新版Google地图如何使用iPhone的硬件来确定用户面向的方向？

The new Google Maps app allows you to select a destination, and then go into a mode where the map is constantly rotated in the direction you're facing, and it never asks you to calibrate the compass. If you spin in a circle, the map will spin with you, accurately rotating the map so that the direction you're facing always correlates with "up" on the map. As far as I know, this wasn't possible before. How do they do this? The new Google Maps app allows you to select a