[help-3dldf] Rotations

[Laurence Finston]

I've "cc"-ed `help-3dldf', because I'd like to have this in the archive
(and so there's at least a little traffic on it).
You may get a message from the list server if you reply.

> 
> I think that some graphics experts must know how to fix those alignment
> problems, and why double's does not seem to be enough for you. 

It's enough for practical use, but it bothers me.  I haven't found anything
about this in the graphics books I've looked at.  I haven't yet gotten to the
point of researching recent articles rather than monographs.  The research in
3D graphics has gotten quite specialized whereas I'm still implementing basic
functionality in 3DLDF. 

(Is it
> something wrong with the precision on your computer; has double precision
> (64-bit) trigonometry functions for some reason by mistake been replaced by
> single precision floats (32-bit)?)
> 

No, I don't think so.  I originally programmed 3DLDF on a 64-bit machine (a
DEC Alpha) and then ported it to a 32-bit one.  The problem was already
present in the original version.  

Laurence

-------------------
> >> If you work directly with matrices, rotations are described by the
> >> orthogonal matrices A, i.e., satisfying A*A^tr = 1. (This is essentially
> >> what quaternions do in three dimensions.) One can describe them using
> >> trigonometry.
> >
> >Thanks for the hints.  I'll look into this more when I get back to working
on
> >this part of my program.
>