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Fab wrote:
> Hello !
>
> I have a problem with perspective camera.
>
>
> - I use the following code for an image of 400x400 pixels.
> - I wish to get a cylinder in the middle of my image just like the image I
> sent.
Please don't post attachments in this group.
Apart from that you did not make it clear what you are trying to
achieve. If you want the cylinder to fill your whole image the radius
has to be the same as the distance to the camera if the camera angle is
90 degree. If your radius is 250 and the distance from the camera 500
(it's only 499 in your sample) the cylinder fills half the width of the
image.
Christoph
--
POV-Ray tutorials, include files, Sim-POV,
HCR-Edit and more: http://www.tu-bs.de/~y0013390/
Last updated 25 Oct. 2003 _____./\/^>_*_<^\/\.______
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> If you want the cylinder to fill your whole image the radius
> has to be the same as the distance to the camera if the camera angle is
> 90 degree. If your radius is 250 and the distance from the camera 500
> (it's only 499 in your sample) the cylinder fills half the width of the
> image.
ok. but it is exactly what I do not understand.
in optic, if the radius is 250, the cylinder should NOT fills half the width
of the image.
if I wished to fill half of the image, I need a radius of tan ( 90 / 4 ) *
499
and that's not the case with povray.
And my question is : Why isn'it like in optic with povray ?
( I need to use povray to build an scientific application but the
perspective camera does not work like it should.... or I do not understand
how it works.. )
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In article <3fa3bac8$1@news.povray.org>,
"Fab" <--fab### [at] u-picardie fr--> wrote:
> in optic, if the radius is 250, the cylinder should NOT fills half the width
> of the image.
>
> if I wished to fill half of the image, I need a radius of tan ( 90 / 4 ) *
> 499
> and that's not the case with povray.
I think you're misunderstanding the projection or the math. What you are
doing is projecting a 2D plane (that of the end of the cylinder) onto
another 2D plane (the image plane) through a pinhole camera. If you
double the radius of the cylinder, the apparent radius of the cylinder
will double. The radius you need to fill the image is tan(90/2)*499,
which happens to be 499. To fill half the image, you need
tan(90/2)*499/2.
--
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/
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Fab wrote:
>>If you want the cylinder to fill your whole image the radius
>>has to be the same as the distance to the camera if the camera angle is
>>90 degree. If your radius is 250 and the distance from the camera 500
>>(it's only 499 in your sample) the cylinder fills half the width of the
>>image.
>
>
> ok. but it is exactly what I do not understand.
>
> in optic, if the radius is 250, the cylinder should NOT fills half the width
> of the image.
>
> if I wished to fill half of the image, I need a radius of tan ( 90 / 4 ) *
> 499
> and that's not the case with povray.
>
> And my question is : Why isn'it like in optic with povray ?
POV-Ray is completely correct here. Just draw it on a piece of paper
and you will see.
Christoph
--
POV-Ray tutorials, include files, Sim-POV,
HCR-Edit and more: http://www.tu-bs.de/~y0013390/
Last updated 25 Oct. 2003 _____./\/^>_*_<^\/\.______
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