POV-Ray : Newsgroups : povray.documentation.inbuilt : Lathe and Prism updates requested by Christoph. : Re: Lathe and Prism updates requested by Christoph. Server Time
17 May 2022 19:39:39 EDT (-0400)
  Re: Lathe and Prism updates requested by Christoph.  
From: Le Forgeron
Date: 3 Jun 2016 22:47:02
Message: <57524126$1@news.povray.org>
Le 03/06/2016 23:51, William F Pokorny a écrit :
> On 06/03/2016 02:24 PM, clipka wrote:
>> Am 27.05.2016 um 02:11 schrieb William F Pokorny:
>>
>> It might be worth actually testing how the clockwise/counter-clockwise
>> thing works out depending on the handedness of the coordinate system,
>> rather than just speculating or relying on unconfirmed assumptions.
>>
> 
> I assume you mean flipping the handedness of the camera to right and looking at all
the test cases I created?
> 
> It is true I ran only one of the tests posted to povray github this way(1). It
didn't change result with 3D handedness. It will take me some time to crank all the
test cases with a right hand camera & review the results.


The result might be the same (actually, it should be so, as the coding of the object
remains identical), but changing the handedness, for the *same* code of the object, is
also changing the notion/visualisation of clockwise/counter-clockwise.

Put coloured spheres at the various points used on object, using H of HSV or HSL
colour coding as the progression along the points.
One handedness would display a clockwise progression, and the other handedness the
counter-clockwise progression.
(you could use text item, but text would need to be oriented to be readable, less
problem with coloured spheres)


> 
> Is there some case you suspect will flip for the 2D curves that I might jump to
first in an attempt to save some time? You're usually a few steps (as in gigantic,
flying leaps) ahead of me... :-)
> 
> End of a long day, but I'm still thinking 2D is 2D & while given rotations and
mirroring things might at first look different given a viewpoint, there is really only
one normal planar 2D representation.
> 
> (1)- (bezier, lathe, 12 counter-clockwise loops varying point set rotations,
straddling y=0 forming rings about y)
> 
>>
> ...
>>> So, I guess the question is do we:
>>>
> ...
>>
>> - Keep the "clockwise" and "counter-clockwise" wording, and add a note
>> saying that these apply to POV-Ray's left-handed coordinate system,
>> whereas with a right-handed coordinate system the direction is reverse?
>>
>> (Of course such a note should only be added if tests show that it is
>> indeed the case ;))
>>
> 
> I will check in on this thread tomorrow morning, before running what test cases I
have with a right hand camera set up.
> 
> Bill P.


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