POV-Ray : Newsgroups : povray.binaries.animations : left or right handed rotations Server Time: 18 Jun 2019 06:37:35 GMT
 left or right handed rotations (Message 1 to 8 of 8)
 From: omniverse Subject: left or right handed rotations Date: 7 Oct 2016 19:15:01 Message:
```After reading about this at:

http://news.povray.org/povray.documentation.inbuilt/message/%3Cweb.57f3be98a39309ab21263ef70%40news.povray.org%3E/#%3Cw
eb.57f3be98a39309ab21263ef70%40news.povray.org%3E

I had to get another look for myself at what happens when changing viewpoint for
+z. Found the x and y rotations appear opposite, yet z remains counterclockwise
when seen from these different directions and with the change to x sign.

First is the usual view for many POV-Ray scenes with camera at a -z coordinate,
looking toward +z. The default 'up' +y and 'right' +x (or <4/3,0,0>).
```

Attachments:

 From: omniverse Subject: Re: left or right handed rotations Date: 7 Oct 2016 19:20:01 Message:
```"omniverse" <omn### [at] charternet> wrote:
>
>
http://news.povray.org/povray.documentation.inbuilt/message/%3Cweb.57f3be98a39309ab21263ef70%40news.povray.org%3E/#%3
Cw
> eb.57f3be98a39309ab21263ef70%40news.povray.org%3E
>
> I had to get another look for myself at what happens when changing viewpoint for
> +z. Found the x and y rotations appear opposite, yet z remains counterclockwise
> when seen from these different directions and with the change to x sign.
>
> First is the usual view for many POV-Ray scenes with camera at a -z coordinate,
> looking toward +z. The default 'up' +y and 'right' +x (or <4/3,0,0>).

Second is with negative 'right', or right <-4/3,0,0>, and 'up' still positive y.
```

Attachments:

 From: clipka Subject: Re: left or right handed rotations Date: 7 Oct 2016 20:02:01 Message: <57f7ff39\$1@news.povray.org>
```Am 07.10.2016 um 21:18 schrieb omniverse:
> "omniverse" <omn### [at] charternet> wrote:
>>
>>
http://news.povray.org/povray.documentation.inbuilt/message/%3Cweb.57f3be98a39309ab21263ef70%40news.povray.org%3E/#%3
> Cw
>> eb.57f3be98a39309ab21263ef70%40news.povray.org%3E
>>
>> I had to get another look for myself at what happens when changing viewpoint for
>> +z. Found the x and y rotations appear opposite, yet z remains counterclockwise
>> when seen from these different directions and with the change to x sign.
>>
>> First is the usual view for many POV-Ray scenes with camera at a -z coordinate,
>> looking toward +z. The default 'up' +y and 'right' +x (or <4/3,0,0>).
>
> Second is with negative 'right', or right <-4/3,0,0>, and 'up' still positive y.

The reason why rotation about Z /appears/ to remain the same is that
from the camera's point of view it /appears/ like you've achieved the
change in handedness (which flips all rotations) by flipping the Z axis
(which additionally flips the rotation around the Z axis); so
effectively you've flipped the apparent rotation about the X and Y axes
once, and the rotation about the Z axis twice making it the only
rotation that appears unchanged.

If you chose the opposite camera perspective for the 2nd video, you
could achieve that the Y and Z axes appear to remain the same and the X
axis appears to be flipped; in that case, the rotation about the Y and Z
axes would appear to be flipped, and the rotation about the X axis would
appear to remain unaffected.

Likewise, you should also be able to make it appear as if rotation about
the Y axis remained unaffected but the other two flipped, or to make
rotation about all three axes to appear flipped.

I haven't thought it through entirely yet, but I suspect it is
impossible to flip the handedness while making rotations about an odd
number of axes appear unaffected.
```
 From: omniverse Subject: Re: left or right handed rotations Date: 8 Oct 2016 04:50:01 Message:
```clipka <ano### [at] anonymousorg> wrote:
> Am 07.10.2016 um 21:18 schrieb omniverse:
>
> --->8---
> I haven't thought it through entirely yet, but I suspect it is
> impossible to flip the handedness while making rotations about an odd
> number of axes appear unaffected.

You're talking to someone who can't follow directions very well, so all that
only confused me more. Sorry! :) I began to understand and then got lost!

You did give me an idea though, and that was to try placing a mirror behind the
rotating box to see what happens. I would never be able to visualize it without
the animations.

Found out the mirrors show the opposite handedness, left looks like right in the
mirror and right looks left-handed. Of course the axes must be used in the
mirrors too, doing the hand aerobics from them and not the axes from original
non-mirrored versions.

Will also post those here along with my test scene text, just in case anyone
wants to mess with it more and not have to start with a blank slate.

1st the left-handed with right-hand mirror (hope I'm seeing these as such
anyhow).
```

Attachments:

