Questions on the inverse kinematics parameters

[mfouadthabet]

I cannot figure out what are exactly L1, L12,L2 , L3 which are used in the solve_ik function.

My best guess is that L1 , L2 are distance between waist pitch and knee , knee to ankle pitch respectively. Where L12 is distance between waist roll and waist pitch and finally L3 is distance between ankle role and ground. Also it is assumed that ankle pitch and ankle role z distance is 0 , also waist pitch and waist roll z distance is 0.

Still the calculations in IK does not add up correctly.
What is Knee_displ , knee displacement ?
Can you provide any details on the IK calculations and specially the derivation of the knee_pitch from knee_disp

Thanks in advance.