I decided to use the 2 contacts sensor as "rotary encoder" to decode the garage door position. Basically, it uses 2 contact sensors and a magnet. The 2 contact sensor is placed in parallels about 2 inch a part. The magnet is installed on the pully of the garage door. The magnet will approach the 2 contact sensors. We can tell whether the garage door is opening or closing by looking which contact close first. It is important for the event from the contacts come at the right order. We then can count the position of the garage door.
The 2.29 update help to make this much more reliable. Thanks to @gopher.ny and Hubitat team for the single thread option.
Here is a short 32 seconds demo to test the concept. I am happy with the result. This will open a path for me to partially open the door in the future.
