Segway Navimow has two so-called "GPS" receivers. Actually, these days we use the term GNSS (Global Navigation Satellite System) instead of GPS because there are many satellite navigation systems circling the Earth. GPS refers to one specific constellation of satellites only, whereas GNSS refers to all of the systems. Navimow can detect and make use of all of these systems.

One receiver is in the mower itself (under the glowing ring) and the other is in the black box on a pole called EFLS (Exact Fusion Location System) aerial. Both receivers need to have a good view of the sky in order to detect enough satellites to determine the mowers location. It is especially important that the EFLS aerial has a good view of the sky, as the mower has other methods of determining where it is (VisionFence camera, for example). It is also important that the mower has a good view of the sky when it is docked in the Charging Station.

A radio signal from GNSS is relatively weak, and is attenuated (diminished) or blocked entirely by tall buildings, trees, water tanks and landforms such as hills.

Accordingly, it is important to carefully consider where you place the EFLS aerial and the Charging Station. Often, the EFLS aerial will be close to the Charging Station, elevated on a 1m pole. It is also possible to place it up to 10m away using the Segway Antenna Extension Cable, including up on a fence or on a roof using the Segway Antenna Extension kit. The general rule with radio signals is the higher the aerial (antenna) the better the signal/reception.

Here is an example of where not to install your Charging Station.

This location proved to provide only an intermittent GNSS signal to the mower when docked. Sometimes the mower would indicate a good signal via a green light ring on the top, and other times the ring would be yellow indicating a poor signal. When the installation was done the ring was green throughout, delivering a false sense of suitability for this location.

The ring colour would change as the constellation of satellites moved across the sky. The mower will not leave the Charging Station if the ring is coloured yellow.

Lets look at the Sky plot again, this time also considering the Top View:

And now, let's look at an example of the Navimow App's helpful Satellite Signal Analyser. This places Blue and Orange dots on the Top View. Blue dots represent satellites that both the mower and the EFLS are receiving signals from. The Orange dots represent satellites that only the EFLS is receiving signals from. In an ideal set-up the total number of dots will be high, and the number of Orange dots would be low. It is normal for the mower to "see" fewer satellites, especially if it is driving near a wall, under a tree, or some other obstruction to its view of the sky above.

It is not just the number of satellites in view, but also their elevation. Navimow wants to receive signals from a range of elevations to maximise the accuracy of its position.

Here's another example for the same Navimow set-up, captured at another time. Notice the change in the number of co-visible satellites, their distribution, and state:

Another important metric is how quickly Navimow is able to lock onto the signals being beamed down from the satellites. The faster the lock, the better. Here is an example showing a fast lock time.

And finally, let's apply all that we've discussed above to our original photo (the one showing where not to locate your Navimow Charging Station):

When you keep in mind that a concrete tank filled with water absorbs all GNSS signals, that trees attenuate the signal a bit, and wooden walls attenuate it somewhat, you can understand how in this location a Navimow docked in a Charging Station indicated by the yellow square has a very limited view of the satellites above. Yes, there will be times when there are sufficient satellites in view to provide a green ring, but also times when the ring will be yellow (meaning Navimow will stay home until the ring turns green).