What is it? ex)getPlayer()->yaw; getPlayer()->getYaw(); and Additionally, Is Yaw's Base point left(0degree) so when it changing to +direction , it moves to right?
It should return the same values. I'm not sure about the second question, but I think it's like rotation to left -> +yaw. However all these things you can test by debugging.
getYaw is just a method that returns the yaw property: https://github.com/pmmp/PocketMine-...be5/src/pocketmine/level/Location.php#L63-L68