Is there a specific reason why POV-ray uses a left-handed coordinate
system?

-- 
Kaveh

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Kaveh <kav### [at] delete_thisfocalimagecom> wrote:
> Is there a specific reason why POV-ray uses a left-handed coordinate
> system?

  For 90% of people it's easier to write with the right hand while they
do axis visualizations with their left hand.

-- 
#macro M(A,N,D,L)plane{-z,-9pigment{mandel L*9translate N color_map{[0rgb x]
[1rgb 9]}scale<D,D*3D>*1e3}rotate y*A*8}#end M(-3<1.206434.28623>70,7)M(
-1<.7438.1795>1,20)M(1<.77595.13699>30,20)M(3<.75923.07145>80,99)// - Warp -

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Warp <war### [at] tagpovrayorg> wrote:

> Kaveh <kav### [at] delete_thisfocalimagecom> wrote:
> > Is there a specific reason why POV-ray uses a left-handed coordinate
> > system?
> 
>   For 90% of people it's easier to write with the right hand while they
> do axis visualizations with their left hand.

Is this really the reason? So has everyone else got it wrong, e.g.
maths, physics, etc?

-- 
Kaveh

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Kaveh <kav### [at] delete_thisfocalimagecom> wrote:
> Is this really the reason?

  No, it was humor.

-- 
#macro M(A,N,D,L)plane{-z,-9pigment{mandel L*9translate N color_map{[0rgb x]
[1rgb 9]}scale<D,D*3D>*1e3}rotate y*A*8}#end M(-3<1.206434.28623>70,7)M(
-1<.7438.1795>1,20)M(1<.77595.13699>30,20)M(3<.75923.07145>80,99)// - Warp -

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On Fri, 15 Nov 2002 12:41:45 +0530, kav### [at] delete_thisfocalimagecom
(Kaveh) wrote:

>Is there a specific reason why POV-ray uses a left-handed coordinate
>system?

Left-handed people have, on average, an IQ about 5 points higher than
the average for right-handed people. That's the reason that the
POV-Team has in its long history *only* accepted left-handed people in
its ranks. The only right-handed person in there is Lutz Kretzschmar
(author of Moray) and they've been trying to get rid of him for years,
but after the hit squad took down the wrong guy for the 11th time
because Chris Cason *again* misspelled Lutz's name, they gave it up
and let him go on with his heresy for the sake of the POV community
(the last one of false victims was, by mishap, a volunteer who taught
POV in a community school in Zaire).

How do I know? Well, being a TAG member, I have certain privileges.
Though after what I just disclosed, you might not hear from me
anymore...





Tongue *so* deep in the cheek it almost comes out of the ear :)


Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] vipbg
TAG      e-mail : pet### [at] tagpovrayorg

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In article <1flp1lf.b3ye8bmkt22oN%kaveh@delete_this.focalimage.com>,
 kav### [at] delete_thisfocalimagecom (Kaveh) wrote:

> Is this really the reason? So has everyone else got it wrong, e.g.
> maths, physics, etc?

In screen coordinates, x is usually from left to right, and y from 
bottom to top. The left handed coordinate system is simply an extension 
of this: z going into the screen. It is not something unique to POV, it 
is used in many other places as well.
Even in right handed coordinate systems, the y axis is often "up" 
(OpenGL for example). The difference is that the z axis points out of 
the monitor instead of into it. A depth buffer is often called a 
"z-buffer", but never a "y-buffer". I think the main source of the "z is 
up" system is actually architectural drawings, it makes sense when x and 
y are already used for a horizontal plane on paper. In math, I often see 
the z coordinate visualized as depth into a graph instead of height.

Neither way is "wrong", they are just different conventions. An analogy 
would be row-major vs. column-major matrices.

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/

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If this is too inconvenient, you can always modify your camera
statement, as referenced in:
http://www.povray.org/documentation/view/28/  
--LibraryMan

Kaveh wrote:
> 
> Is there a specific reason why POV-ray uses a left-handed coordinate
> system?
> 
> --
> Kaveh

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More specifically,
http://www.povray.org/documentation/view/339/

--MMW

LibraryMan wrote:
> 
> If this is too inconvenient, you can always modify your camera
> statement, as referenced in:
> http://www.povray.org/documentation/view/28/
> --LibraryMan
> 
> Kaveh wrote:
> >
> > Is there a specific reason why POV-ray uses a left-handed coordinate
> > system?
> >
> > --
> > Kaveh

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LibraryMan <mrm### [at] attnet> wrote:

> If this is too inconvenient, you can always modify your camera
> statement, as referenced in:
> http://www.povray.org/documentation/view/28/  
> --LibraryMan

No, doesn't worry me at all. Just that I studied physics, and was used
to right handed systems. Thanks for link anyway.

> 
> Kaveh wrote:
> > 
> > Is there a specific reason why POV-ray uses a left-handed coordinate
> > system?
> > 
> > --
> > Kaveh


-- 
Kaveh

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By the way, when calculating handedness-related things literally
using your hand as an aid, it's very important to remember that
the thum is *always* the x-axis (and the next fingers are the y and
the z axes).
  I once saw a site which explained the handedness in the wrong way.
IIRC it had the middle finger as x and the thumb as z. This completely
reverses the whole concept. If you do it this way, all rotations will
be reversed (you can't use your hand to visualize the direction of the
rotation in a given coordinate system because it will be reversed).

  (If you didn't know, you can easily visualize which direction does
a positive angle rotate an object by pointing your thumb (of the left
hand if you are using the left-handed coordinates) towards the positive
axis around which you are rotating and bend your fingers.)

-- 
#macro M(A,N,D,L)plane{-z,-9pigment{mandel L*9translate N color_map{[0rgb x]
[1rgb 9]}scale<D,D*3D>*1e3}rotate y*A*8}#end M(-3<1.206434.28623>70,7)M(
-1<.7438.1795>1,20)M(1<.77595.13699>30,20)M(3<.75923.07145>80,99)// - Warp -

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