Re: axis of rotation :: again

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Scott McMillan (scott++at++ht.com)
Thu, 15 May 1997 12:55:46 -0400 (EDT)

>
> Well I gess I was not too clear:
>
> I tryed Scott's idea with no result and Angus wants more info..
>
> I have a model with multiple parts which I wish to rotate (say legs and
> arms) I am able to rotate each part alone but they all rotate about the
> same point (0,0,0) of the model. What I wish to do is move this point
> of rotation to another location like the hips or shorlders.
>
> I hope this is more clear... Thanks for the help....

Lemme try again (and be a little more public). This is what I have done in
the past with robotic sims where the point of rotation for a particular model
will always be in the same place with respect to that model. I believe it is
equivalent to some of the single DCS answers I have seen.

I strive for the following subgraph (for each link in the system), by
inserting an SCS:

        DCS (joint axis - variable)
|
        SCS (offset to point of rotation - constant)
|
       Model (Geode,Geosets,etc)

....later if I want to make it more efficient, I can pfFlatten or ask the 3D
modelers to give me a new model with the origin moved to the point of
rotation.

For example if you want the point of rotation to be about 1,1,1 of the models
coordinate system. The SCS's matrix will consist of a translation of
-1,-1,-1 (I hope, I dont have that backwards).

I have to align my models so that the single axis of rotation is about the
z-axis so I generally have to have some rotation in my SCS matrix to align
this correctly. If I can do it, I will always have the modeller create the
models with the origin and orientation in the place I need it so that I do
not have to go through this process.

Hope this helps,
scott

-- 
  Scott McMillan  |    HT Medical, Inc.   | Developing medical VE's
   scott++at++ht.com   |   http://www.ht.com   | surgical simulations
 Ph: 301-984-3706 |6001 Montrose Rd., #902| and surgery simulation
Fax: 301-984-2104 |  Rockville, MD 20852  | creation tools.


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