Re: shape rotation

On Tuesday, August 26, 2003, at 07:44  PM, Rick Giuly wrote:

> Suppose I want to make something like a flower with rectangular prisms 
> for
> petals.
>
> Top view of four petals:
>
>   |
> -   -
>   |
>
>
> Say I want 10 petals, and I want them arranged and 36 degree spacing 
> (rather
> that the 4 petals at 90 degree spacing shown in the figure).
>
> I suppose I could do that by making each petal a Mobile with a box 
> shape (shape
> init-with-cube...). The Mobile class would provide the rotation and 
> translation
> to arrange the petals. But say I want all the petals hinged together.
>
> I think that would mean the petals could not be Mobile's, they would 
> need to be
> Link's. Link's have no rotate/move accessor, so I don't know how I 
> would rotate
> and move them into place.

The short answer: look at the Joint class for the set-relative-rotation 
and
set-relative-rotation-matrix methods.

Explanation: As you're seeing, Link objects are not rotated using 
explicit
rotation methods the way Mobile objects are.  This is because the Link 
object
is not an independent physical object--it has to be connected to other 
Links
via joints, and ultimately associated with a MultiBody.

It is the positions and rotations of the Joint objects which control the
relationship between links, not any settings in the Link itself.

Hope this helps!

- jon

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