"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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