Yes, an RTK mower needs a clear line of sight to the sky for satellite signals, and ideally between the mower and the base station if you use a local base station. RTK (Real Time Kinematic) positioning works by comparing signals from the same satellites at two receivers, the mower and a fixed base station. If trees, buildings, or other obstacles block the view, the mower can lose accuracy or even stop navigating correctly. The answer is not absolute, however. Some RTK systems can compensate for brief obstructions, but a permanently obstructed sky or base station link will degrade performance.
Understanding RTK and Line of Sight
RTK mowers use two GPS receivers: one on the mower and one at a fixed base station. The base station sends correction data to the mower via radio or cellular link. Both receivers need to see the same satellites to calculate a precise position. If the mower loses sight of the sky, it cannot track satellites. If the mower loses sight of the base station, it cannot receive corrections.
For the satellite link, the mower needs a clear view of the sky above about 15 degrees elevation. The base station also needs a similar clear view. For the radio link between mower and base station, line of sight means direct visibility without obstacles. This is especially important for UHF radio links, which cannot penetrate buildings or dense foliage.
How Satellite Communication Works
GPS satellites orbit high above the earth. A receiver must have a direct line of sight to at least four satellites to calculate a 3D position. RTK requires even more precision, typically four or more satellites with a strong signal. Obstructions like trees, houses, or hills block these signals. Even a partial blockage can reduce the number of visible satellites and cause accuracy to drop.
Modern RTK receivers can use multiple GNSS constellations (GPS, GLONASS, Galileo, BeiDou) to increase satellite availability. This helps when part of the sky is blocked, but it does not eliminate the need for a clear view. The mower will still need to see enough satellites from any constellation.
Common Obstacles That Block Signals
The most common obstacles are tall trees, buildings, and steep terrain. Trees with dense foliage can block or weaken satellite signals. Buildings can create a complete shadow. Even a single large tree can cause the mower to lose its position near the trunk.
Obstacles between the mower and the base station are equally problematic. If the base station is placed behind a house or in a low spot, the radio link may fail. The mower may then drift or stop moving until it regains the link.
The Role of the Base Station
The base station is the fixed reference point. It must have a clear sky view to collect satellite data. It also needs a clear line of sight to the mower for the correction link. The distance between base station and mower can be up to several kilometers with a good radio link, but obstacles shorten that range.
Some RTK systems use a network of base stations (like a cellular RTK service) instead of a local base station. In that case, the mower still needs a clear sky view, but the base station link is handled by the network and does not require direct line of sight. However, cellular coverage must be reliable.
What Happens When Line of Sight Is Lost
If the mower loses satellite signals, its position accuracy degrades from centimeter level to meters or worse. The mower may stop, turn around, or drive erratically. If the base station link is lost, the mower may revert to standard GPS, which is not accurate enough for lawn mowing patterns.
During brief dropouts (under a few seconds), the mower’s internal sensors can sometimes keep it on track. But prolonged loss of line of sight will cause the mower to fail its mapping or navigation. This is why manufacturers recommend a clear yard for RTK mowers.
How to Improve Line of Sight
You can improve line of sight by placing the base station in the highest, most open part of your property. Mount it on a pole or rooftop to clear obstacles. Trim overhanging branches if possible. For the mower, consider clearing large bushes or trees near the mowing area, but that may not be practical.
If you have a very obstructed yard, a cellular RTK service (which uses a network of base stations) may be a better option. Alternatively, you can use a robot mower that does not rely solely on RTK, some combine RTK with other sensors like vision or lidar. But those are topics for other articles.
How to Fix / What to Do
- Place the base station high and unobstructed, ideally on a roof or pole.
- Trim trees or branches that block the mower’s sky view.
- Check the radio link between base station and mower, if it fails, move the base station closer or higher.
- Consider using a cellular RTK service if your yard has many obstacles.
- Test the mower in different areas of the yard to identify dead zones.
If you want a deeper understanding of RTK precision and what affects it, read our article on how accurate RTK robot mowers are. It explains the factors that influence accuracy, including line of sight.
Frequently Asked Questions
Can an RTK mower work without any line of sight?
No. An RTK mower needs at least a clear view of the sky to track satellites. Without any line of sight, it cannot calculate its position. However, brief dropouts of a few seconds may be tolerable if the mower has inertial sensors to keep it on track.
Do trees completely block RTK signals?
Dense tree foliage can weaken or block satellite signals, especially in heavy rain or when leaves are wet. Sparse trees may still allow signals through, but accuracy will suffer. For reliable operation, the mower should have a clear view of the sky above the tree line.
How far can the base station be from the mower?
With a clear line of sight, a UHF radio link can reach several kilometers. With obstacles, the range may drop to a few hundred meters. Cellular RTK services eliminate the distance limit, but require a cellular data connection.
Does rain or snow affect RTK line of sight?
Heavy rain or snow can attenuate satellite signals, but the effect is usually minor. The bigger issue is that wet foliage blocks more signal than dry foliage. Snow on the ground does not affect the mower’s sky view, but deep snow can cover the base station antenna.
Related Guides
Closing
In short, an RTK mower does need line of sight to the sky and to the base station for optimal performance. You can improve the situation by placing the base station high and clearing obstacles. For a deeper look at how RTK works and how to get the most out of it, see our guide on what RTK is on a robot lawn mower.
