Revision history [back]

You can think of base_footprint as ; projection of odom frame onto the ground plane, which is mostly used for object collision detection/avoidance algorithms. odom's roll and pitch angles can be changed during the movements of robot, however in base_footprint

With respect to the odom frame, the roll and pitch angles should be zero and the yaw angle should correspond to the base_link yaw angle.

Rationale: base_footprint provides a fairly stable 2D planar representation of the humanoid even while walking and swaying with the base_link.

you can also refer to here for some more details.

also have look at the similar discussion in this topic; here