Setup Degrees of Freedom before you apply Human IK onto your rig!
HumanIK system is come from Montion Builder. It usually use in motion capture. Today, I want to talk about Degrees of Freedom. As an animator, if you had a chance to use HIK, and also pay attention to the rotation of elbow, knee, ect... It is obviously to found out the elbow control has three rotation value which annoyed animators a lot.
To avoid this problem. In Maya, select the elbow/knee joints, then start check out the option on Attribute/ Limit Information/ Rotate.
In moition builder, go to properties panel. switch the filter to All(type). the Degrees of Freedom should be listed on the panel.
Notice! This setting could only apply on skeleton not HIK.
Let's take a look curves on this picture
Right side with yellow circle shows the result with DOF.
The biggest different is Forearm FK controller.
I will discuss T-Pose next time.
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在套用Human IK到骨骼之前， 先設定Degrees of Freedom!
HumanIK是來自Montion Builder的控制器系統，最常被運用的地方應該就是motion capture。今天為什麼我講講Degrees of Freedom，身為一個動畫師，如果你有用過HumanIK，是有過什麼手肘、膝蓋等關節處，旋轉值不會只有一個，而是x、y、z都有。正常用IK Solver不會有這種問題，設定FK時也會限制旋轉軸向，而這些動作也是可以在HumanIK上設定的，但卻一直沒人去重視這個部分，實在很讓人頭痛。
避免這個問題，一開始在設定骨骼時，在maya裡只要針對手肘、跟膝蓋去勾選Attribute/ Limit Information/ Rotate下的最小跟最大值，就可以減少動畫師在調整手肘跟膝蓋時的麻煩。
而在motion builder 裡則是稱作Degrees of Freedom(DOF)，在Properties裡先將顯示改成All(Type)就可以看到Degrees of Freedom的項目
只要在骨骼上設定好，HIK基本上就會依照骨骼的限制產生對的值，也就只會有一個旋軸的值。如果不做這個設定，當mocap的動作一套用上去，那HIK就會很"自由"的調動3個旋轉軸向。
看一下這張範列圖的曲線
右邊有紅圈的沒設置DOF
左邊有黃圈的是有設置DOF
最大的差別在前手臂的FK曲線
下次再談談T-Pose
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