Questions on frameplacement

[xiaosuyang]

Hello.
I found that both functions updateFramePlacement() and framesForwardKinematics() are used to calculate the placement of each frame. So what's the differences between them.

Besides,the model.frame[frame_id].placement return the placement with respect to parent joint, how to get the placement wrt the Base_link or world_frame?

Finally，for a legged robot, what's the position of the "world_frame“, is it a inertial frame whose origin coincide with base_frame(torso) or just a fixed point on the ground?

[stephane-caron]

I found that both functions updateFramePlacement() and framesForwardKinematics() are used to calculate the placement of each frame. So what's the differences between them.

From the documentation of updateFramePlacement and framesForwardKinematics:

• For the former: "One of the algorithms forwardKinematics should have been called first" (framesForwardKinematics is one of these algorithms). As a consequence there is no configuration vector q in the parameters, but there is a frame_id as it will only update the placement of one specific frame.
• For the latter: "First calls the forwardKinematics on the model, then computes the placement of each frame."

Therefore, we don't need to call updateFramePlacement if we call framesForwardKinematics, as it will update all frame placements (same effect as calling updateFramePlacement on every frame_id, although it will of course be done all at once and more efficiently).

This is only for your first question. Try opening a separate discussion for each question so that we can organize the conversation better.