What does the Fixed Frame mean in rviz?

edit

Thank you so much.

Does the Grid always be the world coordinate? If I set /odom as the fixed frame. Rviz will draw obstacle at potions (10, 5) in the Grid?

I think the heading in your assumption should be pi/2.

Yeah, fixed that, sorry. Need coffee.

And yes, if you set the fixed frame to /odom, the obstacle will be drawn at (10, 5).

@tom, I didn;t really follow your explanation, what does heading = pi/2 mean ( is the robot facing left by 90 degree compared to lidar) ?

also could you elaborate how the (10,0) and (10,5) works out ? can't seem to visualize that based on the explanation.

What happens If I keep my fixed_frame as /map instead of /odom and /base_link frame?

Then you will see everything displayed in the map frame. In my drawing, just imagine another coordinate frame like the odom frame, but not with the same origin/position.

All the fixed frame does is define where the origin is when rviz displays things.

I'll just write what I understood from this, let me know if I'm wrong. So the map frame is linked to the environment and the odom frame is linked to the starting point of the robot on the map.