noob: joint orientation

[Sammy]

... the simplest way to describe what Joint orientation is - is that you're editing the LOCAL rotation axis of the joint. I assume you know the difference between LOCAL and WORLD axis. Joint orientation is one of the first theories related to quality character rigs.

When you first create joints, Maya will GUESS the best direction for the local axis - but this is rarely good enough, and is often WAY off. For instance - fingers ... you rotate your index finger and the TIP of your finger will curl into the first joint of the forefinger ...

... but often, when you first set up your hand joint the finger joints might each have an inperfect joint orientation - and the result is that they curl off at an odd angle - the forefinger curls into your MIDDLE finger's first joint - or heaven forbid, you're PINKY's first joint ... all of which is just plain wrong.

So you finesse the joint rotations so that it rotates as you'd expect.

The second reason is related more towards the graph editor. It's best to have all your joints follow the same rotation convention. Selecting a bunch of joints that have NOT been oriented and rotating them along Y -- they'll all rotate at strange angles ... when they all should really only rotate along their centers.

I prefer to have Y going down bone - as usually when describe to anyone that something is rotating around it's center people assume you mean the Y axis. Whether Z is UP/OUT or X is UP/OUT is up to you.

If Y is shooting down bone then you'll usually decide to have the Z or X axis shoot out at 90degress from that.

Z-up or Z-down, X-up or X-down relates to when you, for instance, rotate in +Z, the joint curls forwards and when you rotate in -Z it rotates backwards ... you could also choose to have it rotate side to side.

If you choose to use Z for side to side or back and forth isn't TOO too important, but the IMPORTANT part is to BE CONSISTENT. Establish a few rules for yourself in the beginning and apply that to each joint. For instance, selecting the left and right wrists and rotating in +Z should create the same result ... boths wrists should rotate DOWN.

or use a little common sense and use the positive=forward rule ... but in the end it's up to you -- or in the case of a studio, it's up to them.

So this is why you go into component mode and rotate the local axis until you get it perfect.
It's a VITAL part of creating a good rig.

With all that said it can be a big brain drain doing this by hand. And if you do it all by hand you'll usually have to go into the joint a few times and perfect it as you're doing it by eye. Thankfully there are scripts that get you 98% of the way there. Jason Schleifer of WETA fame has released his orientation script that does a terrific job.

http://jonhandhisdog.com

look in the downloads section - it's called jsOrient

... hope that helps clarify a few things for you.

Cheers,
Sammy

[mimo8]

hi sammy,

thnx a million for taking so much time to give me an insight into this topic.
I hope many other people searching for a introduction on joint orientation may find it via search function.

I am not totaly new to maya and rigging so I allready knwo abbout the existens and necessity of joint orientation, having worked through steven tubbrits rigging tutorial I also allready uses the jsOrient.mel

but I never exactly knew why ... now I do :thumbsup:
seems that it is all abbout the handling of the character while animating it so it hasd to be understandable, predictable and consistent ... as you allready said.

just to add some of my little knowledge:
quoting what I read in other posts it is very necessary for joints that are animated via FK, but when they are constrainted or using IK it is not important cause you dont deal with their orientation anymore, but just with the translation data of the controllers they follow ... correct me if I am wrong

thnx aggain

[Sammy]

... yeah, that's right - with IK you don't have to worry about joint orientations. Mind you, if you're switching between FK and IK like on the arms then you need to orientate -- at least the FK part of your FK/IK switched rig ... for obvious reasons.

I'm glad my post helped answer some of your questions ...

cheers,
Sammy

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