Re: Channel view hpr settings

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Don Hatch (hatch++at++hell.engr.sgi.com)
Fri, 5 Feb 1999 17:05:03 -0800

On Feb 5, 12:56pm, Scott Herod wrote:
> Subject: Channel view hpr settings
> I realize that rotation matrices don't commute,
> but I am a little surprised that heading changes
> and roll changes are negatives of each other if I
> pitch down by 90 degrees. Try

The alternative is that they are negatives of each other when you
pitch *up* by 90 degrees... would that be less surprising?

> Is this typical behavior in 3D systems?

Doesn't Performer define what is typical? :-)

But seriously, there is a nice consistency
resulting from the choice of signs to be such that
the primitive rotations h,p,r take +x to +y,
+y to +z, and +z to +x respectively.
That makes it possible for me to actually get the directions right
without having to consult a book each time (but maybe I'm just weird).
I suspect most 3D systems do this.

Don

-- 
Don Hatch  hatch++at++sgi.com  (650) 933-5150  Silicon Graphics, Inc.

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