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View Full Version : pivot points, centers, bounding box question


tredeger
05-11-2007, 04:41 AM
I'm terribly confused about how maya is determining the bounding box of my objects. My expectation is that the bounding box should basically be the smallest box lined up with the world axes that completely holds an objects verts (in a poly mesh for example). If the object has a pivot point that is not "inside" the area of the verts, I can imagine a bounding box that would be calculated to include the pivot. What I don't get are bounding boxes that are nowhere near the points that make up the visible geometry. And it seems very very easy to end up with such situations.

Case 1: imported a mesh object in .OBJ format. It was very large so I scaled all three axes to 0.175. Now the bounding box is below the object. I never moved the pivot or anything else. Grrrr.


Case 2: More complicated, I created a nurbs circle which I wanted to use and shape as a control curve on my rig. Translated it to a general position, then moved CVs to shape it more precisely. Snapped the pivot point to a bone.

The bone was oriented arbitrarily (not along a world axis) and I wanted the curve's orientation to match. I wanted to be able to zero the values on the control curve while maintaining orientation, so I grouped the curve to itself. The center of the group is the world origin of course. So I moved the pivot point of the group to the same place as the bone and the control curve. They all share the same pivot point now. Behavior works as expected when i use this to set up neutral poses for control curves.

Now i proceed with rigging my joint chains and control curves and all seems fine will i select a curve and try to frame selection in the viewport. I zooms WAYYYY out. Eventually I set the view to bounding box and discover that for some of my curves the bounding box is at the world orgin (even though the pivot for the group has been moved) and that for some of my curves the bounding box is in some crazy place with a crazy location (as the group to which is corresponds has been nested in some hierarchy and is inheriting transforms.


So, while the rig is behaving well enough, the frame selection is completely frelled. Is there a way to address this problem that isn't completely kludgey? I suppose the kludgey solution would be to create everything with the pivot at the origin, create the group while it is still there and then move it in to place by moving the group.

But this totally defeats the point of being able to just hit insert to move the pivot point. I guess the behavior makes sense if moving the pivot point is just putting a transformation on the object rather than moving its true center. But then the question is how do i move the true center so that it is in the same place as the pivot? I tried deleting history but that didn't work. Freezing transformations did not work either. That just looses the orientations that were the whole point to begin with. Also, this hacked solution would require that I tear apart a whole tonne of work on objects that are already wired up with parenting and constraint relationships.

Thanks in advance for any wisdom and help. Take care and

cheers,
jazz

tbaypaul
05-15-2007, 05:45 PM
are you actually getting the bounding box from the xform command?......or are you relying on the frame selection hot key "f ".......frame selection seems to be buggy....in my case I thought it was some non-visibile display layers....I thought this because it stops zooming out uncontrollably when the layers are visible and behaves fine after that.....I think you are confusing data with opengl issues.....but it is hard to tell as your post is far too long....

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05-15-2007, 05:45 PM
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