There are two roles of boards:
- Position the camera in the level - moves the camera actor in UE’s world.
- Position tracked objects (those with a tracking-component) - many objects can be tracked at once.
You can change the size of markers (example in video)](https://youtu.be/Ys8br7AKW9g?t=2m55s).
But for the actual pattern on the marker, only ArUco is allowed, because the plugin finds all ArUco patterns from all boards in one pass, then passes them to each board for pose estimation.
Yes, once per camera - we need to find the focal length. Then the calibration result is saved to a file. If you know the camera’s focal length beforehand, you can write that file and skip calibration.
On Android the calibration may not even be necessary, because Android API gives the FOV angle (and the plugin uses it when no calibration was performed) - I don’t know how accurate that is however.
I use simple 2D UMG UI in the example project. A widget used to control the AR system is provided. The AR video stream is shown in the background and does not interfere with any UI.