I am using ARCore to track an image. Based on the following reference, the FOCUSMODE of the camera should be set to FIXED for better AR tracking performance.
Since for each frame we can get camera intrinsic parameter of focal length, why we need to use a fixed focus?
With Fixed Camera Focus ARCore can better calculate a parallax (no near or distant real-world objects must be out of focus), so your Camera Tracking will be reliable and accurate. At Tracking Stage, your gadget should be able to clearly distinguish all textures of surrounding objects and feature points – to build correct 3D scene.
Also, Scene Understanding stage requires fixed focus as well (to correctly detect planes, catch lighting intensity and direction, etc). That's what you expect from ARCore, don't you?
Fixed Focus also guarantees that your "in-focus" rendered 3D model will be placed in scene beside the real-world objects that are "in-focus" too. However, if we're using Depth API we can defocus real-world and virtual objects.
P.S.
In the future ARCore engineers may change the aforementioned behaviour of camera focus.
