Since this is an area of some confusion for animators learning to to use Maya, here's a brief outline of what the rules of World Control Etiquette really are.
So, what is the world control anyway?
The World control is the control on a character or creature rig which allows it to be moved into position. It is also sometimes called the World Mover, the Global Control, or the God Control. It is at the very top of the animation hierarchy, and supersedes all the other controls, hence its name.
What is it used for?
The World Control is used to place your character in your 3D set. That is generally the first and last time that you will use it.
Why should you not use it for animation?
Because it creates confusion. If you set keyframes on your world control to move your character, you will have to counter-animate other controls such as the body and the feet. This will create two sets of curves which counteract one another, and make it very hard to edit your curves.
So why in the Animation Apprentice tutorials do you sometimes animate on the World control?
Good question. The reason is that sometimes you have no choice. For example, if you are animating a walk cycle "on the spot", you may need to set a keyframe on the World Mover in order to create a sense of forward movement. This is because training rigs are generally highly simplified to make learning Maya easier. On production rigs, which tend to be very complex, there would likely be a series of controls below the World Control in the hierarchy which perform the same function as the World Control, but are called something different, such as the "Direction Control". So, on a production rig, you would use one of these other controls to create the same function, while leaving the World Control untouched.
So it is bad to animate on the World Control?
Generally, yes. But when you are animating motion cycles with simple rigs, then you may have no choice.
I learned the hard way not to use the world control when I was animating on "Robots", my first cg feature film. I was both an experienced animator but also a rookie when it came to cg, and I made the basic error of key framing the world control when I blocked out my first shot. When my animation lead found out what I had done he said "you'll have to start over". "really?" I asked, surely it can just be tweaked?". "No", came the answer, "you'll have to do it again".
It was a lesson I didn't have to learn twice.
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