问题 After some testings by printing faceAnchor.transform.columns.3 , digging in SO: ARFaceAnchor have negative Z position? and Apple's documentation: ARFaceAnchor, I realized that the z axis is actually flipped and it is not the right-handed coordinate system as in the documentation. The ARFaceAnchor claims the coordinate: the positive x direction points to the viewer’s right (that is, the face’s own left), the positive y direction points up (relative to the face itself, not to the world), and