Daniel sees a video of a Waymo robotaxi driving through San Francisco with nobody in the front seat.

He assumes it must be following GPS.

It is doing something far more interesting.

The car is constantly answering four questions: Where am I? What is around me? What might happen next? What should I do? It answers all four simultaneously, in real time, without a human involved.

Before Waymo operates in a new area it builds extremely detailed maps -- lane markings, curbs, crosswalks, signs and signals. While driving, the car matches what its sensors are seeing against those maps to locate itself precisely. GPS helps, but the car is also recognizing the world around it.

Three kinds of sensors feed the system. Cameras give it visual detail -- traffic lights, signs, lane markings, pedestrians and cyclists. Radar measures d ...