 From: omniverse Subject: Re: left or right handed rotations Date: 8 Oct 2016 05:20:01 Message:
```// cmd:+w320 +h240 +fj +a0.1 +ki0 +kf1 +kfi1 +kff150

#version 3.7;

global_settings
{
assumed_gamma 1
ambient_light 0
}

#local LR=0; // 0 for left-handed, 1 or any number for right

light_source
{
<11,11,-11>, 1
}

camera
{
#if (LR=0)
location <6,8,-10>
right <4/3,0,0>
#else
location <6,8,10>
right <-4/3,0,0>
#end
up <0,1,0>
look_at <0.5,1.75,0>
angle 60
}

#if (LR=0)
plane
{
-z,-7
texture
{
pigment
{
rgb 0
}
finish
{
reflection 1
}
}
//no_image
}

#else

plane
{
z,-7
texture
{
pigment
{
rgb 0
}
finish
{
reflection 1
}
}
}

#end

// room grid
box
{
<-12,-12,-12>*0.99,<12,12,12>*0.99
texture
{
pigment
{
function {abs(x)}
color_map
{
[0.15 rgb <1,0,0>]
[0.15 rgb <1,1,1>]
}
}
finish
{
emission 0.1 diffuse 0.6
}
}
texture
{
pigment
{
function {abs(y)}
color_map
{
[0.15 rgb <0,1,0>]
[0.15 rgbt <1,1,1,1>]
}
}
finish
{
emission 0.1 diffuse 0.6
}
}
texture
{
pigment
{
function {abs(z)}
color_map
{
[0.15 rgb <0,0,1>]
[0.15 rgbt <1,1,1,1>]
}
}
finish
{
emission 0.1 diffuse 0.6
}
}
}

// axis center
sphere
{
0,0.5
texture
{
pigment
{
rgb 0.1
}
finish
{
emission 0.1 diffuse 0.6
specular 0.5 roughness 0.05
}
}
}

#declare Axis=
union
{
cylinder
{
-x*3,x*3,0.25
texture
{
pigment
{
color_map
{
[0.5 rgb <0,1,1>]
[0.5 rgb <0.5,0.5,0.5>]
}
}
finish
{
emission 0.1 diffuse 0.6
specular 0.25 roughness 0.1
}
}
}
cone
{
x*3,0.33,x*4,0
texture
{
pigment
{
rgb 0.75
}
finish
{
emission 0.1 diffuse 0.6
specular 0.25 roughness 0.1
}
}
}
}

object
{
Axis
}

object
{
Axis
rotate <0,0,90>
}

object
{
Axis
rotate <0,-90,0>
}

// rotating box
box
{
-1,1
texture
{
pigment
{
checker rgbt <1,1,0,0.5> rgbt <1,0,1,0.5>
}
finish
{
emission 0.1 diffuse 0.6
specular 0.5 roughness 0.01
}
}
scale 2
//translate -z*5
#if (clock<0.333)
rotate <3*clock*360,0,0>
#local Xd=1; #local Yd=0.3; #local Zd=0.3;
#else
#if (clock<0.667)
rotate <0,3*clock*360,0>
#local Xd=0.3; #local Yd=1; #local Zd=0.3;
#else
rotate <0,0,3*clock*360>
#local Xd=0.3; #local Yd=0.3; #local Zd=1;
#end
#end
}

text
{
ttf "arialbd"
"X",0.2,0
texture
{
pigment
{
red 1
}
finish
{
emission 0.1 diffuse Xd
specular 0.5 roughness 0.05
}
}
translate <4.5,-0.25,0>
}

text
{
ttf "arialbd"
"Y",0.2,0
texture
{
pigment
{
green 1
}
finish
{
emission 0.1 diffuse Yd
specular 0.5 roughness 0.05
}
}
translate <-0.25,4.5,0>
}

text
{
ttf "arialbd"
"Z",0.2,0
texture
{
pigment
{
blue 1
}
finish
{
emission 0.1 diffuse Zd
specular 0.5 roughness 0.05
}
}
translate <-0.25,-0.25,4.5>
}
```

Attachments:

 From: Bald Eagle Subject: Re: left or right handed rotations Date: 10 Oct 2016 16:10:00 Message:
```"omniverse" <omn### [at] charternet> wrote:

> Found out the mirrors show the opposite handedness, left looks like right in the
> mirror and right looks left-handed.

This is to be expected - I've had to deal with lots of diagrams of chemical
enantiomers and showing the R/S, (+)/(-), D/L chiral configuration of the
central carbon atom.

Mirror images always have reversed chirality - both geometrically and
rotationally.

I'd put a reference rotational arrow around your axes to show what the default
direction for positive rotation is.

http://www.f-lohmueller.de/pov_tut/trans/trans_200e.htm
```
 From: omniverse Subject: Re: left or right handed rotations Date: 10 Oct 2016 19:55:01 Message:
```"Bald Eagle" <cre### [at] netscapenet> wrote:
> I'd put a reference rotational arrow around your axes to show what the default
> direction for positive rotation is.
>
> http://www.f-lohmueller.de/pov_tut/trans/trans_200e.htm

Yep, I always need reminders for how things work like Vectors and
Transformations that Friedrich shows.

Taking your suggestion I remade my still small and sloppy animation with +
rotation arrows.
```

Attachments:

 From: Mike Horvath Subject: Re: left or right handed rotations Date: 21 Nov 2016 18:53:56 Message: <583342c4@news.povray.org>
```You should upload that movie to Wikipedia to use in this article:

https://en.wikipedia.org/wiki/Orientation_(vector_space)

Mike
```