HALIUM
Halium is an open-source project which bridges the gap between Android hardware abstraction layers (HAL) and Ubuntu Touch. It leverages libhybris, which allows the system to use Android hardware drivers, making it possible to use hardware like camera's and sensors. libhybris in effect translates Android-specific drivers to non-Android Linux kernels.
The way to port.
Almost all modern Ubuntu Touch ports run on top of Halium. This makes it
possible to use hardware that normally wouldn't work, such as on-device
camera's or biometric authentication.
A common base.
While every device is different, Halium offers a common base that makes
porting Ubuntu Touch a tad easier. You only care about the specific
hardware that you're working on.
Detailed docs.
Halium offers detailed documentation on how to start porting to your device, making it easier to get your foot in the door.