At the moment, we don't have a way to track wrists or hands in general, only objects or images. Since a wrist cannot be scanned ahead of time, that only leaves image tracking.
The way to do this is to print an image that will placed on the user's wrist, similar to how it's done in this video. After that, in Unity you can simply align the augmentation to the image target.
How can I bind my 3d object to an object at runtime? I am using Unity currently.
Say, I am tracking my wrist. Now I want to render a watch on it. The Instant Tracking feature fixes the watch to a position relative to the ground. But I want to fix the watch to the hand.
How can I do it in both the following cases?
1. Assuming that I don't have the initial the position to bind the watch to
2. Assuming that I have the initial position to bind the watch to