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.

Post a reply to this message

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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-----BEGIN PGP SIGNED MESSAGE-----
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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=s3SH
-----END PGP SIGNATURE-----

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"Hamed Ahmadi" <h.a### [at] hotmailcom> wrote in message 
news:web.472ad84c5849c6ccf104cee20@news.povray.org...
>> 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.
>

Hi Hamed,

Just to be sure we're on the same page...
You want to project onto a screen that forms an arc around the projector. 
The projector will be level and at the same height as the centre of the 
image on the screen. Your projector is a fairly ordinary projector, so will 
only send out an image straight ahead, and about 20 degrees left and right, 
up and down, so would only put an image on about 12% of a completely 
cylindrical screen?

If that's the case then you should be able to use the POV-Ray camera 
settings Marc suggested with a little trial and error. You may have 
difficulty getting the whole image in focus at the same time. I would 
imagine that projectors 'correct' the focus to get a good image on a flat 
screen. You'll need to adjust the up and right vectors to match the 
projector lens, but you should be able to use the test scene that Marc 
posted to 'calibrate' that.

If you don't want the projector to be level and at the centre point of the 
cylinder then it becomes a bit more difficult and I think you would probably 
need to render in two passes to deal with that properly. For example, if you 
want to project down from a ceiling mounted projector or if you want to 
project onto the outside of a cylindrical screen. In these cases the problem 
of getting the whole image in focus is also likely to be accentuated.

Regards,
Chris B.

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

Greetings from Perth, if I understand you correctly you want to create graphics
for a cylindrical display. I have done this for full 360 degree displays
including those that are additionally stereo. What you generally need to do is
twofold
1. Create your content as cylindrical panoramic images, I suggest just panoramic
of the right vertical field of view to match your projection environment. See
more details on the equations see
   http://local.wasp.uwa.edu.au/~pbourke/projection/stereopanoramic/procedure/

2. You then need to geometry correct (warp) the images so that when projected
using a (perspective) projector you get the right image on the cylinder. See
   http://local.wasp.uwa.edu.au/~pbourke/projection/cylinder/
and
   http://local.wasp.uwa.edu.au/~pbourke/projection/cylmapper/

-------------------------------------
P a u l   B o u r k e
http://local.wasp.uwa.edu.au/~pbourke/

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>  I had visited the pages and I was interested in them. They seems applicable
specially
>  "Image warping for projection onto a cylinder" part,
>  but I didn't find any algorithm or detailed information on it. Actually I'm
> just working on image warping.
>  Would you give me some detailed algorithms to implement it?

Well, there are lots of possible ways .... since you posted this to the PovRay
group, one way is to render a panoramic image of your scene using PovRay. Then
create a second model that consists of just a cylinder, the same dimensions as
the cylinder you plan to project onto and with your panoramic image applied as
a texture. Create a camera at the same location and of the same specifications
as your data projector. If you render this second scene then you will have the
correctly warped result. Note that since PovRay doesn't readily do offset
frustums then you need to get up to tricks like this to get the offset frustrum
your data projector creates.
   http://local.wasp.uwa.edu.au/~pbourke/projection/mirrorrender/

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