Re: Left-handed vs. right-handed

I haven't explained myself very well, so let me try to be more specific.

In my way of thinking I have to change neither my code nor my data.
What I do have to change is the _representation_ of my data.  My world
has a bunch of vectors and transformations in it.  Mathematically
speaking, these do not start life with an intrinsic coordinate
representation---it's only once you've picked a coordinate frame that
you can evaluate basis functions and write down some numbers.  It's
worth remembering that you've made a choice and done some work here.
(The fact that they're called Cartesian coordinates should help you
remember that once upon a time this was not a trivial idea.)

Unfortunately, computers are good at numbers and bad at abstraction,
which means that to do anything useful at all you have to pick a basis
before you start.  This is a Bad Thing.  Typically, picking a basis is
the last thing you want to do---ask anyone who's had to write down a
bunch of proofs in linear algebra.

Now, my contention is that at run-time you want to avoid having to deal
with reflections: SO(3) is much nicer than O(3).  Given that
requirement, the assumptions implicit in whatever driver/API is
underneath may make your choice of basis for you.  This is fine---just
transform the representation of your data and away you go.  Everything
will still work---clockwise is still clockwise since it's well-defined
in your world, independently of the coordinate representation.

The key is to make all your own code basis-agnostic.  This is easy if
you have no preference!

Graham



-----Original Message-----
From: Alen Ladavac [mailto:[email protected]] 
Sent: 06 May 2009 12:32
To: Graham Hazel
Cc: Game Development Algorithms
Subject: Re: [Algorithms] Left-handed vs. right-handed

Graham wrote at 5/6/2009:
> Since it's clearly "correct" to be agnostic, I prefer to work with
> the chirality that the graphics driver expects.

Which one of the driver multitude of possible drivers and APIs? Even
if you are single-platform-single-API and if you adapt everything to
"The One API" you use now, few years from now you may have to adapt
the same codebase to a different platform/API. I'd bet you are safer
sticking to the winding (or chirality, call it all you want) that
_you_ prefer, and be prepared to convert signs and windings on every
interfacing point with any external API. It's not _that_ much of a
hassle, as long as you are clear on what you use internally.

JM2C,
Alen


------------------------------------------------------------------------------
The NEW KODAK i700 Series Scanners deliver under ANY circumstances! Your
production scanning environment may not be a perfect world - but thanks to
Kodak, there's a perfect scanner to get the job done! With the NEW KODAK i700
Series Scanner you'll get full speed at 300 dpi even with all image 
processing features enabled. http://p.sf.net/sfu/kodak-com
_______________________________________________
GDAlgorithms-list mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/gdalgorithms-list
Archives:
http://sourceforge.net/mailarchive/forum.php?forum_name=gdalgorithms-list