: RMS value of the pseudorange residuals; includes carrier phase residuals during periods of RTK (float) and RTK (fixed)
- ellipseMajor: Error ellipse semi-major axis 1 sigma error, in meters
- ellipseMinor: Error ellipse semi-minor axis 1 sigma error, in meters
- ellipseOrientation: Error ellipse orientation, degrees from true north
- latitudeError: Latitude 1 sigma error, in meters
- longitudeError: Longitude 1 sigma error, in meters
- heightError: Height 1 sigma error, in meters
- valid: Indicates if the checksum is okay
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
- satsActive: Array of active satellites
- speed: Speed over ground in km/h
- track: Track in degrees
- satsVisible: 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.
Troubleshooting
===
If you don't get valid position information after turning on the receiver, chances are high you simply have to wait as it takes some time to first fix.
Functions
===
GPS.js comes with a few static functions, which helps 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.TotalDistance(points)
---
Calculates the length of a traveled route, given as an array of {lat: x, lon: y} point objects
GPS.Heading(latFrom, lonFrom, latTo, lonTo)
---
Calculates the angle from one coordinate to another. Heading is represented as windrose coordinates (N=0, E=90, S=189, W=270). The result can be used as the argument of angles compass() method:
`javascript`
const angles = require('angles');
console.log(angles.compass(GPS.Heading(50, 10, 51, 9))); // will return x ∈ { N, S, E, W, NE, ... }
Using GPS.js with the browser
===
The use cases should be rare to parse NMEA directly inside the browser, but it works too.
`html`
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
Dual licensed under the MIT or GPL Version 2 licenses.