Problem about parent-and-child~

[actarus1]

hi everyone~
Here is a scene, a cube place at (0,6,0) and then a null object place at (0,0,0). then make the null object as the parent of cube. then i select the null ONLY and rotate it, the child (i.e. cube in this case) will not rotate about the null, even if i press R to refresh the screen. but if i select null object only and then set a rotation animation to it, while in playback, the cube will rotate about the null object, why???? If i really want to make the cube can rotate about the null object outside animation mode, I need to select the whole branch (i.e. both null and cube) and then rotate it, why would this happen?? I can't find out what's going on about that..........
thanks~

[pomme]

yes, i find that this is very stupid. however, it just works that way, is the setup of this program.

[devdoka]

When you manipulate objects, only the selected elements and their relations are affected. The reason the cube doesn't move until you set keyframes on it is because you haven't established a relationship prior.

When an object is keyframed by position, orientation, or scale, it's values are relative to it's parent. If the object does not have a parent, then the values are relative to the world origin. This applies to all objects except 2D/3D skeleton chain effectors which always use global coordinates by default.

If you change the order of the steps you listed, you'll get different results to illustrate the workings:

1) Get a null and cube and put them in the same place as before.

2) Select the cube and set a translation keyframe.

3) Select only the null and rotate it. Notice the cube follows because it's trying to maintain the relationship between it's keyframed values and it's parent - the null.

4) Select the cube. Motion > FcrvReset > Object > all.

5) Select the null and rotate it. Notice the cube no longer follows.

In SI3D, objects don't move unless they've established a relationship with some other element in the scene. Once a relationship is established, everybody plays follow the leader. When you select objects in branch mode, you establish a temporary relationship that tells all the children to follow the parent object. When the objects are deselected, the realtionship is destroyed and behaviour returns to the pre-selected state.

Hope this helps,

Matt

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Matt Lind
Animator / Technical Director
Softimage certified instructor:
Softimage|3D
Softimage|XSI
speye_21@hotmail.com