Radar, Musk said, is problematic as a control mechanism for autopilot, because the signal doesn't readily distinguish between different types of objects. For instance, the dish-shaped bottom of a metal soda can reflects radio waves in a way that could make it appear to be a deadly obstacle. Yet those same waves will travel right through a solid oak tree, rendering it nearly invisible. To avoid constantly screeching to a halt in front of soda cans, Tesla's autopilot system did not treat radar data alone as sufficient to trigger emergency braking. Instead it relied on processing data from the car's video camera, which can readily identify many common obstacles based on their appearance.