gps

Overview

The gps node reads position data from any NMEA-compatible GPS/GNSS receiver via a serial connection. It parses standard NMEA sentences (GGA, RMC, GSA, GSV) to provide latitude, longitude, altitude, speed, course, satellite count, fix quality, and dilution of precision. Works with any generic GPS module that outputs NMEA data over UART.

Properties

Output

{
  "latitude": 51.5074,
  "longitude": -0.1278,
  "altitude": 11.2,
  "speed": 0.52,
  "course": 215.3,
  "satellites": 9,
  "fix": "3D",
  "hdop": 1.2,
  "timestamp": 1640000000000
}

Wiring (UART)

  GPS Module         Raspberry Pi
  ----------         ------------
  VCC  ──────────── 3.3V (Pin 1)
  GND  ──────────── GND  (Pin 6)
  TX   ──────────── RXD  (Pin 10 / GPIO 15)
  RX   ──────────── TXD  (Pin 8  / GPIO 14)

  Note: TX on GPS connects to RX on Pi
        (and vice versa - crossed)

Example: Geofence Alert System

Monitor GPS position and trigger alerts when a device enters or leaves a defined geofence area.

// Function node: Geofence check
var lat = msg.latitude;
var lon = msg.longitude;

// Define geofence center and radius (meters)
var fenceLat = 51.5074;
var fenceLon = -0.1278;
var fenceRadius = 500; // meters

// Haversine distance calculation
var R = 6371000; // Earth radius in meters
var dLat = (lat - fenceLat) * Math.PI / 180;
var dLon = (lon - fenceLon) * Math.PI / 180;
var a = Math.sin(dLat/2) * Math.sin(dLat/2) +
        Math.cos(fenceLat * Math.PI / 180) *
        Math.cos(lat * Math.PI / 180) *
        Math.sin(dLon/2) * Math.sin(dLon/2);
var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a));
var distance = R * c;

var inside = distance <= fenceRadius;
var prevInside = flow.get('insideFence');

msg.payload = {
    latitude: lat,
    longitude: lon,
    distance: distance.toFixed(1),
    insideFence: inside,
    event: (inside !== prevInside) ?
        (inside ? "entered" : "exited") : "none"
};

flow.set('insideFence', inside);
return msg;

Example: Vehicle Trip Logger

Log GPS data points during a vehicle trip including distance traveled and average speed.

// Function node: Trip data logger
var lat = msg.latitude;
var lon = msg.longitude;
var speed = msg.speed; // km/h
var trip = flow.get('trip') || {
    start: null, distance: 0, maxSpeed: 0,
    points: 0, lastLat: null, lastLon: null
};

if (!trip.start) {
    trip.start = msg.timestamp;
}

// Calculate distance from last point
if (trip.lastLat !== null) {
    var R = 6371000;
    var dLat = (lat - trip.lastLat) * Math.PI / 180;
    var dLon = (lon - trip.lastLon) * Math.PI / 180;
    var a = Math.sin(dLat/2) * Math.sin(dLat/2) +
            Math.cos(trip.lastLat * Math.PI/180) *
            Math.cos(lat * Math.PI/180) *
            Math.sin(dLon/2) * Math.sin(dLon/2);
    var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a));
    trip.distance += R * c;
}

trip.lastLat = lat;
trip.lastLon = lon;
trip.points++;
if (speed > trip.maxSpeed) trip.maxSpeed = speed;

flow.set('trip', trip);

var elapsed = (msg.timestamp - trip.start) / 1000;

msg.payload = {
    position: { lat: lat, lon: lon },
    speed: speed,
    distance_km: (trip.distance / 1000).toFixed(2),
    elapsed_min: (elapsed / 60).toFixed(1),
    maxSpeed: trip.maxSpeed.toFixed(1),
    satellites: msg.satellites,
    fix: msg.fix
};

return msg;

Common Use Cases