What it is
GPS is the satellite navigation system operated by the United States. A receiver listens to timing signals from several satellites at once and works out its own latitude, longitude and altitude from how long each signal took to arrive. It needs at least four satellites for a full 3D fix, and works best with a clear view of the sky.
Modern receivers usually use more than one constellation, GPS alongside Galileo, GLONASS and BeiDou, which together are called GNSS. A receiver reports its position, speed, heading and the quality of the fix, commonly as NMEA sentences over a serial line, which a small computer such as a Raspberry Pi reads and turns into messages.
How I use it
- I build trackers on a Raspberry Pi with a cellular shield and a GPS receiver, so a machine reports its position from a yard, a job site or the road.
- Every message carries latitude, longitude, speed and the quality of the fix alongside power-on and run hours.
- The pattern I build with keeps the latest position of each machine in DynamoDB and every fix in S3, so trails can be replayed.
- Geofences around each job site raise an alert when a machine leaves, and movement with the key off is treated as possible theft.
- The tracker reports often while moving and rarely while parked, which keeps the data plan small without losing the trail.
Location is the reading that matters most when the thing you own is out in the world. A GPS fix in every message says where a machine is now, and keeping every fix says where it has been: when it left the yard, how long it sat on a site, and whether it moved when it should not have. Paired with a cellular shield, it works anywhere there is signal, with no Wi-Fi.
Questions
How accurate is GPS on a tracker?
Outdoors with a clear sky, a few metres is typical for a consumer receiver. Accuracy drops near tall buildings, under heavy cover and indoors, which is why each message also carries the quality of the fix.
Does GPS tracking need Wi-Fi?
No. The receiver only listens to satellites. Getting the position back to you takes a network, and a cellular shield on the tracker sends it from anywhere with signal.
Can a GPS tracker spot theft?
It can spot the pattern: a machine moving with the key off, after hours, or outside its job site. Those rules raise an alert with a live map link while it is still moving.