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.

> 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.

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clipka <ano### [at] anonymousorg> wrote:

>
> 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.

Egads, then +Z becomes -Z in POV-Ray!  :-O

But you're right, of course.

My own concept of the axes (putting aside what I learned in school) is kind of
an odd one--or maybe not so odd?  I've been sketching things all my life
(mechanical stuff mostly, in semi-perspective views), and 'right' is +x
naturally, but z is *mostly* INTO the page, and y is *mostly* up, but kind of
sticking OUT of the page a little. (Similar to an isometric view when drafting,
but not as extreme.) Maybe this is why POV's left-handed system was such an easy
learn for me.

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Am 01.03.2013 07:08, schrieb Kenneth:
> My own concept of the axes (putting aside what I learned in school) is kind of
> an odd one--or maybe not so odd?  I've been sketching things all my life
> (mechanical stuff mostly, in semi-perspective views), and 'right' is +x
> naturally, but z is *mostly* INTO the page, and y is *mostly* up, but kind of
> sticking OUT of the page a little. (Similar to an isometric view when drafting,
> but not as extreme.) Maybe this is why POV's left-handed system was such an easy
> learn for me.
Well, that depends on how we start a plan and how we continue.
Starting with the front view:
   x right, y up. The house behind the front goes to +z = left-handed.
Starting with the top view on ground plan:
  x right front line, y = depth, so z = up seems okay! = right-handed.

Interesting the different positions in the last 4 contributions here!
So all positions are justified - except those, who want to
declare a type of system as 'natural' and 'absolutely correct'!

Her in Germany, some regions, by 'orders from above', have decided that
their teachers at school must use a right-handed system.
And teachers, who use POV-Ray at school, are often confronted with
big resistances, because 'it is using a wrong system of coordinates'.
The students themselves do not have so much trouble with it.
  :-)

Friedrich

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> 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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Am 01.03.2013 22:42, schrieb Alain:

>> 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...

That's a left-handed system indeed, but I doubt it's the standard used 
in professional mathematics and physics. (Then again, in professional 
mathematics the handedness of the world is just abstracted away anyway. 
That leaves physics though.)


> 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.

If you swap any of the two components, you can do the same stunt with 
the right hand.

But here are two stunts you can't do left-handed:

Make a "thumbs-up" sign with your right hand. Point your thumb in the 
direction of current in a wire. The fingers will curl in the direction 
of the magnetic field around the wire.

Make a "thumbs-up" sign with your right hand. Hold your hand so that the 
fingers curl in the direction of current flowing in a coil. The thumb 
will point in the direction of the magnetic field inside the coil.


> 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 true in both left- and right-handed coordinate systems, simply 
due to the way positive rotation is defined. (In other words, in a 
left-handed coordinate system positive rotation is defined just the 
other way round as in a right-handed one.)


> 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.

It might be a UK-schools special, which would explain why POV-Ray uses 
it. (Then again, you are not from the UK, are you?)


>> 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.

Doing the gymnastics again, yes - it is indeed.

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> Am 01.03.2013 22:42, schrieb Alain:

>>> 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...
>
> That's a left-handed system indeed, but I doubt it's the standard used
> in professional mathematics and physics. (Then again, in professional
> mathematics the handedness of the world is just abstracted away anyway.
> That leaves physics though.)
>
>
>> 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.
>
> If you swap any of the two components, you can do the same stunt with
> the right hand.
>
> But here are two stunts you can't do left-handed:
>
> Make a "thumbs-up" sign with your right hand. Point your thumb in the
> direction of current in a wire. The fingers will curl in the direction
> of the magnetic field around the wire.
>
> Make a "thumbs-up" sign with your right hand. Hold your hand so that the
> fingers curl in the direction of current flowing in a coil. The thumb
> will point in the direction of the magnetic field inside the coil.
>
>
>> 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 true in both left- and right-handed coordinate systems, simply
> due to the way positive rotation is defined. (In other words, in a
> left-handed coordinate system positive rotation is defined just the
> other way round as in a right-handed one.)
>
>
>> 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.
>
> It might be a UK-schools special, which would explain why POV-Ray uses
> it. (Then again, you are not from the UK, are you?)
No. Canada.
>
>
>>> 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.
>
> Doing the gymnastics again, yes - it is indeed.
>

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On 1-3-2013 22:42, Alain wrote:
> Using the right hand, it require you to twist your arm to have the thumb
> point toward +X, then the index point to +Z
>

Just as an info: The modeller Silo uses the following right-handed 
system coordinate:

X to the right (thumb)
Y up (index)
Z towards viewer/out of screen (middle)

Moray, on the other hand (no pun intended), was right-handed as follows:

X to the right (thumb)
Y towards screen (index)
Z up (middle)

Thomas

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Thomas de Groot <tho### [at] degrootorg> wrote:

>
> Just as an info: The modeller Silo uses the following right-handed
> system coordinate:
>
> X to the right (thumb)
> Y up (index)
> Z towards viewer/out of screen (middle)
>
> Moray, on the other hand (no pun intended), was right-handed as follows:
>
> X to the right (thumb)
> Y towards screen (index)
> Z up (middle)
>

What a mess! :-P

Well, there seems to be at least ONE 'standard' that everyone/every system
agrees on: +x is to the right. Hooray! It's good to know that there's one little
'island of stability' in a chaotic world. ;-)

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On 6-3-2013 9:15, Kenneth wrote:
> What a mess! :-P
>
> Well, there seems to be at least ONE 'standard' that everyone/every system
> agrees on: +x is to the right. Hooray! It's good to know that there's one little
> 'island of stability' in a chaotic world. ;-)

In fact, once you get used to manipulating the different systems at the 
same time, you know exactly what to expect and how to merge everything 
harmoniously into POV-Ray.

So, for Moray, I always had two lines of code ready whenever I imported 
a Moray object into a POV scene:

scale <1,1,-1>
rotate <90,0,0>

Except of course, when I used complete Moray scenes. I suppose that the 
/new/ future Moray version is going to be left-handed by the way ;-)

Using Silo, I model as if the object were left-handed, export it as 
left-handed through Poseray, and then just rotate it by 180*y whence in 
POV-Ray.

Little tricks, but becoming automatic.

Thomas

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Am 06.03.2013 09:15, schrieb Kenneth:
> Thomas de Groot <tho### [at] degrootorg> wrote:
>
>>
>> Just as an info: The modeller Silo uses the following right-handed
>> system coordinate:
>>
>> X to the right (thumb)
>> Y up (index)
>> Z towards viewer/out of screen (middle)
>>
>> Moray, on the other hand (no pun intended), was right-handed as follows:
>>
>> X to the right (thumb)
>> Y towards screen (index)
>> Z up (middle)
>>
>
> What a mess! :-P
>
> Well, there seems to be at least ONE 'standard' that everyone/every system
> agrees on: +x is to the right. Hooray! It's good to know that there's one little
> 'island of stability' in a chaotic world. ;-)
>
I don't want not spoil your joy :-)
but "+x is right" is not always right!
Sometimes it's also left!
Take a look at http://www.f-lohmueller.de/pov_anim/ani_3920d.htm

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