Dear Florian:

Thank you for your help.
My first attempt was to stack small parallelepipeds rotated by small angles.
Your solution gives a much better rendering.

I am new to pov-ray; so I still have a question: is your object solid? That is,
can it be subject to the difference operator?

Regards
Paulo Mota

> "Paulo Mota" <pmo### [at] gmailcom> wrote:
> > Can some one help me on the povray code to make the following solid:
> > A rectangle defined on the xz plane (with two opposite corners <-h,0,-m> and
> > <h,0,m>)
> > is sweeped (by a thickness e) and rotated (by an angle a) along the y axis.
> >
> > Regards,
> > Paulo Mota
>
> You could use an isosurface to get what you are looking for...
>
> I wrote a little scene code that does exactly that:
>
> camera {
>     location <0.75, 0.5, -1>*7
>     up y
>     right 4/3*x
>     look_at 0
>     angle 27
> }
>
> light_source {<1, 2.5, -2>*10  color rgb 1}
>
> #declare x_h = 0.75; // half of width
> #declare y_e = 1.25; // height
> #declare z_m = 0.25; // half of length
> #declare r_a = 135;  // rotation angle (degrees)
>
> #declare func_box = function {max (abs (x) - x_h, abs (y - y_e/2) - y_e/2, abs
> (z) - z_m)}
>
> #declare r_a_rad_y = radians (r_a)/y_e;
> #declare func_twist = function {func_box (x*cos (y*r_a_rad_y) - z*sin
> (y*r_a_rad_y), y, x*sin (y*r_a_rad_y) + z*cos (y*r_a_rad_y))}
>
> #declare twisted_box_iso =
> isosurface {
>     function {func_twist (x, y, z)}
>     contained_by {box {-2, 2}}
>     max_gradient 3
> }
>
> object {
>     twisted_box_iso
>     pigment {
>         wrinkles
>         color_map {
>             [0  color rgb y]
>             [1  color rgb z]
>         }
>     }
>     finish {phong 0.5}
> }
>
> plane {
>     y, 0
>     pigment {checker  color rgb <0.8, 0.2, 0.1>  color rgb <1, 0.3, 0.1>}
>     finish {diffuse 0.25  reflection {0.3}}
> }
>
> Regards,
> Florian

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