Hello

Please help me to find some details about Cylindrical projection.

Thanks.

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"Hamed Ahmadi" <h.a### [at] hotmailcom> wrote in message 
news:web.472766c1f915cc94f104cee20@news.povray.org...
> Hello
>
> Please help me to find some details about Cylindrical projection.
>
> Thanks.
>

Hi Hamed,

There's a 'cylinder' camera type that you can find in the POV-Ray help file 
by searching for 'cylindrical projection' in the index. There are a few 
types of projection described there and the 'panoramic' camera type also 
gives a form of cylindrical projection.

Also it's possible to project an image (or any other pigment) onto a 
cylinder (or indeed onto any other object) using a cylindrical warp. Look 
for 'cylindrical warp' in the help where there's an example of using the 
cylindrical warp to project a hexagonal pigment onto a cylinder.

Hope that helps. Otherwise, are you able to be a bit more precise about what 
you're trying to do?

Regards,
Chris B.

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Thanks for your answer,

actually i'm going to render some 3d models on a cylindrical screen with a
projector and i don't know how to reduce the distotion.
so i'm searching for a way to preduce a distorted screen that looks undistorted
on the cylindrical screen. Could you help me please?

Thanks in advance.

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web.4729d5115849c6ccf104cee20@news.povray.org...
> Thanks for your answer,
>
> actually i'm going to render some 3d models on a cylindrical screen with a
> projector and i don't know how to reduce the distotion.
> so i'm searching for a way to preduce a distorted screen that looks 
> undistorted
> on the cylindrical screen. Could you help me please?
>
> Thanks in advance.
>
you could try a cylindrical camera as below.
As you see the scene is very simple : a 1/2 cylinder with a radial pattern.
rendered through a cylindrical camera placed on the axis, the pattern 
appears as evenly wide bands.
Is that what you want?

Marc (code below)

#version 3.5;



global_settings {
  assumed_gamma 1.0


}
background { color rgb <0.1, 0.3, 0.8> }

// ----------------------------------------


#declare Cylindrical_projection=1;//Set this value to  1 to render a 
cylindrical projection
#if (Cylindrical_projection)
// cylinder lens for axis distorted field of view
// 1 is vertical cylinder, fixed viewpoint
// 2 is horizontal cylinder, fixed viewpoint
// 3 is vertical cylinder, viewpoint moves along the cylinder's axis
// 4 is horizontal cylinder, viewpoint moves along the cylinder's axis
camera {
  cylinder 1            // types 1, 2 ,3, 4
  location <0,0,0>     // position
  right x*5             // horizontal aspect or field of view
  up y*2                // vertical aspect or field of view
  look_at  <0,0,1>      // view
  angle 181
}

#else

// perspective (default) camera
camera {
  location  <2.0, 2.0, -2.0>
  look_at   <0.0, 0.0,  0.0>
  right     x*image_width/image_height
}
#end


light_source {
  <0, 0, 0>            // light's position (translated below)
  color rgb <1, 1, 1>  // light's color
  translate <-10, 30, -30>
}



// ----------------------------------------



#declare Bandes= pigment{
radial frequency 10
color_map {
  //  [ END_VAL color red R green G blue B filter F transmit T]
  [ 0.5  color rgb 0]

  [ .5  color rgb 1 ]
  // (---alternative form---)
  //[ 1.0  color rgbf <0.8, 0.8, 0.8, 1.0> ]
} // color_map
}

intersection{
cylinder{-y,y*1.1,1 texture{ pigment{Bandes}finish {ambient 0 diffuse 0.6}}}
box{<-1,-1.1,0>,<1,1,1> pigment {color rgbt 1}}
no_shadow}

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Hello

as i said before i wanna use a projector and show the scene on a real
cylindrical screen, so i have a question. If i do that with the settings
you mentioned in the previous post, the scene on the screen won't be distorted?

Thanks.

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web.472acbd45849c6ccf104cee20@news.povray.org...
> Hello
>
> as i said before i wanna use a projector and show the scene on a real
> cylindrical screen, so i have a question. If i do that with the settings
> you mentioned in the previous post, the scene on the screen won't be 
> distorted?
>
> Thanks.
>
It depends on the lense you use.
May  we have some details on the technics involved in this projection?

Marc

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> It depends on the lense you use.
> May  we have some details on the technics involved in this projection?
>
> Marc

Dear Marc

I don't have any special technic and i just wanna find a way to have
a undistorted scene on a cylindrical screen with a ordinary projector.
of course I prefer to do that by software modification not by hardware
for example i guess there should be a matrix if i used it in my code (directx)
i will have a undistorted scene, but hardware ways may be used too.
Do you know a special lens for that?

Regards,
Hamed.

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web.472ad84c5849c6ccf104cee20@news.povray.org...
> Dear Marc
>
> I don't have any special technic and i just wanna find a way to have
> a undistorted scene on a cylindrical screen with a ordinary projector.
> of course I prefer to do that by software modification not by hardware
> for example i guess there should be a matrix if i used it in my code 
> (directx)
> i will have a undistorted scene, but hardware ways may be used too.
> Do you know a special lens for that?
>
> Regards,
> Hamed.
>
Err I must admit that's beyond my knowledge

Marc

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Thanks anyway,

If you find something even a little, please let me know
you know, i am crazy about the subject.

Best wishes,
Hamed.

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Hash: SHA1

Hamed Ahmadi wrote:
>> It depends on the lense you use.
>> May  we have some details on the technics involved in this projection?
>>
>> Marc
> 
> Dear Marc
> 
> I don't have any special technic and i just wanna find a way to have
> a undistorted scene on a cylindrical screen with a ordinary projector.
> of course I prefer to do that by software modification not by hardware

	That's probably not possible. Sure you can find a software
transformation that will compensate the *distortion* (in fact, the
standard POV perspective camera should do it more or less), but your
main problem will be the *focus*. Ordinary projector have lenses
that only produce a sharp image on (or near) a certain plane. The
position of this plane may be adjusted, but it is always a plane.
This means that if your screen is a cylinder, you will have parts of
the screen which are in front of the focus plane and/or other parts
which are behind, and those parts will be out of focus and display a
blurred image.

		Jerome
- --
+------------------------- Jerome M. BERGER ---------------------+
|    mailto:jeb### [at] freefr      | ICQ:    238062172            |
|    http://jeberger.free.fr/     | Jabber: jeb### [at] jabberfr   |
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