How do self driving cars know where they are?

While the LiDAR, radar, and cameras on a self driving vehicle are able to inform the car about its surroundings, without GPS, how would the car know which road it is on or how to get to its destination without a human controlling it?

To do so, a Global Positioning System uses satellites to triangulate the geographical position of its reciever. This allows any device with a GPS receiver to know within a roughly two meter accuracy where it is and does so without any cellular or wifi connection and is independent of any weather conditions or the location of the receiver on or near the planet. All that is required for these devices to function is a connection to four or more satellites.

When it comes to autonomous vehicles, GPS is not quite accurate enough to tell a car where it is in a lane or in respect to other vehicles with GPS, but it still can be very useful for navigation and applications of LiDAR. For example, as we learned in class this week, some car companies think that it is more economically feasible to pre-scan roads with LiDAR just once and then use a GPS tag on those LiDAR scans to help the car know which lane it is in and such. Because cars like these Cadillacs have no aboard LiDAR, they rely on their GPS to utilize their LiDAR and cameras and radar to sense other vehicles.

The leader in the GPS receiver production field is currently NovAtel who claims they have GPS with 1.5 meter accuracy and is used by many self driving car companies.