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Author Topic: Issue with Sequence Editor - Rotating Bones  (Read 4494 times)

hf003

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Issue with Sequence Editor - Rotating Bones
« on: January 27, 2010, 02:21:05 am »

I am not sure if this is by design or not. When a bone is rotated about the Pink Axis, the Green Axis does not track with the bone’s position (I used Front view and middle button to move the bone). The Blue axis tracks, so both Blue and Green Axis can have coincidental planes. I would expect both Axis to move along with its bone axis for which it belongs to. This issue makes it very difficult (impossible?) to implement restricted bone movements properly. Also, When I rotate about the Blue Axis, neither the Pink or Green axis track their corresponding bone’s axis. Only rotations around the Green Axis results in the expected behavior. Issue exists at least in V95c and V97d.
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Raxx

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Re: Issue with Sequence Editor - Rotating Bones
« Reply #1 on: January 27, 2010, 03:54:24 am »

Answered several times. Just search the forum.

http://www.anim8or.com/smf/index.php?topic=518.msg3259#msg3259
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hf003

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Re: Issue with Sequence Editor - Rotating Bones
« Reply #2 on: January 28, 2010, 10:10:00 pm »

Hi Raxx, thanks for your reply.

Unfortunately, the link you gave me does not address the issue I am seeing with the Sequence editor.

I have no problem getting the bones to rotate in any direction I want. However, when I rotate the bones using the "Middle" mouse button" to rotate about the "Z" Axis, the X-Axis does not rotate about the "Z" Axis along with the bone, while the Y-Axis does. If I rotate exactly 90 degrees, then both X-Axis and Y-Axis are in the same plane. I do not think it should do this, as now it is impossible to rotate the bone using the "Left" mouse button in any direction other than what can be done with the "Right" mouse button. The X-Axis should rotate 90 degrees as well (imo).

Here are the steps to reproduce the issue.

1. In Figure Mode: Add one bone to the root bone.
2. In Figure Mode: In "front" view, rotate the bone 90 degrees so it sits horizontal.
3. In Figure Mode: Remove all movement restrictions for that bone.
4. In Sequence Mode: Load the figure and "Show Axis"
5. In Sequence Mode: In "front" view rotate the bone 90 degrees so it is pointing strait down (or strait up) using the "Middle" mouse button.
6. In Sequence Mode: Go to to "Left view".
7. In Sequence Mode: Try to rotate the bone using the "Left" mouse button - Nothing happens.
8. In Sequence Mode: Go to "Ortho" view try to rotate the bone using the "Left" mouse button. - You get the same rotation as using the "Right" mouse button. This is because the X-Axis and Y-Axis are coincidentally in the same plane.

Also, when I rotate about the "Y" Axis, neither the X-Axis or Z-Axis move, as such the limits on these axis do not rotate along with the bone.
 
To be clear, when I mentioned X-Axis, Y-Axis, and Z-Axis above, I meant the colored Axis that we see when we use "Show Axis", while "X" Axis, "Y"Axis, and "Z" Axis denote the non-changing screen coordinates. The issue is that the colored Axis do not stay coincidental with their corresponding Bone's Axis when the bone is rotated about the "Z" and "Y" Axis.

Again, this is not what I would expect. Please try it, maybe there is a reason for this behavior I am not aware of.

There is also another issue where "Undo" does not undo bone rotations (V97d). It just deselects the bone. But that is not so bad.
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hihosilver

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johnar

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Re: Issue with Sequence Editor - Rotating Bones
« Reply #4 on: January 29, 2010, 12:30:40 pm »

 Hello hf003,

I'm not sure whether this is 'by design or not', and don't know myself whether eulers rotation theorem explains or not, that this is how it should be.
  (nice links hiho. Can't watch them on my connection, but definately will when i get a chance).

 hf003.  I followed your instructions, and wonder whether the problem is the normal 'gimbal lock', which sounds as though it is an expected problem when working with euler rotations. ? i don't really know for sure, but i do have a workaround that i thought might be worth mentioning, in case you haven't already thought of it.
 With character animation in anim8or,  this problem is always in the 'upper arm'.
 ie: in front view, character has arms out straight. If i bend the upper arm down, Z axis, and then try to move the arm fwd, x axis, then thats when you get a problem. (as you have explained, very well. ;) )
 So, my way around that is to do the x axis rotations FIRST.
 It takes a bit of thinking/planning ahead, but it gets the job done and, for me anyway, i'm noticing the improvements in my character animation, becoz i can now get the arms to move more freely and easilly than i could when i was struggling with exactly the thing which you are talking about.
 
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hf003

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Re: Issue with Sequence Editor - Rotating Bones
« Reply #5 on: January 29, 2010, 09:39:17 pm »

Thanks much hihosilver,

That explains the issue very well. As johnar pointed out, it is exactly the Gimbal Lock" problem that I ran into here. I see most problems with "Gimbal Lock" can be avoided by choosing the correct axis hierarchy. I am assuming that can be done by rotating the bones in the Figure Editor first to get the correct hierarchy that best suits one's needs. I'll try what johnar suggested.
Thanks all
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hf003

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Re: Issue with Sequence Editor - Rotating Bones
« Reply #6 on: March 05, 2010, 05:36:27 pm »

After playing around with this a bit, I realized Gimbal Lock does not occur in the Figure editor. Both Sequence and Figure Editor allow bone rotation, yet Gimbal lock is only a problem in the Sequence editor. Although, I did not do an extensive test, I now believe it is impossible to avoid Gimbal Lock when animating all possible movements of a human's arms in the Sequence editor. If I am wrong, can someone please create a tutorial showing how to do such?

 
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hihosilver

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Re: Issue with Sequence Editor - Rotating Bones
« Reply #7 on: March 05, 2010, 06:30:10 pm »

You don't run into Gimbal lock in figure mode because you're not animating the bones.  You're simply moving them to where you want them to begin, so there is no issue.  There isn't necessarily a way to avoid Gimbal lock altogether, but there are definitely ways to get around it.  I don't have specific methods but I believe other members do (I believe they add an extra bone in the arm or shoulder.)
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