> There is no global transformation data. It all depends on how the model
> is structured, which depends on the exporter used. I would assume most
> systems to have a transformation node close to the root to move the
> whole object around, but it is just as valid to have no transformations
> at all and change all the object coordinate to move objects around.


Ok, I got it thanks

> But if I understand your problem right (grabbing objects and moving them
> around) you don't need absolute transformation anyway, all you need is
> the relative transformation from the hand/pointer to the object at the
> time the object is grabbed. You can get that by multiplying the
> transformation of the hand to world with the inverse transformation from
> the object to world. Then when the hand transformation changes, you
> multiply it with that stored matrix and you get a new transformation to
> apply to the object.

Wow, I suppose that this is the solution to most of
my troubles, but I cannot get it very well.
Naming Mh the matrix that rapresents the hand in world
space, and Mobj the matrix that rapresents the object
picked in world space in the moment of picking
I suppose from what you told me to save
Msave=Mh*inv(Mobj)
in the moment of picking and to compute the new position
of the object as Mhn*Msave where Mhn is the new position
of the hand. Well, I tried those formulas but It doesn't
work, cause I get random position when I picked something
Maybe I missed something but I want to have understood
the math. Shouldn't the relative position be
Msave=inv(Mh)*Mobj???
Thanks a lot for your help and sorry for my poor math

Esimio prof. Antonio Lioy

>
> Hope it helps
>
>       Dirk
>
>
>
>
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