Re: [Xvrml-agents] on animation

[Miriam E. <mi...@we...>]

Just thinking further on this...

If you make force an attribute of other geometry, be aware that more than one attribute is needed to provide all the force info.

- the direction and intensity (just occurred to me it can be a single vector)
- the point at which it is applied to the object (default to center of mass?)

There is no need to specify rotation because ODE would handle that from the force angle, position, and offset from center of mass or IK linkages.

That just made me realise that specifying mass alone is not enough. Center of mass is needed too. It would not necessarily be the geometric center of the object.

Further thoughts?

Best wishes,

	- Miriam


Miriam English wrote:

> 
> 
> Jeff Sonstein wrote:
> 
>> On Jun 28, 2005, at 11:22 PM, Miriam English wrote:
> 
> 
>> so you would suggest "Force" as a grouping node?
>>
>> what about adding (optional attributes with zeros for default values)
>> to the grouping nodes themselves?
>> this would eliminate adding node(s) to the spec
> 
> 
> When I originally thought about this some time back I was torn between 
> making it an attribute or a separate node that was connected to the 
> things it acted upon via something like routes (though I'd favor direct 
> coupling rather like the IS in PROTOs).
> 
> The reason I suggested a grouping node for force is that I got to 
> thinking more about it and realised that a grouping node would let you 
> put it around all the geometry in a file to act as gravity, or a large 
> part of a scene to act as a wind, or several objects to act as magnetism.
> 
> I'm still not convinced any of the 3 alternatives is right. Will making 
> a force attribute be restrictive or inefficient? You can activate a 
> force attribute on several objects simultaneously and achieve the same 
> effect as a grouping force, but it requires a lot more explicit 
> coding... unless the force attribute could be an attribute of existing 
> grouping nodes. On the other hand orchestrating a series of actions by a 
> single force (imagine one of those leaf blower machines being waved 
> around to clear a footpath of leaves) would be very difficult 
> (impossible?) to program using grouping nodes, and would be best done 
> via attributes.
> 
> OK. You've convinced me. :)
> Force should be an attribute, but not only of geometry, it should also 
> be an attribute of grouping nodes.
> 
> Best wishes,
> 
>     - Miriam
> 

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