Re: [Algorithms] How to derive transformation matrices

[Klaus H. <k_h...@os...>]

----- Original Message -----
From: Steve Wood <Ste...@im...>
To: <gda...@li...>
Sent: Tuesday, July 25, 2000 11:10 PM
Subject: RE: [Algorithms] How to derive transformation matrices


> Yes, a "shear plane" describes the plane where two surfaces move by each
> other.  A force causing these surfaces to move is called a shear force and
> is parallel to the shear plane,

I agree here.

> however it is perpendicular to the surface
> of contact.

With this I don't agree. Certainly, in the case of your box, the shear force
is perpendicular to the surface of contact. But that's not necessarily true
for other primitives. What about spheres for example? Imagine a sphere that
is centered at the origin. The fixed plane is the x/z plane of the world
coordinate system, and we shear along the x-axis (y, and z are fixed). So
our shear force could be represented as a vector H = <h 0 0>, where h is the
magnitude of the force in x-direction. Would you still say, that the shear
force if perpendicular to the surface of contact? Maybe I just misunderstand
you, but for me it's not perpendicular to the surface of contact.

> A dictionary sometimes doesn't provide what you might learn in
> an engineering textbook.

Yeah, forget that dictionary thing. I don't even know why I posted this :(

> But, again I don't think the original poster (OP) has an object box
breaking
> apart and just wants to deform it, like turning a box into a trapezoid

I think that's a parallelepiped, but I'm not 100% sure.

But you are right... this really doesn't help the OP author. So I'll just
exit the thread here, unless I decide to provide something more useful.

Niki