Before getting Nofence
Understanding GPS accuracy and drifting
Understanding GPS accuracy and drifting
Understanding GPS accuracy and drifting
Understanding GPS accuracy and drifting
The Nofence collar uses GPS satellite signals to determine its location and decide when to emit an audio warning or electric pulse. Because it is GPS (not the mobile network) that keeps the virtual fence active, your livestock will remain contained even in areas with no mobile coverage.
How GPS accuracy changes near the boundary
To balance battery life and precision, the collar uses more power the closer it is to the boundary to ensure maximal accuracy of the warning sound. Further away, position logging is reduced to save power. As the animal approaches the boundary, the collar increases its accuracy and update rate to ensure warnings and pulses are delivered at the right time.
Distance from the Nofence boundary | GPS accuracy |
More than 12 metres | Zone with increased power saving |
12–6 metres | The GPS receiver prepares. It prioritises performance over power saving, but updates no more than once per second |
6–0 m metres | Maximum performance with four position updates per second. The collar is preparing to play the audio warning |
Outside the Nofence boundary | The collar alerts the animal that it is outside the pasture by emitting the audio warning. The collar continues to report the animal’s position even when outside the boundary. |
What affects GPS accuracy
Satellite coverage is generally good, especially in open landscapes. However, several factors can reduce precision:
Distance from the boundary. The accuracy of the animal’s location is intentionally reduced as the animal goes further from the boundary. When the animal is further from the boundary, the collar goes into a GPS power saving mode, meaning that it sees fewer satellites. This is to conserve battery. As the animal approaches the boundary, more satellites are seen, and accuracy is increased. This feature only affects the accuracy of the location as it is shown in the app; it does not affect the maintaining of the virtual boundary.
Number of satellites. Nofence continually scans multiple satellite networks. The number of satellites visible at any location varies throughout the day.
Topography. Steep mountains, narrow valleys, and natural corridors can reduce signal quality. Nofence can still be used in these areas, but a slightly larger tolerance for variation may be needed.
Buildings, structures, and tree coverage. Roofs, walls, and trees can all block or reflect GPS signals, which can cause inaccurate positioning. Forest grazing can therefore be less accurate than open pastures, but we have many good user stories where it works perfectly fine.
Note: When animals are not moving (especially while sleeping), the GPS is turned off. In this case, the collar will report the last known position, and comes back on as soon as it detects movement.
What is drifting?
Drifting is what happens when a GPS receiver logs an incorrect position. It is a well-known limitation of GPS technology, and can affect any GPS device. With Nofence collars, drifting is most likely to occur in two situations:
Near buildings. Roofs and walls can interfere with the GPS signal, causing the collar to think it is in a different location than it actually is.
When an animal is resting near the boundary. Positions sometimes might be less accurate immediately after turning GPS on, which happens if the animal wakes up after resting. If the collar drifts into an incorrect position outside the boundary, the collar may emit an audio warning. The animal would then need to move further into the pasture to stop the warning.
If the system cannot detect that a position is false, it will act on that position. This means an animal could receive an audio warning or pulse while it is still safely inside the pasture.
The risk of this happening is low, but it can occur if the collar enters sleep mode when it is close to the boundary. We recommend leaving a safe margin between resting areas and the virtual boundary where possible.
Reducing drifting by using shelter beacons
If your livestock have access to a barn, shed, or any sheltered structure, we strongly recommend installing shelter beacons. A shelter beacon disables the GPS receiver when a collar is within range, preventing the collar from logging false positions caused by signal interference. This eliminates unwanted warnings while animals are inside.