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From: thant@horus.sgi.com (Thant Tessman)
Newsgroups: comp.sys.sgi
Subject: Re: subroutines perpec and lookat
Summary: lookat command
Message-ID: <39166@sgi.SGI.COM>
Date: 28 Jul 89 22:44:06 GMT
References: <8907250331.AA20644@prism.gatech.edu> <38766@sgi.SGI.COM> <39135@sgi.SGI.COM>
Sender: daemon@sgi.SGI.COM
Organization: Silicon Graphics, Inc., Mountain View, CA
Lines: 33

In article <39135@sgi.SGI.COM>, tarolli@dragon.wpd.sgi.com (Gary Tarolli) writes:
> In article <38766@sgi.SGI.COM>, thant@horus.sgi.com (Thant Tessman) writes:
> > In article <8907250331.AA20644@prism.gatech.edu>, ccsupos%prism@GATECH.EDU ("SCHREIBER, O. A.") writes:
> > 
> > 
> > This is probably due you assuming that z is up (a perfectly reasonable
> > assumption, one would think) but that the 'lookat' for historical reasons 
> > thinks that y is up, not z.
> > 
> > 
> 
> I think it is perfectly reasonable for y to be the up axis.  Its not a 
> historical reason, its a logical one.  If z was up, then zbuffers would
> be called ybuffers wouldn't they?   Zbuffers are called zbuffers because
> the z axis runs along the line of sight!  This implies x and y are 
> therefore up/down  and right/left.
> --
> 						Gary Tarolli
> 
> 

These are exactly the historical reasons I was refering to.  It's logical
to computer scientists who started out having to address pixels on a 
screen using x and y.  (Zbuffers are called zbuffers because X and Y were
taken already.)  Unfortunately for computer scientists, the 
rest of the world thinks z is up.  If we were building these things just 
for computer scientists it would have also had a left handed coordinate 
system (gods be praised it doesn't).

Seriously, the hotline has spent a man-century or two trying to explain
why the 'twist' never seems to do what people thought it did.

thant@sgi.com