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View Full Version : Local Rotation Axis - Is there a right and wrong?


Leffler
11-19-2008, 05:10 PM
Hello!

Iīm a bit confused about what Local Rotation Axis to have on my joints.

Right now I rig my characters so that all joints have x running along the chain pointing to the next joint and then Z is pointing forward(the direction the character is looking). Y pointd out to the side.

But then I looked at this page (http://student.vfs.com/%7Em07goosh/rigging101/free/ikleg/index.htm) and he says the orientation should be Y pointing down the chain

Is there a right and a wrong orientation? What do you guys use?

// Otto

edwardG
11-19-2008, 07:11 PM
At my last job I had to use z-down the bone because that's how the game engine read the rotation order.

I will otherwise point X down the bone usually.

It really doesn't matter too much in the end; they are all values and they all can be read by the machine, you just have to specify the relationship.

PEN
11-20-2008, 12:52 AM
The orientation of the axis isn't what you need to concern your self with it is the axis order. That being said the oriention of the axis will will cause or correct gimble problems. Really it is the axis order that you need to concern your self with. In any given axis order it is the middle axis that will cause the gimbling effect in an euler rotation. What you need to do is try and make sure that the joint you are working on frozen or reset in the default position so that it is as far from gimble as it can be and that in the extream orientations that it aviods gimble lock as much as possible. In a typical human rig this is just about always possible except in the most extreme orientations. To see gimble happen change to gimble more in what ever software you are in and then rotate the middle axis of the object 90° change the axis order and do it again and you can see that it will not happen. Now select the axis that is the middle of that axis order and rotate 90° and you will see it will happen again. It is less of a concern for your bones then it is your control objects as that it what is getting the input from the end user.

Tollman
11-20-2008, 11:44 AM
I agree with PEN in some aspects, that rotation order is important on the controls, but also on the joints, course if you are to connect attributes from your control to the joint and not use a orient constraint, witch is a tad heavier to calculate, you are going to have problems with the joint not acting as it should since the joint won't rotate as the controls does.
But the question was about local rotation, and there is no right or wrong, nor no wrong way to use them, it will just be a heck lot easier if you are consistent with them.
in most of the cases, you want one axis down the child, (exceptions are the wrist joint, where you want the rotation axis to be straight out form the arm, and not aligned to a joint in the hand. it often works if you point it down the middle finger joint.)
I for one use always X down the child, then also i orient the the way that when you rotate all joints in the rig to positive Y, the rig goes into foetal position and folds inwards. this way you always know what happens in the graph editor when you add to the y value.

X down the hierarchy is the common way.

Y is often forwards, but that bends the knee and the elbow in different directions and will just get messy.

Z is driven by the other two.

this is my way, hope it helps.

//Jonas

Leffler
11-20-2008, 01:24 PM
(exceptions are the wrist joint, where you want the rotation axis to be straight out form the arm, and not aligned to a joint in the hand. it often works if you point it down the middle finger joint.)


Hej Jonas,

So if i understand correct, you have X pointing in the direction of the characters nose in wrist?
Why? I donīt understand the reason for that

Donīt understand what you mean with "it often works if you point it down the middle finger joint" either ...

// Otto

Tollman
11-20-2008, 01:45 PM
:hmm: hmm, how will i explain this??

rather than having the x axis on the wrist joint go out to the pinky or thumb, you would have it point straight out, kind of following the line of the middle finger, since it is the center finger of the hand.
course if you have the x axis straight out, you can align the Y axis so that when you rotate just the Y, you get the hand to bend downwards, and not in some strange direction.
http://www.jonasborgman.com/hand.jpg
the image shows a hand, whatever you may say.

//Jonas

MolemanSD7
11-20-2008, 02:07 PM
I concur with what was said above. The only other thing to remember is to be consistent. Make sure all the joints are setup similarly. Its an obvious point, but if its overlooked, it can cause a real headache if you get too far along.

c000be
11-20-2008, 07:14 PM
i usually follow x axis down, but what i really want to know is about that last joint in the chain, the one that never lines up the way the others do, because the x doesn't have a 'child' to follow.
should the axis to that be rotated [never via gimbal, from what i've heard], especially if you're going to be parenting other chains to it?

and why can't i get the iKhandle to work. i drew a chain, did the iK handle in the right order, i know the iK handle doesn't show, so i'm supposed to work the nurb's/cv/s in component mode to move the chain, and ...noth-ing..nadda. what is going on? maya 2008.

stewartjones
11-20-2008, 11:04 PM
To orient your end joint correctly. Use the Orient Joint Tool in Maya. Open the options and set the Orientation to 'None'. This will set the orientation of the joint to it's parent.

c000be
11-21-2008, 08:10 AM
thank YOU!! your orient joint tool suggestion works great.
now i just have to figure out why iK spline handle tool never seems to work for me. i do exactly as said in the directions in the pdf file, books, etc.. and nadda.

and if anyone haven't checked out imdb.com for tv shows and movies you can watch, lately, enjoy. it's also a great resource for all info movies and television. it's all there.

Keithtron
11-21-2008, 04:46 PM
When I'm building my skeletons, I first get my joint placement correct without worrying too much about orientation. Once the template skeleton is built and I'm happy with all the joint placements, I create a new skeleton by vertex snapping new joints to the template skeleton. That ensures that the parent joint is always pointed towards its child.

For the end joint orientations, it sorta depends on what your end joints are. I just build extra joints into my skeleton, then delete them once the skeleton is built. For example, I place joints at the very tips of the fingers, so when you build your skeleton the first knuckle points straight at the finger tip. Then once I'm finished with the skeleton, I just delete the finger tip joints. (I do the same thing with extra toe joints, a top-of-the-head joint, and front-of-mouth jaw joint as well.) This ensures that your end joints are pointed in the right direction, without having to do any extra playing around with them. You could always leave those extra end joints in and not delete them, but I prefer to not have any more influences in my rig than necessary, just to keep it as clean and simple as possible.

For the wrist joint orientations, I prefer to have it pointing straight out from the arm rather than toward a finger. An easy way to do that is to make a copy of your elbow joint, and snap it to the wrist position, and use that as your new wrist joint.

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