PDA

View Full Version : Joint Rotation Order


safakoner
07-30-2005, 05:29 PM
hi

I watch the Hyper Realistic Body Setup.
The lecturer said. "positive Z rotation for the joint should be facing forward".
Is it realy important? I use generally XYZ like world. I haven't a problem with this. I just want to ask.
thanks

john_homer
07-31-2005, 02:45 AM
Is it realy important?

no.
Use what you like unless you are exporting to something with limitations, (like mocap) although they would generally be the down axis rather than the other 2...

.j

bakwudz
08-01-2005, 04:25 PM
are we talking about left-handed vs right-handed coordinate systems or joint rotations orders? Or maybe world vs model vs bone space? Different things really. Joint rotation order would be the order in which you apply pitch, heading, roll(bank). Determining the whether positive Z goes into or out of your monitor is a coordinate system issue. Spaces are basically what frame of reference your rot/trans are happening in. +Z in model space maybe a different direction than +Z in world space.

I find the coordinate system a non-issue. Like john_homer said, unless you are exporting geometry and importing into other apps or a game, you don't really have to worry about it. You can even export as-is from maya and let your target app handle the flip.

Joint rotation order is a huge issue for me. I'm writing rigging and animation scripts that are never used outside of maya and the results i get are highly dependent on selection order of rotations inside the DAG.

Spaces are a little bit more complicated and may or may not be an issue depending on if you referencing different objects in the scene in relation to each other. i'm not familiar with the video you reference but sounds he is just basically telling you to line up model space with world space to make expressions or calculations easier (avoiding the matrix multiplies). the only time i can see this screwing you is when you rotate the model and your script assume the model space axis is still equivalent to the world space axis. if you aren't doing anything this complicated in script or whatever, take john_homer's advice and forget about it.

john_homer
08-01-2005, 08:39 PM
I'm not sure where " coordinate systems" came into this... the subject is joint rotation order...

and sure its important to be consistant between your rigs/scenes and scripts, but the question was.. is it true that "positive Z rotation for the joint should be facing forward".

and the answer is no, that was just a choice the tutotial writer made for that tutorial, and wanted the student to do it that way so it worked for the rest of the tutorial. and I'm sure any scripts in the tutorial would then expect the joint to be z forward.

.j

bakwudz
08-01-2005, 08:52 PM
I'm not sure where " coordinate systems" came into this... the subject is joint rotation order...
.j

because he was looking for an answer about coordinate systems/spaces not whether heading is applied before pitch or after bank.

john_homer
08-01-2005, 08:58 PM
because he was looking for an answer about coordinate systems/spaces not whether heading is applied before pitch or after bank.

really? are you sure?

anyway, I'm sure the question has been answered...

.j

safakoner
08-05-2005, 08:27 AM
thanks all
I got the answer :thumbsup:

Octagon
08-05-2005, 10:53 AM
I'm not sure where " coordinate systems" came into this... the subject is joint rotation order...

and sure its important to be consistant between your rigs/scenes and scripts, but the question was.. is it true that "positive Z rotation for the joint should be facing forward".

and the answer is no, that was just a choice the tutotial writer made for that tutorial, and wanted the student to do it that way so it worked for the rest of the tutorial. and I'm sure any scripts in the tutorial would then expect the joint to be z forward.

.j

Actually the very name of this thread (rotation order) is misleading because what Paul Thuriot (I think) meant in the video didn't have anything to do with rotation orders whatsoever.
It has of course technically but the whole gimbal lock issue was not at all his point. He merely advisied that it's favorable to work out a convention -together with animation- as to how in general axes should be setup. He came up with the idea of pointing z along global z, so that increasing values would bring knees, elbows and spine etc. "forwards". This is sensable but it's not a requirement at all for a working rig. But it does help animation a lot especially when tweaking stuff in the graph editor.

my 2 cents
Matthias

pthuriot
08-06-2005, 03:43 AM
octagon is correct.

it is NOT needed...but it's advisable to come up with a convention of some kind (for everything really--not just joint directions, etc.) between the setup and the animation departments, to minimize any "learning curves" of any rig.

CGTalk Moderation
08-06-2005, 03:43 AM
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.