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astronomy calculations, and they are all right handed.
If not, could such a setting be added to POVRay? Thanks.
Mike
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On 2292018 7:41, Mike Horvath wrote:
> Is there a way to change the handedness of a scene? I am doing a lot of
> astronomy calculations, and they are all right handed.
>
> If not, could such a setting be added to POVRay? Thanks.
>
There are different types of 'handedness' depending on which way the
different axis point. For Moray, which had z up and x right, the
following transform was used:
transform {
scale <1, 1, 1>
rotate x*90
}
Could be used from POV>Moray or from Moray>POV.
You may have to experiment because in some cases/applications the x or
the z axis can point the other way round. For instance, in Silo (which
is lefthanded) the z axis points out of the screen. The same kind of
things may apply to righthanded applications I guess.

Thomas
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Am 22.09.2018 um 07:41 schrieb Mike Horvath:
> Is there a way to change the handedness of a scene? I am doing a lot of
> astronomy calculations, and they are all right handed.
In POVRay, handedness is defined by the camera. The defaults
right x*1.33
up y
direction z
or, in v3.8.0
right x*image_width/image_height
up y
direction z
result in a lefthanded coordinate system. For a righthanded coordinate
system, you have to set one (or all three) of these vectors to the
opposite direction, e.g.:
direction z
Note that this works even if you override the actual directions by using
`look_at`.
Note that this also has an effect on textures; you may need to mirror
planet image maps (e.g. using `scale <1,1,1>` in the image map) to get
correct results.
> If not, could such a setting be added to POVRay? Thanks.
I intend to add an explicit "handedness" parameter to the global
settings, for more intuitive switching, including a change in the
behaviour of UV mapping and image map projection types. But it'll be a
while until I get around to that.
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On 22/09/2018 06:41, Mike Horvath wrote:
> Is there a way to change the handedness of a scene? I am doing a lot of
> astronomy calculations, and they are all right handed.
>
You could put all that Matrix maths in the Bezierpatch torus thread to use.
http://www.techart3d.com/2016/02/convertlefthandedtorighthandedcoordinates/
> If not, could such a setting be added to POVRay? Thanks.
>
>
It was good to read clipka's reply. :)

Regards
Stephen
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On 9/22/2018 2:41 AM, Thomas de Groot wrote:
> On 2292018 7:41, Mike Horvath wrote:
>> Is there a way to change the handedness of a scene? I am doing a lot
>> of astronomy calculations, and they are all right handed.
>>
>> If not, could such a setting be added to POVRay? Thanks.
>>
>
> There are different types of 'handedness' depending on which way the
> different axis point. For Moray, which had z up and x right, the
> following transform was used:
>
> transform {
> Â scale <1, 1, 1>
> Â rotate x*90
> }
>
> Could be used from POV>Moray or from Moray>POV.
>
> You may have to experiment because in some cases/applications the x or
> the z axis can point the other way round. For instance, in Silo (which
> is lefthanded) the z axis points out of the screen. The same kind of
> things may apply to righthanded applications I guess.
>
The problem is that I'd have to do this *each time* I define an object
or perform a transform. Whereas a single keyword at the start of a scene
or in an INI file would be without worry.
Mike
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On 9/22/2018 4:01 AM, clipka wrote:
> I intend to add an explicit "handedness" parameter to the global
> settings, for more intuitive switching, including a change in the
> behaviour of UV mapping and image map projection types. But it'll be a
> while until I get around to that.
>
Okay thanks.
Mike
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On 9/22/2018 4:27 AM, Stephen wrote:
> On 22/09/2018 06:41, Mike Horvath wrote:
>> Is there a way to change the handedness of a scene? I am doing a lot
>> of astronomy calculations, and they are all right handed.
>>
>
> You could put all that Matrix maths in the Bezierpatch torus thread to
> use.
>
> http://www.techart3d.com/2016/02/convertlefthandedtorighthandedcoordinates/
>
What would I need to do for astronomy maths? In the equations I am using
the Z and Y axes are switched.
Also, how do I multiply matrix transforms in POVRay?
Mike
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On 9/22/2018 6:36 AM, Mike Horvath wrote:
> On 9/22/2018 4:27 AM, Stephen wrote:
>> On 22/09/2018 06:41, Mike Horvath wrote:
>>> Is there a way to change the handedness of a scene? I am doing a lot
>>> of astronomy calculations, and they are all right handed.
>>>
>>
>> You could put all that Matrix maths in the Bezierpatch torus thread
>> to use.
>>
>> http://www.techart3d.com/2016/02/convertlefthandedtorighthandedcoordinates/
>>
>
> What would I need to do for astronomy maths? In the equations I am using
> the Z and Y axes are switched.
>
> Also, how do I multiply matrix transforms in POVRay?
>
>
> Mike
The directions of rotations also seem reversed.
Mike
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On 22/09/2018 11:36, Mike Horvath wrote:
> On 9/22/2018 4:27 AM, Stephen wrote:
>> On 22/09/2018 06:41, Mike Horvath wrote:
>>> Is there a way to change the handedness of a scene? I am doing a lot
>>> of astronomy calculations, and they are all right handed.
>>>
>>
>> You could put all that Matrix maths in the Bezierpatch torus thread
>> to use.
>>
>> http://www.techart3d.com/2016/02/convertlefthandedtorighthandedcoordinates/
>>
>
> What would I need to do for astronomy maths? In the equations I am using
> the Z and Y axes are switched.
>
> Also, how do I multiply matrix transforms in POVRay?
>
>
I might be able to help from a practical view. Blender uses the Yup
coord system.
Here is the output of a uv mapped mesh2 sphere, declared as DATASphere
object {
DATASphere
matrix <1.000000, 0.000000, 0.000000, 0.000000, 0.000000,
1.000000, 0.000000, 1.000000, 0.000000, 0.000000, 0.000000, 0.000000>
}
But you would either have to transform them individually or put them in
a union and transform that.

Regards
Stephen
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On 22/09/2018 16:22, Mike Horvath wrote:
> On 9/22/2018 6:36 AM, Mike Horvath wrote:
>> On 9/22/2018 4:27 AM, Stephen wrote:
>>> On 22/09/2018 06:41, Mike Horvath wrote:
>>>> Is there a way to change the handedness of a scene? I am doing a lot
>>>> of astronomy calculations, and they are all right handed.
>>>>
>>>
>>> You could put all that Matrix maths in the Bezierpatch torus thread
>>> to use.
>>>
>>> http://www.techart3d.com/2016/02/convertlefthandedtorighthandedcoordinates/
>>>
>>
>> What would I need to do for astronomy maths? In the equations I am
>> using the Z and Y axes are switched.
>>
>> Also, how do I multiply matrix transforms in POVRay?
>>
>>
>> Mike
>
> The directions of rotations also seem reversed.
>
>
Not unexpected. That sounds like handiness. Try scale 1 * x

Regards
Stephen
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