the radius of the long side of the ellips equals the radius of you cylinder
divided by the cosine of the angle of rotation.
the radius short side of the ellips doesn't change.
so if i'm not mistaken you can make a cylinder of limited height and then
scale it in the right direction by an amount of 1/cos(15*pi/180) where the
latter part converts your 15 degrees to radians.

"Rob Brown-Bayliss" <rob### [at] zoismorg> wrote in message
news:3d5f3f82@news.povray.org...
> Hi,
>
> I am having trouble with mathss, now I know this isn't a maths group, so
> ill explain my problem and pray for forgivness..
>
> I have a cylinder object, its verticle like a tower, then rotated (tilted
> like the tower of pisa) 15 degrees.
>
> I want to place a series of windows around the tower, but so that they
> appear paralel to the ground plane.  These windows are cutouts.
>
> The easy part is making each window vertical, by simply rotating it as I
> place them.  But the hard part (for me) is working out the shape or size
> of the elipse that a level floor would be...
>
> Am I being clear?  Even though it's a cylinder, because it's tilted the
> floor isnotacircle, so I need torotate the windows around an elipse...
>
> I can easily cut holes, but I want to place features on the cylinder
> surface.
>
> Were do I begin?
>
> Thanks

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