The difference between 'local planner' and 'global planner' in obstacle avoidance

Hello, I’m trying to test ‘Obstacle Avoidance’ on my Pixhawk multi copter and rover. (final target is rover.)
Because this is my first time, I’m having trouble in selecting hardware.
I have just read about obstacle avoidance in drone code pixhawk user guide, and found that there is ‘local planner’ and ‘global planner’.
Seriously, I have no idea what is the difference between these two things.

Please tell me the difference, and if possible, just give me the recommendation some hardware like camera, and board. Thank you.