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Thread: Quick, easy discussion: What seems to be the standard orientation/joint direction.

  1. #1
    variable srlake314's Avatar
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    Default Quick, easy discussion: What seems to be the standard orientation/joint direction.



    Good day/evening!

    I was wondering and I know there are a lot of different ways of doing things. The topic? Not joint orientation as far as XYZ, ZYX or YXZ or any other combo ;), but rather which direction the axis's point.

    1) I learned X always pointing "down" the chain(or up if going up the spine), however, after that, I didn't really "learn" the rest per se'.
    2) Y pointing outwards from the spine(pointing in the -zed axis) or Y pointing in the +zed axis?
    3) If it (Y) points towards the back of the back(-zed), should it be pointing up or down on the foot's position joints?

    Just curious what the standard, would be for the first point and the other questions are more technical than choice, as they would be directly impacted if properly oriented :).

    Thanks!

    Just wanted a discussion possibly to help others with this basic, yet tricky concept if not paid attention to.

    Also, if folks from gaming to animation studios could put their 2 cents in about "their" company standards that would be great :).!

    Have a happy holiday!

  2. #2
    program Theodox's Avatar
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    I'ts all a convention: as long as you know what you're trying to accomplish, the labels 'x' , 'y' and 'z' don't matter much in themselves.

    The important thing to remember is that the precision of the local angles is dependent on the rotation order. You want the 'twist' axis of a joint chain to be the first euler rotation axis -- if you want to build along X then use the XYZ or XZY order, if you want to build along Y use YZX or YXZ, and so on. Typically your order should be 'twist', 'thing that rotates the least', 'thing that rotates the most'. The middle rotate term is the one that is likeliest to cause gimbal issues or to generate euler flipping when constrained.

    This video shows the likely effects https://vimeo.com/54541692

    Individual studios will often split on whether or not their output supports negative bones scales. If you're working in a game engine that doesn't support negative scales you need to be more creative in mirroring your settings than just using Maya's 'mirror behavior' setting.

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    variable srlake314's Avatar
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    Quote Originally Posted by Theodox View Post
    I'ts all a convention: as long as you know what you're trying to accomplish, the labels 'x' , 'y' and 'z' don't matter much in themselves.

    The important thing to remember is that the precision of the local angles is dependent on the rotation order. You want the 'twist' axis of a joint chain to be the first euler rotation axis -- if you want to build along X then use the XYZ or XZY order, if you want to build along Y use YZX or YXZ, and so on. Typically your order should be 'twist', 'thing that rotates the least', 'thing that rotates the most'. The middle rotate term is the one that is likeliest to cause gimbal issues or to generate euler flipping when constrained.

    This video shows the likely effects https://vimeo.com/54541692

    Individual studios will often split on whether or not their output supports negative bones scales. If you're working in a game engine that doesn't support negative scales you need to be more creative in mirroring your settings than just using Maya's 'mirror behavior' setting.
    You're awesome! Thanks. Yeah, I was thinking of the different studios that I hear do Z down the chain as opposed to X, but yeah, all just a matter of preference I guess :0).

    Thanks!

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    variable srlake314's Avatar
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    Default Update added question :).

    Quote Originally Posted by srlake314 View Post
    You're awesome! Thanks. Yeah, I was thinking of the different studios that I hear do Z down the chain as opposed to X, but yeah, all just a matter of preference I guess :0).

    Thanks!
    Now when you were referring to, "middle rotate term", in the first case XYZ, Y would be the culprit, I presume. Now what do you mean by the last statement, "...or to generate euler flipping when constrained" are you referring to when a constraint(orient for example) is placed on it by the controller curve created for the animator?

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    program Theodox's Avatar
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    For a given movement in 3d space, the middle rotation term (the Y in xyz, the Z in yzx, etc) is the one whose values will be the most unpredictable. If you build a simple 2 or 3 bone chain in any orientation, animate it with IK and constraints and then bake it back to FK keys you'll see that the second Euler term is the likeliest to have big swings in value.

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    variable srlake314's Avatar
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    Awesome! thanks Theodox! I appreciate it. It totally makes sense.

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