> Am 01.03.2013 04:14, schrieb Alain:

>>
>> In my math classes when looking at geometry, we only used the
>> left-handed coordinate and rotation system. Also, Y was always UP and Z
>> forward, NEVER relative to the paper's surface.
>>
>> It was the same in my physics courses.
>
> What? For us it was /always/ right-handed, for both maths and physics. I
> can't believe it's different across the world in such disciplines.
>
> ... unless of course you use a different scheme to assign axes to the
> fingers. We used thumb=X, index=Y, and middle=Z.

Using the right hand, it require you to twist your arm to have the thumb 
point toward +X, then the index point to +Z

In my courses, with the left hand, it was: thumb = +Y, index= +Z, 
middle= +X with the index pointing forward and the thumb up.
Very easy to hold, and you can still have a pen in your right hand...
Maybe just a coincidence, but it's the same thing that is used to get 
the direction of the force exerced on a conductor in a magnetic field. 
The index is in the direction of the current (positive), the thumb in 
the direction of the magnetic field (north pole), and the middle finger 
in the direction of the force.
For the rotations, you point the thumb toward the + side of an axis, and 
the fingers curl in the direction of the positive rotation.

That's why, for me, ther was no learning curve to use the POV-Ray 
coordinate system. It's exactly the same I always used in school.

>
>> The right-handed system is mostly used by architecs, and, as most early
>> modeling applications where made for architecs, it stuck. It's also why
>> we have the infamous Z for the up direction. Architecs use the X and Y
>> axis along the ground and on paper where +X is right and +Y is the top
>> of the paper.
>
> If you put a proper math-style 2D coordinate system (X axis right, Y
> axis "top") onto paper, and then add +Z as height above ground, that's a
> left-handed system to me.
>
That's exactly how architecs work. And that's right handed.



Alain

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