1 FOOT ARCH and KNEE JOINT
 

Another thing that is captured in MOCAP data is the SPRING that happens in the ARCH of the FOOT from the WEIGHT of the BODY compressing downward. MOCAP captures very accurately and catches all those little intricacies. And when this MOCAP data is translated onto an IK Rig those fractional movements are not taken into account.

Most IK rigs lock the foot in place with one joint and don’t take into account this SPRINGY action of the ARCH. And that will result in floaty looking feet, because the MO CAP data is SPRINGY and the IK Rig is RIGID.  And then there is a conflict with the axis lining up and that is why on some moves feet can look ok but on others where arch compresses it does not line up.

When running and doing quick movements the arch compresses more than when walking or tip toeing. So this height is not fixed and moves upward and downwards.

So this is even more evidence on why it is best to KEY out the Footsteps to look SOLID and then retarget the Mocap data onto Solid footwork. By rempapping on KEYS it eliminates all these fractional variables and makes the mocap data look SOLID.

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  PLUS The Ankle JOINT also can move slightly to the LEFT and RIGHT and Most IK rigs only lock the foot in one AXIS.
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  And there are different FOOT ARCHES and depending on the ANATOMY of the PERSON that will also cause conflict in lining up the IK Rig. Notice how the ankle height changes depending on foot type. Also a more arched ankle will be more flexible then one that is flat footed. If you capture a flat footed actor and put it on a high angle rig -there will be mis alignment issues.
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  In a living human even a few fractions off on your foot alignment that will cause pain. And that is why they make insoles to compensate for alignment issues. So those little fractions do make a big difference - even with mocap data in the virtual world.
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Also moving up the hierarchy. The KNEE JOINT moves slightly left to right and even slightly forward. Minor fractions but still caught by mo cap. Also most IK rigs lock the knee joint into one position. The knee does move slightly left and right. So its really a 2 pivot system.

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This is all really noticeable on a ballet dancer. Because they have extreme control of the arch of their feet.

   
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