Photograph: Simon Hill Light Detection and Ranging (Lidar): This system, also used by self-driving cars, fires out rapid laser pulses to map the terrain in 3D. It enables mowers to cut grass under thick tree canopies or near tall buildings where GPS signals usually fail. AI Vision: Some mowers now employ cameras to recognize lawn areas, borders, and obstacles. Robot mowers with AI vision can potentially avoid stray footballs, cats, other critters, and maybe even pet mess. But they can also be too sensitive, stopping for fallen branches, leaves, or overhanging plants. Some of the top mowers, like the Mammotion I’m currently testing, employ a combination of the last three technologies to map and cut areas accurately, navigate reliably to and from the charging base, and avoid unexpected obstacles. None of them is foolproof. My top pick chewed up a deflated paddling pool, but if you set the sensitivity too high, they leave areas uncut. In addition to finding their way, many of the latest robot mowers are built to handle rough terrain. Not too …