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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On 06/03/2016 10:46 PM, Le_Forgeron wrote:
> Le 03/06/2016 23:51, William F Pokorny a écrit :
>>
>> 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.
>

Indeed there was no change in inside vs outside determination for any 
test case using a right handed camera set up.

> 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)
>
>

See:

http://news.povray.org/povray.binaries.images/thread/%3C5752dc4c%40news.povray.org%3E/

The viewer's perception due left versus right handed camera set ups does 
of course changes for the prism due the point set being described in the 
x,z plane, but not for the lathe due in being describe in the x,y plane.

One could say for the case of the prism, in moving to the right handed 
camera - while not changing any other scene set up - we have decided to 
look at the 2d clock face upside down. ;-)

Anyway, I understand the concern. Guess it comes to whether the wording 
Jim added in :

Note: The use of clockwise and counter-clockwise in the following 
examples should not be taken imply any notion of handedness.

enough to address it or do we need to add something more?

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On 05/26/2016 08:03 PM, Jim Holsenback wrote:
> On 5/25/2016 6:53 PM, Jim Holsenback wrote:
>> On 5/24/2016 9:32 AM, William F Pokorny wrote:
>>> Would someone who knows what they are doing wiki-wise - or who has the
>>> "create" authority for the reference->object->lathe/prism sections can
>>> create the talk/discussion area. Or, I suppose, if the update looks good
>>> to those reviewing, just get it into the actual reference.
>>
>> lathe additions have been added:
>> http://wiki.povray.org/content/Reference:Lathe
>>
>> didn't have time to do prism yet
>
> prism additions have been added:
> http://wiki.povray.org/content/Reference:Prism ... thanks for the
> contribution
>
Jim,

Another version of both lathe and prism documentation is available at:

http://wiki.povray.org/content/User:Wfpokorny

Thanks.

Bill P.

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On 6/6/2016 7:32 AM, William F Pokorny wrote:
> Another version of both lathe and prism documentation is available at:
>
> http://wiki.povray.org/content/User:Wfpokorny

LOL semantics ... updated.

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