Explanation of the mannequin IK bones?

Thing is, I’ve been able to do all of those things my way without the extra IK root bones which is why I’m confused why they exist.

I’d be interested in examples of why I need the IK Hand Root and IK Foot Root bones as opposed to having those just be children of Root itself. I’ve never seen IK Hand Root and IK Foot Root move away from Root.

Same with that Gun bone…

Here’s currently my setup just to clarify some more:



Root

    (Main Skeleton itself)
    Pelvis
        Spine 01
            etc...
        Left Leg
            etc...

    Left Hand IK Target
    Right Hand IK Target

    Left Foot IK Target
    Right Foot IK Target

    (Knee Pole Vector Targets, 2 Bone IK has the option of specifying these)
    Left Knee IK Target
    Right Knee IK Target

    (Elbow Pole Vector Targets)
    Left Elbow IK Target
    Right Elbow IK Target


This is the setup used in Unreal 4 Mannequin that I’m trying to understand



Root

    (Main Skeleton itself)
    Pelvis
        Spine 01
            etc...
        Left Leg
            etc...

    Hand IK Root (Not sure what this extra hand IK root is for)
        Gun (Located at the right hand)
            Left Hand IK Target
                Right Hand IK Target

    Foot IK Root (Not sure what this extra foot IK root is for)
        Left Foot IK Target
        Right Foot IK Target


    (Also in UT4 I saw there were a few extras, not sure if these are even used, maybe for legacy UT3 anims because this is how it was in UDK)
    Hand IK Root Alt
        Left Hand IK Target
        Right Hand IK Target

    Foot IK Root Alt
        Left Foot IK Target
        Right Foot IK Target


With my setup, I plan on having either the left hand or the right hand reach out to interact with arbitrary objects in the world. I currently have it working beautifully for holding different sized guns by making the left hand move to the correct spot on the gun with IK. I had to modify existing Skeletal controls a bit which I can describe how if anyone’s interested but it works in the end.

Also in Maya my control rig is set up so I control knee and elbow directions using pole vector targets. And I can constrain the bones in the skeleton to those controls as well so what I do in Maya matches exactly in game.