PDA

View Full Version : why empty groups?


brueghel
01-13-2010, 02:52 PM
Hello,

Im learning character rigging after a tutorial and I wonder why all the contollers of a rig are put in empty groups. It would help a lot if somebody could explain that.

Darksuit
01-13-2010, 03:45 PM
A null group or an empty group is a really useful thing. It doesn't render, or doesn't have a physical renderable mass. Therefore it only exists as a pivot location. This is a great thing. Basically you can group everything under the object and move evething as a whole or just by using the "insert" key you can move the pivot location where ever you need to.

In some cases an empty group is a stand-in for an any object. Since any object can have items grouped under it and can be moved, etc... a group does a good representation of an any object so that you don't get stuck on it has to be such and such.

Matt Leishman
01-13-2010, 04:11 PM
Many times in rigs you'll find that animation controls, those creatively shaped nurbs curves all over the rig, are in many different locations in 3d space around the character (depending on which limb or part of the body they are associated with). For efficient and clean animation of these controls they need to NOT have numbers populating their tran/rot/scale attributes when the rig is in its initial rest state. If you created an animation control for the hand ik out of a nurbs curve, then you'd have to position and orient it appropriately with the wrist of the character ... if you did this without a null node above it in the hierarchy then your wrist ik animation control would have populated tran and rot channels. This is bad. BUT, if you create the control curve, THEN parent it to a null group node and THEN move and orient that parent null node to the wrist of the character, the control curve itself retains its clean tran and rot channels with a value of zero.
This is part of the reason you will see many null group nodes all over a rig hierarchy ... for me its one of the most important reasons.

Remi
01-13-2010, 04:12 PM
Also keeps the outliner clean and organized. There's a lot of reasons for using them, and you can make up your own reasons if you want.

brueghel
01-13-2010, 04:41 PM
Ah Thanks,

if I move the null node I have the values of the position in world space, but the controllers itself is clean, or is it more useful to have both values clean (null node & controller)?

Matt Leishman
01-13-2010, 05:41 PM
the animator will not be accessing the null group nodes at all (they should not even be given access to them if it can be helped), they'll be accessing and using (setting keyframes on) the control objects. so it doesn't matter that the null group nodes have values in them. that's the point really ... they have the tran/rot/scale values so that their child (the control object) doesn't have them. animators like to be able to take any and every control object and zero them out and have that control go back to its initial rest position. this whole technique allows that to happen.

NolanSW
01-14-2010, 05:38 AM
Just to add, to be even more clean and keep those pesky animators from touching nodes that they shouldn't, lock and hide all the null groups channels. That way in the off chance they pickwalk up from a control to a null group they don't either key this group (which could break the control) or transform it which will break the setup.

Matt Leishman
01-14-2010, 04:14 PM
Pesky indeed ;)

Remi
01-14-2010, 04:31 PM
"Riggers" don't know what they're talking about:D

NolanSW
01-14-2010, 06:37 PM
"Riggers" don't know what they're talking about:D

You shut your pie hole ;).
You animators would be animating boxes and squash and stretch balls without us "Riggers".
Just some friendly ribbing.

CGTalk Moderation
01-14-2010, 06:37 PM
This thread has been automatically closed as it remained inactive for 12 months. If you wish to continue the discussion, please create a new thread in the appropriate forum.